DNA MOLECULES ENCODING CTENOCEPHALIDES FELIS GLUTAMATE GATED CHLORIDE CHANNELS

Abstract: To date, L-glutamate-gated chloride (GluC1) channels have been observed only in invertebrate organisms. Modulators of this channel (either agonists or antagonists) will interfere with neurotransmission. For example, agents such as avermectins activate the GluCl, causing paralysis due to blocking of neurotransmitter release, resulting in death of the organism. Because GluCl channels are invertebrate specific, they are excellent targets for the discovery of novel insecticides, anthelminths and parasiticides that will display a marked safety profile because of the lack of mechanism based toxicity in vertebrate organisms. The present specification discloses isolation of a cDNA clone from the cat flea Ctenocephalides felis (CfGluCl-1) that encodes a L-glutamate-gated chloride channel. Heterologous expression of CfGluCl-1 cRNA in Xenopus oocytes results in robust expression of a L-glutamate-gated chloride current and the channel is activated and potentiated by avermectins. The expression of CfGluCl-1 in a heterologous expression system is useful to screens for novel GluCl channel agonists and antagonists. Additionally, this specification discloses improved methods of screening for GluCl channel modulators.

Description: TITLE OF THE INVENTION DNA MOLECULES ENCODING CTENOCEPHALIDES FELIS GLUTAMATE GATED CHLORIDE CHANNELS CROSS-REFERENCE TO RELATED APPLICATIONS This is a continuation of provisional application number 60/055,451 filed August 11, 1997. STATEMENT REGARDING FEDERALLY-SPONSORED R&D Not applicable. REFERENCE TO MICROFICHE APPENDLX Not applicable. FIELD OF THE INVENTION The present invention relates in part to isolated nucleic acid molecules (polynucleotides) which encode Ctenocephalides felis (flea) glutamate gated chloride channels. The present invention also relates to recombinant vectors and recombinant hosts which contain a DNA fragment encoding C. felis glutamate gated chloride channels, substantially purified forms of associated C. felis glutamate gated chloride channels, associated mutant proteins, and methods associated with identifying compounds which modulate associated Ctenocephalides felis glutamate gated chloride channels, which will be useful as insecticides. BACKGROUND OF THE INVENTION Glutamate-gated chloride channels, or H-receptors, have been identified in arthropod nerve and muscle (Lingle et al, 1981, Brain Res. 212: 481-488; Horseman et al., 1988, Neurosci. Lett. 85: 65-70; Wafford and Sattelle, 1989, J. Exp. Bio. 144: 449-462; Lea and Usherwood, 1973, Comp. Gen. Parmacol. 4: 333-350; and Cull-Candy, 1976, J. Physiol. 255: 449-464). Additionally, glutamate-gated chloride channels have been cloned from the soil nematode Caenorhabditis elegans (Cully et al., 1994, Nature 371: 707-711; see also U.S. Patent No. 5,527,703) and Drosophila melanogaster (Cully et al., 1996, J. Biol. Chem. 271: 20187- 20191). Invertebrate glutamate-gated chloride channels are important targets for the widely used avermectin class of anthelmintic and insecticidal compounds. The avermectins are a family of macrocyclic lactones originally isolated from the actinomycete Streptomyces avermitilis. The semisynthetic avermectin derivative, ivermectin (22,23-dihydro-avermectin Bχ a ), is used throughout the world to treat parasitic helminths and insect pests of man and animals. The avermectins remain the most potent broad spectrum endectocides exhibiting low toxicity to the host. After many years of use in the field, there remains little resistance to avermectin in the insect population. The combination of good therapeutic index and low resistance strongly suggests that the glutamate-gated chloride (GluCl) channels remain good targets for insecticide development. It would be advantageous to identify additional invertebrate genes encoding encoding GluCl channels in order to allow screening to identify novel GluCl channel modulators that may have insecticidal, mitacidal and/or nematocidal activity for animal health or crop protection. The present invention addresses and meets these needs by disclosing isolated nucleic acid molecules which express a Ctenocephalides felis GluGl channel wherein expression of flea GluCl cRNA in Xenopus oocytes results in an active GluCl channel. SUMMARY OF THE INVENTION The present invention relates to isolated nucleic acid molecules (polynucleotides) which encode novel invertebrate GluCl channel proteins, especially nucleic acid molecules which encode a functional C. felis GluCl (herein, "CfGluCl") channel. The present invention also relates to isolated nucleic acid fragments of CfGluCl which encode mRNA expressing a biologically active CfGluCl channel. Any such polynucleotide includes but is not necessarily limited to nucleotide substitutions, deletions, additions, amino-terminal truncations and carboxy-terminal truncations such that these mutations encode cRNA which express a functional C. felis GluCl channel in a eukaryotic cell, such as Xenopus oocytes, so as to be useful for screening for agonists and/or antagonists of C. felis GluCl activity. The isolated nucleic acid molecule of the present invention may include a deoxyribonucleic acid molecule (DNA), such as genomic DNA and complementary DNA (cDNA), which may be single (coding or noncoding strand) or double stranded, as well as synthetic DNA, such as a synthesized, single stranded polynucleotide. The isolated nucleic acid molecule of the present invention may also include a ribonucleic acid molecule (RNA), including but not limited to messenger RNA (mRNA) encoding a biologically active C. felis GluCl channel and complementary RNA (cRNA) transcribed from a recombinant expression vector comprising a DNA molecule which encodes a full-length or biologically active portion of the full-length C. felis GluCl channel. A preferred aspect of the present invention is disclosed in Figures 1A-B and SEQ ID NO:l, an isolated cDNA molecule encoding a C. felis GluCl channel, CfGluCl-1. The present invention relates to recombinant vectors and recombinant hosts, both prokaryotic and eukaryotic, which contain the substantially purified nucleic acid molecules disclosed throughout this specification, especially a nucleic acid molecule encoding a C. felis GluCl channel, CfGluCl, such as the cDNA molecule disclosed in Figures 1A-B and set forth in SEQ ID NO:l. The present invention also relates to a substantially purified form of a C. felis GluCl channel protein and especially the C. felis GluCl channel disclosed in Figure 2 and set forth in SEQ ID NO:2. The present invention relates to a substantially purified membrane preparation which comprises a C. felis GluCl channel and is essentially free from contaminating proteins, including but not limited to other C. felis source proteins or host proteins from a recombinant cell which expresses CfGluCl. Especially preferred is a membrane preparation which comprises C. felis GluCl channel disclosed in Figure 2 and set forth in SEQ ID NO:2. To this end, the present invention also relates to a substantially purified membrane preparation which is purified from a recombinant host, whether a recombinant eukaryotic or recombinant prokaryotic host, wherein a recombinant vector expresses a C. felis GluCl channel. Especially preferred is a membrane preparation which comprises a recombinant form of the C. felis GluCl channel, CfGluCl, disclosed in Figure 2 and set forth in SEQ ID NO:2, referred to as CfGluCl-1. The present invention also relates to biologically active fragments and/or mutants of a C. felis GluCl channel protein, including but not limited to the CfGluCl protein disclosed in Figure 2 and set forth in SEQ ID NO:2, including but not necessarily limited to amino acid substitutions, deletions, additions, amino terminal truncations and carboxy-terminal truncations such that these mutations provide for a biologically active channel which is useful in screening for agonists and/or antagonists of C. felis GluCl channel activity. The present invention also relates to an isolated nucleic acid molecule (polynucleotide) which encodes a truncated form of the flea GluCl channel protein (herein, "tr-CfGluCl"), as exemplified in Figure 3 and set forth in SEQ ID NO:3. Co-expression of tr-CfGluCl in Xenopus oocytes with CfGluCl is shown to inhibit glutamate-gated channel activity. The present invention also relates to isolated nucleic acid fragments of tr-CfGluCl-1 (SEQ ID NO:3) which encodes cRNA expressing a biologically active form of tr-CfGluCl, including but not limited to inhibition or promotion of CfGluCl channel activity in the target cell type. Any such polynucleotide includes but is not necessarily limited to nucleotide substitutions, deletions, additions, amino-terminal truncations and carboxy-terminal truncations from the truncated form. Again, any such truncated nucleic acid molecule (as compared to CfGluCl) may include a deoxyribonucleic acid molecule (DNA), such as genomic DNA and complementary DNA (cDNA), which may be single (coding or noncoding strand) or double stranded, as well as synthetic DNA, such as a synthesized, single stranded polynucleotide. The isolated nucleic acid molecule of the present invention may also include a ribonucleic acid molecule (RNA), including but not limited to messenger RNA (mRNA) or complementary RNA (cRNA) transcribed from a recombinant expression vector comprising a DNA molecule which encodes a truncated version of the full-length C. felis GluCl channel. A preferred aspect of this portion of the invention is disclosed in Figures 3A-B and SEQ ID NO:4, an isolated cDNA molecule encoding a truncated version of the C. felis GluCl channel. The present invention also relates to recombinant vectors and recombinant hosts, both prokaryotic and eukaryotic, which contain the substantially purified nucleic acid molecules disclosed throughout this specification, especially a nucleic acid molecule encoding a truncated version of a C. felis GluCl channel such as the cDNA molecule disclosed in Figures 3A-B and set forth in SEQ ID NO:3. The present invention also relates to a substantially purified form of a truncated version of the C. felis GluCl channel, trCfGluCl, and especially the truncated version of the C. felis GluCl channel, which is disclosed in Figure 4 and as set forth in SEQ ID NO:4, referred to as trCfGluCl- 1. The present invention also relates to biologically active fragments and/or mutants of the truncated C. felis GluCl channel, trCfGluCl- 1, including but not necessarily limited to amino acid substitutions, deletions, additions, amino terminal truncations and carboxy-terminal truncations. It is an object of the present invention to provide an isolated nucleic acid molecule which encodes a novel form of a C. felis GluCl channel and biologically active fragments thereof which are derivatives of SEQ ID NO:2. It is a further object of the present invention to provide the C. felis GluCl channel proteins or protein fragments encoded by the nucleic acid molecules referred to in the preceding paragraph. It is a further object of the present invention to provide recombinant vectors and recombinant host cells which comprise a nucleic acid sequence encoding a C. felis GluCl channel or a biological equivalent thereof. It is an object of the present invention to provide a substantially purified form of a C. felis GluCl channel or a biological equivalent thereof, as set forth in SEQ ID NO:2. It is also an object of the present invention to provide a membrane preparation membrane preparation which comprises a C. felis GluCl channel and is essentially free from contaminating proteins. This membrane preparation includes, but is not limited to, a membrane preparation purified from a recombinant host. It is an object of the present invention to provide for biologically active fragments and/or mutants of CfGluCl, including but not necessarily limited to amino acid substitutions, deletions, additions, amino terminal truncations and carboxy-terminal truncations such that these mutations provide for proteins or protein fragments of diagnostic, therapeutic or prophylactic use. It is an object of the present invention to provide a substantially purified form of CfGluCl-l, as set forth in SEQ ID NO:4. It is an object of the present invention to provide for biologically active fragments and/or mutants of CfGluCl, including but not necessarily limited to amino acid substitutions, deletions, additions, amino terminal truncations and carboxy-terminal truncations. As used herein, "GluCl" refers to a glutamate-gated chloride channel. As used herein, "CfGluCl" refers to a biologically active form of a C. felis glutamate-gated chloride channel. As used herein, "cDNA" refers to complementary DNA. As used herein, "mRNA" refers to messenger RNA. As used herein, "cRNA" refers to complementary RNA, transcribed from a recombinant cDNA template. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1A-B shows the nucleotide sequence which comprises the open reading frame encoding the C. felis GluCl channel, CfGluCl- 1. Figure 2 shows the amino acid sequence of CfGluCl- 1. Figures 3A-B shows the nucleotide sequence which comprises the open reading frame encoding the truncated C. felis GluCl channel, trCfGluCl-1. Figure 4 shows the amino acid sequence of trCfGluCl- 1. Figures 5 A and 5B show activation of CfGluCl- 1 by glutamate. Figure 5A shows superimposed current recordings in response to 10, 30, 100 and 300 μM glutamate. Figure 5B shows the concentration-response curve for glutamate. Figure 6 shows that the CfGluCl- 1 channel is selective for chloride. Figures 7A and 7B show that ivermectin phosphate (IVM- PO 4 ) is an agonist of the C felis GluCl channel encoded by CfGluCl-1. Figure 7A shows superimposed current recordings showing activation by 100 μM glutamate and 10 nM IVM-PO 4 . Figure 7B shows the concentration-response curve for IVM-PO 4 for CfGluCl (0 mV), DmGluCl (0 mV) and DmGluCl (-80 mV). DETAILED DESCRIPTION OF THE INVENTION L-glutamate-gated chloride (GluCl) channels have been observed only in invertebrate organisms. A modulator of this channel (either an agonist or antagonist) will interfere with neurotransmission. Agents such as avermectins activate this channel and cause paralysis due to block of neurotranmitter release, resulting in death of the organism. Because GluCl channels are invertebrate specific, they are excellent targets for the discovery of novel insecticides, anthelminthics and parasiticides that will display a marked safety profile because of the lack of mechanism based toxicity in vertebrate organisms. The present invention relates to isolated nucleic acid molecules (polynucleotides) which encode novel invertebrate GluCl channel proteins, especially nucleic acid molecules which encode a functional C. felis GluCl channel (herein, "CfGluCl"). Heterologous expression of CfGluCl cRNA in Xenopus oocytes results in robust expression of a L-glutamate-gated chloride current. The CfGluCl channel is activated and potentiated by avermectins (e.g., ivermectin phosphate). The expression of CfGluCl- 1 in a heterologous expression system can be used to establish screens for novel GluCl channel modulators. Such compounds will be useful as antiparasitics and insecticides in human and animal health and crop protection, because they will be devoid of mechanism based vertebrate toxicity. To this end, the present invention also relates to isolated nucleic acid fragments of CfGluCl which encode cRNA expressing a biologically CfGluCl channel. Any such polynucleotide includes but is not necessarily limited to nucleotide substitutions, deletions, additions, amino-terminal truncations and carboxy-terminal truncations such that these mutations encode cRNA which express a functional C. felis GluCl channel in a eukaryotic cell, such as Xenopus oocytes, so as to be useful for screening for agonists and or antagonists of C. felis GluCl activity. A preferred aspect of the present invention is disclosed in Figures 1A-B and SEQ ID NO:l, an isolated cDNA molecule encoding a C. felis GluCl channel, CfGluCl- The present invention also relates to recombinant vectors and recombinant hosts, both prokaryotic and eukaryotic, which contain the substantially purified nucleic acid molecules disclosed throughout this specification, especially a nucleic acid molecule encoding a C. felis GluCl channel, CfGluCl, such as the cDNA molecule disclosed in Figures 1A-B and set forth in SEQ ID NO:l. The isolated nucleic acid molecule of the present invention may include a deoxyribonucleic acid molecule (DNA), such as genomic DNA and complementary DNA (cDNA), which may be single (coding or noncoding strand) or double stranded, as well as synthetic DNA, such as a synthesized, single stranded polynucleotide. The isolated nucleic acid molecule of the present invention may also include a ribonucleic acid molecule (RNA), including but not limited to messenger RNA (mRNA) encoding a biologically active C. felis GluCl channel and complementary RNA (cRNA) transcribed from a recombinant expression vector comprising a DNA molecule which encodes a full-length or biologically active portions of the full-length C. felis GluCl channel. It is known that there is a substantial amount of redundancy in the various codons which code for specific amino acids. Therefore, this invention is also directed to those DNA sequences transcribing mRNA or cRNA comprising alternative codons which encode an identical amino acid, as shown below: A=Ala=Alanine: codons GCA, GCC, GCG, GCU C=Cys=Cysteine: codons UGC, UGU D=Asp=Aspartic acid: codons GAC, GAU E=Glu=Glutamic acid: codons GAA, GAG F=Phe=Phenylalanine: codons UUC, UUU G=Gly=Glycine: codons GGA, GGC, GGG, GGU H=His=Histidine: codons CAC, CAU I=Ile=Isoleucine: codons AUA, AUC, AUU K=Lys=Lysine: codons AAA, AAG L=Leu=Leucine: codons UUA, UUG, CUA, CUC, CUG, CUU M=Met=Methionine: codon AUG N=Asp=Asparagine: codons AAC, AAU P=Pro=Proline: codons CCA, CCC, CCG, CCU Q=Gln=Glutamine: codons CAA, CAG R=Arg= Arginine: codons AGA, AGG, CGA, CGC, CGG, CGU S=Ser=Serine: codons AGC, AGU, UCA, UCC, UCG, UCU T=Thr=Threonine: codons ACA, ACC, ACG, ACU V=Val=Valine: codons GUA, GUC, GUG, GUU W=Trp=Tryptophan: codon UGG Y=Tyr=Tyrosine: codons UAC, UAU Therefore, the present invention discloses codon redundancy which may result in differing DNA molecules expressing an identical protein. For purposes of this specification, a sequence bearing one or more replaced codons will be defined as a degenerate variation. Also included within the scope of this invention are mutations either in the DNA sequence or the translated protein which do not substantially alter the ultimate physical properties of the expressed protein. For example, substitution of valine for leucine, arginine for lysine, or asparagine for glutamine may not cause a change in functionality of the polypeptide. It is known that DNA sequences coding for a peptide may be altered so as to code for a peptide having properties that are different than those of the naturally occurring peptide. Methods of altering the DNA sequences include but are not limited to site-directed mutagenesis. Examples of altered properties include but are not limited to changes in the affinity of an enzyme for a substrate or a receptor for a ligand. As used herein, "purified" and "isolated" are utilized interchangeably to stand for the proposition that the nucleic acid, protein, or respective fragment thereof in question has been substantially removed from its in vivo environment so that it may be manipulated by the skilled artisan, such as but not limited to nucleotide sequencing, restriction digestion, site-directed mutagenesis, and subcloning into expression vectors for a nucleic acid fragment as well as obtaining the protein or protein fragment in pure quantities so as to afford the opportunity to generate polyclonal antibodies, monoclonal antibodies, amino acid sequencing, and peptide digestion. Therefore, the nucleic acids claimed herein may be present in whole cells or in cell lysates or in a partially purified or substantially purified form. A nucleic acid is considered substantially purified when it is purified away from environmental contaminants. Thus, a nucleic acid sequence isolated from cells is considered to be substantially purified when purified from cellular components by standard methods while a chemically synthesized nucleic acid sequence is considered to be substantially purified when purified from its chemical precursors. The present invention also relates to a substantially purified form of a C. felis GluCl channel, CfGluCl, and especially the C. felis GluCl channel which is disclosed in Figure 2 and as set forth in SEQ ID NO:2, referred to as CfGluCl-1. The present invention also relates to a substantially purified membrane preparation which comprises a C. felis GluCl channel and is essentially free from contaminating proteins. Especially preferred is a membrane preparation which comprises a C. felis GluCl channel disclosed in Figure 2 and set forth in SEQ ID NO:2, referred to as CfGluCl- 1. The present invention also relates to a substantially purified membrane preparation which is purified from a recombinant host, whether a recombinant eukaryotic or recombinant prokaryotic host, wherein a recombinant vector expresses a C. felis GluCl channel. Especially preferred is a membrane preparation which comprises a recombinant form of the C. felis GluCl channel, CfGluCl, disclosed in Figure 2 and set forth in SEQ ID NO:2, referred to as CfGluCl-1. The present invention also relates to biologically active fragments and/or mutants of CfGluCl- 1, including but not necessarily limited to amino acid substitutions, deletions, additions, amino terminal truncations and carboxy-terminal truncations such that these mutations provide for a biologically active channel which is useful in screening for agonists and/or antagonists of C. felis GluCl channel activity. As used herein, a "biologically active equivalent" or "functional derivative" of a wild-type C. felis GluCl channel possesses a biological activity that is substantially similar to the biological activity of the wild type C. felis GluCl channel. The term "functional derivative" is intended to include the "fragments," "mutants," "variants," "degenerate variants," "analogs" and "homologues" or to "chemical derivatives" of the wild type C. felis GluCl channel protein. The term "fragment" is meant to refer to any polypeptide subset of a wild-type C. felis GluCl channel. The term "mutant" is meant to refer to a molecule that may be substantially similar to the wild-type form but possesses distinguishing biological characteristics. Such altered characteristics include but are in no way limited to altered substrate binding, altered substrate affinity and altered sensitivity to chemical compounds affecting biological activity of the C. felis GluCl channel and/or C. felis GluCl channel derivative. The term "variant" is meant to refer to a molecule substantially similar in structure and function to either the entire wild- type protein or to a fragment thereof. A molecule is "substantially similar" to a wild-type C. felis GluCl channel and/or C. felis GluCl channel-like protein if both molecules have substantially similar structures or if both molecules possess similar biological activity. Therefore, if the two molecules possess substantially similar activity, they are considered to be variants even if the structure of one of the molecules is not found in the other or even if the two amino acid sequences are not identical. The term "analog" refers to a molecule substantially similar in function to either the full-length C. felis GluCl channel and/or C. felis GluCl channel or to a biologically active fragment thereof. The present invention also relates to isolated an isolated nucleic acid molecule (polynucleotide) which encodes a truncated form of the flea GluCl channel protein (herein, "tr-CfGluCl"), as exemplified in Figures 3A-B and SEQ ID NO:3. Co-expression of tr-CfGluCl in Xenopus oocytes with CfGluCl inhibits glutamate-gated channel activity. The present invention also relates to isolated nucleic acid fragments of SEQ ID NO:3 which encode cRNA expressing a biologically active form of tr-CfGluCl, including but not limited to inhibition or promotion of CfGluCl channel activity in the target cell type. Any such polynucleotide includes but is not necessarily limited to nucleotide substitutions, deletions, additions, amino-terminal truncations and carboxy-terminal truncations from the truncated form. Again, any such truncated nucleic acid molecule (as compared to CfGluCl) may include a deoxyribonucleic acid molecule (DNA), such as genomic DNA and complementary DNA (cDNA), which may be single (coding or noncoding strand) or double stranded, as well as synthetic DNA, such as a synthesized, single stranded polynucleotide. The isolated nucleic acid molecule of the present invention may also include a ribonucleic acid molecule (RNA), including but not limited to messenger RNA (mRNA) or complementary RNA (cRNA) transcribed from a recombinant expression vector comprising a DNA molecule which encodes a truncated version of the full-length C. felis GluCl channel. The present invention also relates to recombinant vectors and recombinant hosts, both prokaryotic and eukaryotic, which contain the substantially purified nucleic acid molecules disclosed throughout this specification, especially a nucleic acid molecule encoding a truncated version of a C. felis GluCl channel, CfGluCl., such as the cDNA molecule disclosed in Figures 3A-B and set forth in SEQ ID NO:3. The present invention also relates to a substantially purified form of a truncated version of the C. felis GluCl channel, trCfGluCl, and especially the truncated version of theC. felis GluCl channel, which is disclosed in Figure 4 and as set forth in SEQ ID NO:4, referred to as trCfGluCl-1. The present invention also relates to biologically active fragments and/or mutants of trCfGluCl- 1, including but not necessarily limited to amino acid substitutions, deletions, additions, amino terminal truncations and carboxy-terminal truncations. Any of a variety of procedures may be used to clone a C. felis GluCl channel. These methods include, but are not limited to, (1) a RACE PCR cloning technique (Frohman, et al., 1988, Proc. Natl. Acad. Sci. USA 85: 8998-9002). 5' and/or 3' RACE may be performed to generate a full-length cDNA sequence. This strategy involves using gene-specific oligonucleotide primers for PCR amplification of C. felis GluCl channel cDNA. These gene-specific primers are designed through identification of an expressed sequence tag (EST) nucleotide sequence which has been identified by searching any number of publicly available nucleic acid and protein databases; (2) direct functional expression of the C. felis GluCl channel cDNA following the construction of a C. felis GluCl channel- containing cDNA library in an appropriate expression vector system; (3) screening a C. felis GluCl channel- containing cDNA library constructed in a bacteriophage or plasmid shuttle vector with a labeled degenerate oligonucleotide probe designed from the amino acid sequence of the C. felis GluCl channel protein; and (4) screening a C. felis GluCl channel- containing cDNA library constructed in a bacteriophage or plasmid shuttle vector with a partial cDNA encoding the C. felis GluCl channel protein. This partial cDNA is obtained by the specific PCR amplification of C. felis GluCl channel DNA fragments through the design of degenerate oligonucleotide primers from the amino acid sequence known for other kinases which are related to the C. felis GluCl channel protein; (5) screening a C. felis GluCl channel-containing cDNA library constructed in a bacteriophage or plasmid shuttle vector with a partial cDNA encoding the C. felis GluCl channel protein. This strategy may also involve using gene-specific oligonucleotide primers for PCR amplification of C. felis GluCl channel cDNA identified as an EST as described above; or (6) designing 5' and 3' gene specific oligonucleotides using SEQ ID NO: 1 as a template so that either the full-length cDNA may be generated by known RACE techniques, or a portion of the coding region may be generated by these same known RACE techniques to generate and isolate a portion of the coding region to use as a probe to screen one of numerous types of cDNA and/or genomic libraries in order to isolate a full-length version of the nucleotide sequence encoding C. felis GluCl channel. It is readily apparent to those skilled in the art that suitable cDNA libraries may be prepared from cells or cell lines which have C. felis GluCl channel activity. The selection of cells or cell lines for use in preparing a cDNA library to isolate a cDNA encoding C. felis GluCl channel may be done by first measuring cell-associated C. felis GluCl channel activity using any known assay available for such a purpose. Preparation of cDNA libraries can be performed by standard techniques well known in the art. Well known cDNA library construction techniques can be found for example, in Sambrook et al., 1989, Molecular Cloning: A Laboratory Manual; Cold Spring Harbor Laboratory, Cold Spring Harbor, New York. Complementary DNA libraries may also be obtained from numerous commercial sources, including but not limited to Clontech Laboratories, Inc. and Stratagene. It is also readily apparent to those skilled in the art that DNA encoding C. felis GluCl channel may also be isolated from a suitable genomic DNA library. Construction of genomic DNA libraries can be performed by standard techniques well known in the art. Well known genomic DNA library construction techniques can be found in Sambrook, et al., supra. In order to clone the C. felis GluCl channel gene by one of the preferred methods, the amino add sequence or DNA sequence of C. felis GluCl channel or a homologous protein may be necessary. To accomplish this, the C. felis GluCl channel protein or a homologous protein may be purified and partial amino add sequence determined by automated sequenators. It is not necessary to determine the entire amino acid sequence, but the linear sequence of two regions of 6 to 8 amino acids can be determined for the PCR amplification of a partial C. felis GluCl channel DNA fragment. Once suitable amino acid sequences have been identified, the DNA sequences capable of encoding them are synthesized. Because the genetic code is degenerate, more than one codon may be used to encode a particular amino acid, and therefore, the amino add sequence can be encoded by any of a set of similar DNA oligonucleotides. Only one member of the set will be identical to the C. felis GluCl channel sequence but others in the set will be capable of hybridizing to C. felis GluCl channel DNA even in the presence of DNA oligonucleotides with mismatches. The mismatched DNA oligonucleotides may still sufficiently hybridize to the C. felis GluCl channel DNA to permit identification and isolation of C. felis GluCl channel encoding DNA. Alternatively, the nucleotide sequence of a region of an expressed sequence may be identified by searching one or more available genomic databases. Gene-specific primers may be used to perform PCR amplification of a cDNA of interest from either a cDNA library or a population of cDNAs. As noted above, the appropriate nucleotide sequence for use in a PCR-based method may be obtained from SEQ ID NO: 1, either for the purpose of isolating overlapping 5' and 3' RACE products for generation of a full-length sequence coding for C. felis GluCl channel, or to isolate a portion of the nucleotide sequence coding for C. felis GluCl channel for use as a probe to screen one or more cDNA- or genomic-based libraries to isolate a full-length sequence encoding C. felis GluCl channel or C. felis GluCl channel-like proteins. In an exemplified method, a C. felis GluCl channel cDNA was generated by screening a C. felis cDNA library prepared in the phagemid cloning vector λZAPII (Stratagene, LaJolla, CA) This library was screened with a DNA probe corresponding to nucleotides 471 to 1760 of the DrosGluCl cDNA (Cully et al., 1996, J. Biol. Chem. 271: 20187- 20191; accession number U58776) which codes for all but the last four amino acids of the Drosophila glutamate-gated chloride channel. Two positive clones, F5A and F6 were chosen for further analysis. These cDNA clones were shown to encode a truncated polypeptide disclosed in Figure 4 and SEQ ID NO:4, referred to within this spedfication as trCfGluCl-1. It is shown in this specification that the truncation at the amino-terminal region of clone F5A produced a frame shift mutation. It is also shown in this spedfication that this truncation was in fact due to a deletion of 71 nucleotides at the presumptive amino-terminal extracellular domain, resulting in a frame shift mutation that resulted in expression of the truncated protein, trCfGluCl-1. A cDNA fragment containing the missing portion of a putative C. felis GluCl channel cDNA was generated by PCR amplification of randomly primed flea cDNA. Primer-1 (5'-CTCAGAGTCAGGATCCGGCTA-3'; SEQ ID NO:5) and Primer-2 (5'-CTGAAAGTTAACTGGACACTG-3'; SEQ ID NO:6) were used in a standard PCR reaction to amplify a 532 bp PCR fragment that was shown by DNA sequence analysis to contain the missing 71 nucleotides and flanking sequences disclosed in the F5A clone. A 517 bp BamHI/Hpal fragment of this PCR product was isolated and inserted into a BamHI/Hpal digested F5A clone to generate the full length cDNA clone designated Fleaδl, as shown in Figures 1A-B. This cDNA molecule contains an open reading frame which encodes a C. felis GluCl channel, as shown in Figure 2, as set forth as SEQ ID NO:2. In addition, the 5' untranslated region the exemplified cDNA which encodes a CfGluCl channel protein was determined and is presented as SEQ ID NO:7. A variety of mammalian expression vectors may be used to express a recombinant C. felis GluCl channel protein in mammalian cells. Expression vectors are defined herein as DNA sequences that are required for the transcription of cloned DNA and the translation of their mRNAs in an appropriate host. Such vectors can be used to express eukaryotic DNA in a variety of hosts such as bacteria, blue green algae, plant cells, insect cells and animal cells. Specifically designed vectors allow the shuttling of DNA between hosts such as bacteria-yeast or bacteria-animal cells. An appropriately constructed expression vector should contain: an origin of replication for autonomous replication in host cells, selectable markers, a limited number of useful restriction enzyme sites, a potential for high copy number, and active promoters. A promoter is defined as a DNA sequence that directs RNA polymerase to bind to DNA and initiate RNA synthesis. A strong promoter is one which causes mRNAs to be initiated at high frequency. Expression vectors may include, but are not limited to, cloning vectors, modified cloning vectors, specifically designed plasmids or viruses. Commercially available mammalian expression vectors which may be suitable for recombinant C. felis GluCl channel protein expression, include but are not limited to, pcDNA3.1 (Invitrogen), pLITMUS28, pLITMUS29, pLITMUS38 and pLITMUS39 (New England Bioloabs), pcDNAI, pcDNAIamp (Invitrogen), pcDNA3 (Invitrogen), pMClneo (Stratagene), pXTl (Stratagene), pSG5 (Stratagene), EBO- pSV2-neo (ATCC 37593) pBPV- 1(8-2) (ATCC 37110), pdBPV-MMTneo(342- 12) (ATCC 37224), pRSVgpt (ATCC 37199), pRSVneo (ATCC 37198), pSV2- dhfr (ATCC 37146), pUCTag (ATCC 37460), and λZD35 (ATCC 37565). A variety of bacterial expression vectors may be used to express a recombinant C. felis GluCl channel protein in bacterial cells. Commercially available bacterial expression vectors which may be suitable for recombinant C felis GluCl channel protein expression include, but are not limited to pCR2.1 (Invitrogen), pETlla (Novagen), lambda gtll (Invitrogen), and pKK223-3 (Pharmacia). A variety of fungal cell expression vectors may be used to express recombinant C. felis GluCl channel protein in fungal cells. Commerdally available fungal cell expression vectors which may be suitable for recombinant C. felis GluCl channel expression include but are not limited to pYES2 (Invitrogen) and Pichia expression vector (Invitrogen). A variety of insect cell expression vectors may be used to express recombinant receptor in insect cells. Commercially available insect cell expression vectors which may be suitable for recombinant expression of a C. felis GluCl channel protein include but are not limited to pBlueBacIII and pBlueBacHis2 (Invitrogen), and pAcG2T (Pharmingen). An expression vector containing DNA encoding a C. felis GluCl channel protein and/or C. felis GluCl channel-like protein may be used for expression of C. felis GluCl channel protein in a recombinant host cell. Recombinant host cells may be prokaryotic or eukaryotic, including but not limited to bacteria such as E. coli, fungal cells such as yeast, mammalian cells including but not limited to cell lines of human, bovine, pordne, monkey and rodent origin, and insect cells including but not limited to Drosophila- and silkworm-derived cell lines. Cell lines derived from mammalian species which may be suitable and which are commerdally available, include but are not limited to, L cells L-M(TK") (ATCC CCL 1.3), L cells L-M (ATCC CCL 1.2), Saos-2 (ATCC HTB-85), 293 (ATCC CRL 1573), Raji (ATCC CCL 86), CV-1 (ATCC CCL 70), COS-1 (ATCC CRL 1650), COS-7 (ATCC CRL 1651), CHO-K1 (ATCC CCL 61), 3T3 (ATCC CCL 92), NIH/3T3 (ATCC CRL 1658), HeLa (ATCC CCL 2), C127I (ATCC CRL 1616), BS-C-1 (ATCC CCL 26), MRC-5 (ATCC CCL 171) and CPAE (ATCC CCL 209). The cloned human C. felis GluCl channel cDNA obtained through the methods described above may be recombinantly expressed by molecular cloning into an expression vector (such as pcDNA3.1, pCR2.1, pBlueBacHis2 and pLITMUS28) containing a suitable promoter and other appropriate transcription regulatory elements, and transferred into prokaryotic or eukaryotic host cells to produce recombinant C. felis GluCl channel protein. Techniques for such manipulations can be found described in Sambrook, et al., supra, are discussed at length in the Example section and are well known and easily available to the artisan of ordinary skill in the art. The expression vector may be introduced into host cells via any one of a number of techniques including but not limited to direct injection, transformation, transfection, protoplast fusion, lipofection, and electroporation. The expression vector-containing cells are clonally propagated and individually analyzed to determine whether they produce C. felis GluCl protein. Identification of C. felis GluCl expressing host cell clones may be done by several means, including but not limited to immunological reactivity with anti-C. felis GluCl antibodies, and the presence of host cell-assodated GluCl activity. Expression of C. felis GluCl DNA may also be performed using in vitro produced synthetic mRNA. Synthetic mRNA can be efficiently translated in various cell-free systems, including but not limited to wheat germ extracts and reticulocyte extracts, as well as effidently translated in cell based systems, including but not limited to microinjection into frog oocytes, with microinjection into frog oocytes being preferred. To determine the C. felis GluCl channel cDNA sequence(s) that yields optimal levels of C. felis GluCl channel protein, cDNA molecules including but not limited to the following can be constructed: a cDNA fragment containing the full-length open reading frame for C. felis GluCl channel protein as well as various constructs containing portions of the cDNA encoding only spedfic domains of the protein or rearranged domains of the protein. All constructs can be designed to contain none, all or portions of the 5' and/or 3' untranslated region of a C. felis GluCl channel cDNA. The expression levels and activity of C. felis GluCl channel protein can be determined following the introduction, both singly and in combination, of these constructs into appropriate host cells. Following determination of the C. felis GluCl channel cDNA cassette yielding optimal expression in transient assays, this C. felis GluCl channel cDNA construct is transferred to a variety of expression vectors (including recombinant viruses), including but not limited to those for expression in host cells including, but not limited to, mammalian cells, insect cells such as baculovirus-infected insect cells, oocytes such as Xenopus oocytes, bacterial such asE. coli, and the yeast S. cerevisiae. The present invention also relates to methods of expressing an active C. felis GluCl channel protein and biological equivalents disclosed herein, assays employing these recombinantly expressed gene products, cells expressing these gene products, and agonistic and/or antagonistic compounds identified through the use of assays utilizing these recombinant forms, including, but not limited to, one or more modulators of a C. felis GluCl channel. A preferred expression system for the electrophysiological- based assays and related improved methods of measuring glutamate- gated chloride channel activity and modulation comprise injecting nucleic acid molecules into Xenopus laevis oocytes. The general use of Xenopus oocytes in the study of ion channel activity is known in the art (Dascal, 1987, Crit. Rev. Biochem. 22: 317-317; Lester, 1988, Science 241: 1057-1063; see also Methods ofEnzymology, Vol. 207, 1992, Ch. 14-25, Rudy and Iverson, ed., Academic Press, Inc., New York). A portion of the present invention discloses an improved method of measuring channel acitivity and modulation by agonists and/or antagonists which is several-fold more sensitive than previosly disclosed. The Xenopus oocytes are injected with nucleic acid material, including but not limited to DNA, mRNA or cRNA which encode a gated-channel, wherein channel activity may be measured as well as response of the channel to various modulators. To this end, the present invention relates to an improved in vitro method of measuring ion channel activity in eukaryotic cells, especially Xenopus oocytes, which comprises utilizing a holding potential more positive than the reversal potential for chloride (i.e, greater than -30 mV), preferably about 0 mV. This alteration in assay measurement conditions has resulting in a 10-fold increase in sensitivity of the assay to modulation by ivermectin phosphate. Therefore, this improved assay will allow screening and selecting for compounds which modulate GluCl activity at levels which were previously thought to be undetectable. Data is presented in Example Section 2 which exemplifies the use of this improved assay for detecting expressed ion channel activity in Xenopus oocytes. It will be evident to the skilled artisan that this improved method may be utilized in various ion channel measurement assays, and especially assays which measure glutamate-gated activity in a eukaryotic cell, such as a Xenopus oocyte. It is especially preferred that invertebrate glutamate-gated chloride channels, including but in not way limited to Caenorhabditis elegans, Drosophila melonogaster and Ctenocephalides felis glutamate-gated channel proteins, be utilized in an assay to screen and select for compounds which modulate the activity of these channels. Levels of C. felis GluCl protein in host cells are quantitated by immunoaffinity and/or ligand affinity techniques. Cells expressing GluCl can be assayed for the number of GluCl molecules expressed by measuring the amount of radioactive glutamate or ivermectin binding to cell membranes. GluCl-specific affinity beads or GluCl-specific antibodies are used to isolate for example ^S-methionine labelled or unlabelled GluCl protein. Labelled GluCl protein is analyzed by SDS- PAGE. Unlabelled GluCl protein is detected by Western blotting, ELISA or RIA assays employing GluCl specific antibodies. Recombinant C. felis GluCl channel protein can be separated from other cellular proteins by use of an immunoaffinity column made with monoclonal or polyclonal antibodies spedfic for full- length C. felis GluCl channel protein, or polypeptide fragments of C. felis GluCl channel protein. Additionally, polyclonal or monoclonal antibodies may be raised against a synthetic peptide (usually from about 9 to about 25 amino adds in length) from a portion of the protein as disclosed in SEQ ID NO:2. Monospedfic antibodies to C. felis GluCl channel are purified from mammalian antisera containing antibodies reactive against a C. felis GluCl channel or are prepared as monoclonal antibodies reactive with aC. felis GluCl channel using the technique of Kohler and Milstein (1975, Nature 256: 495-497). Monospedfic antibody as used herein is defined as a single antibody spedes or multiple antibody species with homogenous binding characteristics for aC. felis GluCl channel. Homogenous binding as used herein refers to the ability of the antibody spedes to bind to a spedfic antigen or epitope, such as those associated with a C. felis GluCl channel, as described above. C. felis GluCl channel protein-specific antibodies are raised by immunizing animals such as mice, rats, guinea pigs, rabbits, goats, horses and the like, with an appropriate concentration of C. felis GluCl channel protein or a synthetic peptide generated from a portion of C. felis GluCl channel with or without an immune adjuvant. Therefore, the present invention also relates to polyclonal and monoclonal antibodies raised in response to the C. felis GluCl channel protein disclosed herein, or a biologically active fragment thereof. Preimmune serum is collected prior to the first immunization. Each animal receives between about 0.1 μg and about 1000 μg of C. felis GluCl channel protein assodated with an acceptable immune adjuvant. Such acceptable adjuvants include, but are not limited to, Freund's complete, Freund's incomplete, alum-predpitate, water in oil emulsion containing Corynebacterium parvum and tRNA. The initial immunization consists of C. felis GluCl channel protein or peptide fragment thereof in, preferably, Freund's complete adjuvant at multiple sites either subcutaneously (SC), intraperitoneally (IP) or both. Each animal is bled at regular intervals, preferably weekly, to determine antibody titer. The animals may or may not receive booster injections following the initial immunization. Those animals receiving booster injections are generally given an equal amount of C. felis GluCl channel in Freund's incomplete adjuvant by the same route. Booster injections are given at about three week intervals until maximal titers are obtained. At about 7 days after each booster immunization or about weekly after a single immunization, the animals are bled, the serum collected, and aliquots are stored at about -20°C. Monoclonal antibodies (mAb) reactive with C. felis GluCl channel are prepared by immunizing inbred mice, preferably Balb/c, with C. felis GluCl channel protein. The mice are immunized by the IP or SC route with about 1 μg to about 100 μg, preferably about 10 μg, of C. felis GluCl channel protein in about 0.5 ml buffer or saline incorporated in an equal volume of an acceptable adjuvant, as discussed above. Freund's complete adjuvant is preferred. The mice receive an initial immunization on day 0 and are rested for about 3 to about 30 weeks. Immunized mice are given one or more booster immunizations of about 1 to about 100 μg of C. felis GluCl channel protein in a buffer solution such as phosphate buffered saline by the intravenous (IV) route. Lymphocytes, from antibody positive mice, preferably splenic lymphocytes, are obtained by removing spleens from immunized mice by standard procedures known in the art. Hybridoma cells are produced by mixing the splenic lymphocytes with an appropriate fusion partner, preferably myeloma cells, under conditions which will allow the formation of stable hybridomas. Fusion partners may include, but are not limited to: mouse myelomas P3/NSl/Ag 4-1; MPC-11; S-194 and Sp 2/0, with Sp 2/0 being preferred. The antibody produdng cells and myeloma cells are fused in polyethylene glycol, about 1000 mol. wt., at concentrations from about 30% to about 50%. Fused hybridoma cells are selected by growth in hypoxanthine, thymidine and aminopterin supplemented Dulbecco's Modified Eagles Medium (DMEM) by procedures known in the art. Supernatant fluids are collected form growth positive wells on about days 14, 18, and 21 and are screened for antibody production by an immunoassay such as solid phase immunoradioassay (SPIRA) using C. felis GluCl channel protein as the antigen. The culture fluids are also tested in the Ouchterlony precipitation assay to determine the isotype of the mAb. Hybridoma cells from antibody positive wells are cloned by a technique such as the soft agar technique of MacPherson, 1973, Soft Agar Techniques, in Tissue Culture Methods and Applications, Kruse and Paterson, Eds., Academic Press. Monoclonal antibodies are produced in vivo by injection of pristine primed Balb/c mice, approximately 0.5 ml per mouse, with about 2 x 10 6 to about 6 x 10 6 hybridoma cells about 4 days after priming. Ascites fluid is collected at approximately 8-12 days after cell transfer and the monoclonal antibodies are purified by techniques known in the art. In vitro production of anti-C felis GluCl channel protien mAb is carried out by growing the hybridoma in DMEM containing about 2% fetal calf serum to obtain suffident quantities of the spedfic mAb. The mAb are purified by techniques known in the art. Antibody titers of asdtes or hybridoma culture fluids are determined by various serological or immunological assays which include, but are not limited to, predpitation, passive agglutination, enzyme-linked immunosorbent antibody (ELISA) technique and radioimmunoassay (RIA) techniques. Similar assays are used to detect the presence of C. felis GluCl channel protein in body fluids or tissue and cell extracts. It is readily apparent to those skilled in the art that the above described methods for producing monospedfic antibodies may be utilized to produce antibodies specific for C. felis GluCl channel peptide fragments, or full-length C. felis GluCl channel protein. C. felis GluCl channel antibody affinity columns are made, for example, by adding the antibodies to Affigel-10 (Biorad), a gel support which is pre-activated with N-hydroxysuccinimide esters such that the antibodies form covalent linkages with the agarose gel bead support. The antibodies are then coupled to the gel via amide bonds with the spacer arm. The remaining activated esters are then quenched with 1M ethanolamine HC1 (pH 8). The column is washed with water followed by 0.23 M glydne HC1 (pH 2.6) to remove any non-conjugated antibody or extraneous protein. The column is then equilibrated in phosphate buffered saline (pH 7.3) and the cell culture supernatants or cell extracts containing full-length C. felis GluCl channel protein or C. felis GluCl channel protein fragments are slowly passed through the column. The column is then washed with phosphate buffered saline until the optical density (A 2 go) falls to background, then the protein is eluted with 0.23 M glycine-HCl (pH 2.6). The purified C. felis GluCl channel protein is then dialyzed against phosphate buffered saline. Levels of C. felis GluCl channel protein in host cells is quantified by a variety of techniques including, but not limited to, immunoaffinity and/or ligand affinity techniques. C. felis GluCl channel protein-specific affinity beads or C. felis GluCl channel protein - specific antibodies are used to isolate 35 S-methionine labeled or unlabelled C. felis GluCl channel protein. Labeled C. felis GluCl channel protein is analyzed by SDS-PAGE. Unlabelled C. felis GluCl channel protein is detected by Western blotting, ELISA or RIA assays employing C. felis GluCl channel protein specific antibodies. Following expression of C. felis GluCl channel protein in a host cell, C. felis GluCl channel protein may be recovered to provide C. felis GluCl channel protein in active form. Several C. felis GluCl channel protein purification procedures are available and suitable for use. Recombinant C. felis GluCl channel protein may be purified from cell lysates and extracts, or from conditioned culture medium, by various combinations of, or individual application of salt fractionation, ion exchange chromatography, size exclusion chromatography, hydroxylapatite adsorption chromatography and hydrophobic interaction chromatography. It is also possible to prepare membrane preparations from a recombinant host cell which contains a recombinant vector which expresses an active C. felis GluCl channel. Such membrane preparations from recombinant cells will be useful for in vitro-haseά screening assays for compounds which modulate C. felis GluCl channel activity. Compounds identified according to the methods disclosed herein may be used alone at appropriate dosages defined by routine testing in order to obtain optimal inhibition of the GluCl receptor or its activity while minimizing any potential toxicity. In addition, co- administration or sequential administration of other agents may be desirable. The method of the present invention also has the objective of providing suitable topical, oral, systemic and parenteral pharmaceutical formulations for use in the novel methods of treatment of the present invention. The compositions containing compounds identified according to this invention as the active ingredient for use in the modulation of GluCl receptors can be administered in a wide variety of therapeutic dosage forms in conventional vehicles for administration. For example, the compounds can be administered in such oral dosage forms as tablets, capsules (each including timed release and sustained release formulations), pills, powders, granules, elixirs, tinctures, solutions, suspensions, syrups and emulsions, or by injection. Likewise, they may also be administered in intravenous (both bolus and infusion), intraperitoneal, subcutaneous, topical with or without occlusion, or intramuscular form, all using forms well known to those of ordinary skill in the pharmaceutical arts. An effective but non- toxic amount of the compound desired can be employed as a GluCl modulating agent. The daily dosage of the products may be varied over a wide range from 0.001 to 1,000 mg per patient, per day. For oral administration, the compositions are preferably provided in the form of scored or unscored tablets containing 0.01, 0.05, 0.1, 0.5, 1.0, 2.5, 5.0, 10.0, 15.0, 25.0, and 50.0 milligrams of the active ingredient for the symptomatic adjustment of the dosage to the patient to be treated. An effective amount of the drug is ordinarily supplied at a dosage level of from about 0.0001 mg/kg to about 100 mg/kg of body weight per day. The dosages of the GluCl receptor modulators are adjusted when combined to achieve desired effects. On the other hand, dosages of these various agents may be independently optimized and combined to achieve a synergistic result wherein the pathology is reduced more than it would be if either agent were used alone. Advantageously, compounds active in the method of the present invention may be administered in a single daily dose, or the total daily dosage may be administered in divided doses of two, three or four times daily. Furthermore, compounds active in the method of the present invention can be administered in intranasal form via topical use of suitable intranasal vehicles, or via transdermal routes, using those forms of transdermal skin patches well known to those of ordinary skill in that art. To be administered in the form of a transdermal delivery system, the dosage administration will, of course, be continuous rather than intermittent throughout the dosage regimen. For combination treatment with more than one active agent, where the active agents are in separate dosage formulations, the active agents can be administered concurrently, or they each can be administered at separately staggered times. The dosage regimen utilizing the compounds active in the method of the present invention is selected in accordance with a variety of factors including type, species, age, weight, sex and medical condition of the patient; the severity of the condition to be treated; the route of administration; the renal and hepatic function of the patient; and the particular compound thereof employed. A physidan or veterinarian of ordinary skill can readily determine and prescribe the effective amount of the drug required to prevent, counter or arrest the progress of the condition. Optimal precision in achieving concentrations of drug within the range that yields efficacy without toxidty requires a regimen based on the kinetics of the drug's availability to target sites. This involves a consideration of the distribution, equilibrium, and elimination of a drug. MISSING AT THE TIME OF PUBLICATION MISSING AT THE TIME OF PUBLICATION MISSING AT THE TIME OF PUBLICATION The compounds active in the method disclosed herein are also useful against endo and ecto parasites which cause parasitic diseases in humans. Examples of such endoparasites which infect man include gastro-intestinal parasites of the genera Ancylostoma, Necator, Ascaris, Strongy hides, Trichinella, Capillaria, Trichuris, Enterobius, and the like. Other endoparasites which infect man are found in the blood or in other organs. Examples of such parasites are the filarial worms Wucheria, Brugia, Onchocerca, and the like as well as extra- intestinal stages of the intestinal worms Strongylides and Trichinella. Ectoparasites which parasitize man include arthropods such as ticks, fleas, mites, lice, and the like and, as with domestic animals, infections by these parasites can result in transmission of serious and even fatal diseases. The active compounds are active against these endo and ecto parasites and in addition are also active against biting insects and other dipterous pests which annoy humans. The compounds active in the method disclosed herein are also useful against common household pests such as Blatella sp. (cockroach), Tineola sp. (clothes moth), Attagenus sp. (carpet beetle), Musca domestica (housefly) and against Solenopsis Invicta (imported fire ant). The compounds active in the method disclosed herein are furthermore useful against agricultural pests such as aphids (Acyrthiosiphon sp. ), locusts, spider mites, and boll weevils as well as against insect pests which attack stored grains such as Tribolium sp. and Tenebrio sp., and against immature stages of insects living on plant tissue. The compounds are also useful as a nematodidde for the control of soil nematodes and plant parasites such as Meloidogyne sp., which may be agriculturally important. For use as an antiparasitic agent in animals the compounds may be administered internally either orally, or by injection, or topically as a liquid drench or as a shampoo. For oral administration, the compounds active in the method disclosed herein may be administered in capsule, tablet, or bolus form or alternatively they can be mixed in the animals feed. The capsules, tablets, and boluses are comprised of the active ingredient in combination with an appropriate carrier vehicle such as starch, talc, magnesium stearate, or di-caldum phosphate. These unit dosage forms are prepared by intimately mixing the active ingredient with suitable finely-powdered inert ingredients including diluents, fillers, disintegrating agents, and/or binders such that a uniform mixture is obtained. An inert ingredient is one that will not react with the compounds and which is non-toxic to the animal being treated. Suitable inert ingredients include starch, lactose, talc, magnesium stearate, vegetable gums and oils, and the like. These formulations may contain a widely variable amount of the active and inactive ingredients depending on numerous factors such as the size and type of the animal spedes to be treated and the type and severity of the infection. The active ingredient may also be administered as an additive to the feed by simply mixing the compound with the feedstuff or by applying the compound to the surface of the feed. Alternatively the active ingredient may be mixed with an inert carrier and the resulting composition may then either be mixed with the feed or fed directly to the animal. Suitable inert carriers include corn meal, dtrus meal, fermentation residues, soya grits, dried grains and the like. The active ingredients are intimately mixed with these inert carriers by grinding, stirring, milling, or tumbling such that the final composition contains from 0.001 to 5% by weight of the active ingredient. The compounds active in the method disclosed herein may alternatively be administered parenterally via injection of a formulation consisting of the active ingredient dissolved in an inert liquid carrier. Injection may be either intramuscular, intraruminal, intratracheal, or subcutaneous. The injectable formulation consists of the active ingredient mixed with an appropriate inert liquid carrier. Acceptable liquid carriers include the vegetable oils such as peanut oil, cotton seed oil, sesame oil and the like as well as organic solvents such as solketal, glycerol formal and the like. As an alternative, aqueous parenteral formulations may also be used. The vegetable oils are the preferred liquid carriers. The formulations are prepared by dissolving or suspending the active ingredient in the liquid carrier such that the final formulation contains from 0.005 to 10% by weight of the active ingredient. Topical application of the compounds active in the method disclosed herein is possible through the use of a liquid drench or a shampoo containing the instant compounds as an aqueous solution, dispersion or suspension. These formulations generally contain a suspending agent such as bentonite, a wetting agent or the like exdpient, and normally will also contain an antifoaming agent. Formulations containing from 0.001 to 1% by weight of the active ingredient are acceptable. Preferred formulations are those containing from 0.01 to 1% by weight of the active compounds. The compounds active in the method disclosed herein are primarily useful as antiparasitic agents for the treatment and/or prevention of helminthiasis in domestic animals such as cattle, sheep, horses, dogs, cats, goats, swine, and poultry. They are also useful in the prevention and treatment of parasitic infections of these animals by ectoparasites such as ticks, mites, lice, fleas and the like. They are also effective in the treatment of parasitic infections of humans. In treating such infections the compounds may be used individually or in combination with each other or with other unrelated antiparasitic agents. The dosage of the compounds required for best results depends on several factors such as the spedes and size of the animal, the type and severity of the infection, the method of administration and the compound used. Oral administration of the compounds at a dose level of from 0.0005 to 10 mg per kg of animal body weight, either in a single dose or in several doses spaced a few days apart, generally gives good results. A single dose of one of the compounds normally gives excellent control however repeat doses may be given to combat re-infection or for parasite spedes which are unusually persistent. The techniques for administering these compounds to animals are known to those skilled in the veterinary field. The compounds active in the method disclosed herein may also be used to combat agricultural pests which attack crops either in the field or in storage. The compounds are applied for such uses as sprays, dusts, emulsions and the like either to the growing plants or the harvested crops. The techniques for applying these compounds in this manner are known to those skilled in the agricultural arts. Pharmaceutically useful compositions comprising modulators of the C. felis GluCl channel may be formulated according to known methods such as by the admixture of a pharmaceutically acceptable carrier. Examples of such carriers and methods of formulation may be found in Remington's Pharmaceutical Sciences. The term "chemical derivative" describes a molecule that contains additional chemical moieties which are not normally a part of the base molecule. Such moieties may improve the solubility, half-life, absorption, etc. of the base molecule. Alternatively the moieties may attenuate undesirable side effects of the base molecule or decrease the toxicity of the base molecule. Examples of such moieties are described in a variety of texts, such as Remington's Pharmaceutical Sdences. The present invention is also directed to methods for screening for compounds which modulate the expression of DNA or RNA encoding C. felis GluCl as well as the function of the C. felis GluCl protein in vivo. Compounds which modulate these activities may be DNA, RNA, peptides, proteins, or non-proteinaceous organic molecules. Compounds may modulate by increasing or attenuating the expression of DNA or RNA encoding C. felis GluCl, or the function of the C. felis GluCl protein. Compounds that modulate the expression of DNA or RNA encoding C. felis GluCl or the function of C. felis GluCl protein may be detected by a variety of assays. The assay may be a simple "yes/no" assay to determine whether there is a change in expression or function. The assay may be made quantitative by comparing the expression or function of a test sample with the levels of expression or function in a standard sample. Modulators identified in this process are useful as therapeutic agents, insectiddes and anthelminthics. Kits containing C. felis GluCl DNA, antibodies to C. felis GluCl, or C. felis GluCl protein may be prepared. Such kits are used to detect DNA which hybridizes to C. felis GluCl DNA or to detect the presence of C. felis GluCl protein or peptide fragments in a sample. Such characterization is useful for a variety of purposes including but not limited to forensic analyses and epidemiological studies. The DNA molecules, RNA molecules, recombinant protein and antibodies of the present invention may be used to screen and measure levels of C. felis GluCl DNA, RNA or protein. The recombinant proteins, DNA molecules, RNA molecules and antibodies lend themselves to the formulation of kits suitable for the detection and typing of C. felis GluCl. Such a kit would comprise a compartmentalized carrier suitable to hold in close confinement at least one container. The carrier would further comprise reagents such as recombinant C. felis GluCl protein or anti-GluCl antibodies suitable for detecting GluCl. The carrier may also contain a means for detection such as labeled antigen or enzyme substrates or the like. Nucleotide sequences that are complementary to the C. felis GluCl encoding DNA sequence can be synthesized for antisense therapy. These antisense molecules may be DNA, stable derivatives of DNA such as phosphorothioates or methylphosphonates, RNA, stable derivatives of RNA such as 2'-0-alkylRNA, or other GluCl antisense oligonucleotide mimetics. C. felis GluCl antisense molecules may be introduced into cells by microinjection, liposome encapsulation or by expression from vectors harboring the antisense sequence. C. felis GluCl antisense therapy may be particularly useful for the treatment of diseases where it is beneficial to reduce GluCl activity. C. felis GluCl DNA may be used to introduce GluCl into the cells of target organisms. The GluCl gene can be ligated into viral vectors which mediate transfer of the GluCl DNA by infection of redpient host cells. Suitable viral vectors include retrovirus, adenovirus, adeno-associated virus, herpes virus, vaccinia virus, polio virus and the like. Alternatively, GluCl DNA can be transferred into cells by non-viral techniques including receptor-mediated targeted DNA transfer using ligand-DNA conjugates or adenovirus-ligand-DNA conjugates, lipofection membrane fusion or direct microinjection. These procedures and variations thereof are suitable for ex vivo as well as in vivo GluCl gene therapy. GluCl gene therapy may be particularly useful where it is benefϊάal to elevate GluCl activity. The present invention also provides for improved methods of screening for modulators of a GluCl channel in general and modulators of the C. felis GluCl channel in particular. It is shown in Example Section 2 that improved assay conditions result in a 10-fold increase in channel modulator sensitivity when compared to previous known assay conditions. In a preferred aspect of measuring GluCl channel adtivity, oocytes are injected with synthetic RNAs or DNAs for one or more C. felis GluCl proteins. Following an appropriate period of time to allow for expression, GluCl activity is measured by specific ligand binding and electrophysiological characteristics of the host cells expressing GluCl DNA. Voltage-clamp studies were conducted as described in Example Section 2, preferably utilizing a holding potential of 0 mV during measurements of modulation by ivermectin phosphate. Exemplification of this improved method of a cell-based assay of GluCl channel activity is shown in Example Section 2 and is futher detailed in Figures 5A and 5B (showing activation of CfGluCl-1 by glutamate), Figure 6 (showing that the CfGluCl-1 channel is selective for chloride), and Figures 7A and 7B (showing that IVM-PO 4 is an agonist of a GluCl channel). The following examples are provided to illustrate the present invention without, however, limiting the same hereto. EXAMPLE 1: Isolation and Characterization of a Full Length cDNA Encoding a Ctenocephalides felis GluCl Channel Ctenocephalides felis Poly A + RNA isolation - Poly(A) + RNA was prepared from whole fleas. The fleas were rapidly frozen in liquid N2 and ground with a mortar and pestle while submerged in liquid N2- The frozen, powdered C. felis tissue was added to a solution containing 4M guanidinium thiocyanate, 5mM sodium dtrate pH 7.0, and 0.1 M β- mercapto ethanol (lgm tissue/10 ml solution), and was mixed with a polytron homogenizer. After 1 minute of homogenization, 0.5% sodium sarkosyl was added and mixed well and the solution was centrifuged at 10,000 rpm for 10 minutes. The supernatant was layered over a 5.7 M CsCl cushion and centrifuged for 18 hours at 33,000 rpm. The RNA pellet was washed with 70% ethanol, resuspended in H2O and extracted with chloroform sobutanol, 4:1 and predpitated with ethanol. Poly (A)+ RNA was isolated by two rounds of purification on oligo (dT)-cellulose columns. Isolation of a cDNA Partially Encoding a C.felis GluCl Channel - An oligo-dT primed C. felis cDNA library was prepared in the phagemid cloning vector λZAPII (Stratagene, LaJolla, CA) This library was transfected into E. coli PLK-F * cells, plated on NZY medium (Sambrook, et al, 1989, Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY), and incubated 18 hrs. at 37°C. The resultant plaques were transferred to Durulose membranes (Stratagene). The membranes were prehybridized in 50% formamide; 2x Denhardts solution; 5x SSPE; 0.1%SDS; lOOμg/ml solmon sperm DNA for 16 hours and hybridized in the above prehybridization solution containing 10% dextran sulfate for 24 hours with 2x10 cpm a hybridization probe was a PCR-generated fragment of the DrosGluCl cDNA corresponding to nucleotides 471-1760 of the cDNA as listed in GenBank (Cully, et al., 1996, J. Biol. Chem. 271(33): 20187-20191; accession number U58776). This DNA codes for all but the last four amino acids of the mature Drosophila glutamate-gated chloride channel. The filters were washed at 52°C in 6xSSC, 0.1% SDS. The washed filiters were exposed to X-ray film. Two positive clones, F5A and F6 were chosen for further analysis. These clones were converted into plasmids by in vivo exdsion as per the Stratagene protocol. Clone F5A was subjected to DNA sequence analysis and is disclosed in Figure 3 and SEQ ID NO:3, and as follows: ATGGACAGCA TTAGTTTGCT CCTACTTTTG ATAACATGTC TAAGTCTACA CACATGCTTA TCTGCAAATG CAAAACCTCG TCTAGGAGGC GGCAAAGAAA ATTTCAGGGC CAAAGAAAAG CAAGTTCTGG ACCAAATTTT AGGCCCAGGC CATTACGATG CCAGAATAAG GCCTTCTGGA GTCAATGGAA CTGGAATACA GTGTCCAGTT AACTTTCAGG GAACAATGGC AGGATGAGAG GTTGAAATTT AACGACTTTG GAGGTCGTTT AAAATACTTA ACACTAACCG AAGCAAGTCG TGTATGGATG CCCGATTTGT TCTTTGCGAA TGAAAAGGAG GGCCACTTTC ACAACATCAT CATGCCGAAC GTCTACATTC GTATTTTTCC TTACGGTTCC GTACTATACA GCATCAGGAT ATCGCTTACT TTGGCGTGTC CTATGAATCT GAAACTGTAT CCGCTCGATA GGCAGGTGTG CTCTCTCCGG ATGGCCAGTT ATGGTTGGAC CACAAACGAT CTGGTGTTTT TGTGGAAGGA AGGTGACCCG GTGCAGGTTG TCAAGAATCT ACATCTGCCC AGGTTTACGT TGGAGAAGTT CTTGACGGAT TATTGTAACA GCAAAACCAA TACCGGTGAA TACAGTTGCC TGAAGGTCGA CCTGCTCTTT AAACGAGAGT TCTCGTACTA CCTGATCCAG ATCTACATTC CTTGTTGCAT GTTGGTGATC GTTTCCTGGG TGTCGTTCTG GTTGGACCAG GGAGCGGTTC CGGCCAGAGT ATCACTGGGT GTGACCACTC TCCTCACCAT GGCCACCCAG ACGTCGGGCA TAAACGCCTC CCTGCCGCCA GTGTCCTACA CAAAAGCCAT CGACGTCTGG ACCGGAGTCT GCCTCACGTT CGTCTTCGGG GCTTTGCTCG AATTCGCCCT CGTCAACTAC GCCTCCAGAT CCGATATGCA CAGGGAAAAC ATGAAGAAAA AGCGCAGGGA ACTTGAACAA GCAGCCAGCC TGGACGCCGC CTCCGACCTG ATGGACGGCA CTGATGGCAC TTTTGCTATG AAGCCTCTGG TACGCCACTC CGTCGACGCC GTCGGTCTCG ATAAGGTTCG TCAGTGCGAG ATACACATGC AGCCGGCGTC CAGGCAGAAC TGCTGCAGGA GCTGGATAAG CAAATTCCCG ACGAGGTCGA AACGCATCGA CGTCATATCA AGAATCACTT TCCCGCTGGT GTTTGCTTTG TTCAATCTGG TGTACTGGTC GACCTATTTG TTCAGGGACG AGGCGGAGGA GAATTAG (SEQ ID NO : 3 ) . Clone F5A was shown to encode a truncated polypeptide disclosed in Figure 4 and SEQ ID NO:4, referred to within this spedfication as trCfGluCl-1, and disclosed as follows: 1 MDSISL L L ITCLSLHTCL SANAKPRLGG GKENFRAKEK QVLDQILGPG 51 HYDARIRPSG VNGTGIQCPV NFQGTMAG (SEQ ID NO: 4) . Isolation of a cDNA Encoding a C. felis GluCl Channel - It was determined that clone F5A lacked an internal portion a possible C. felis GluCl channel cDNA at the presumptive amino-terminal extracellular domain, resulting in a frame shift mutation and the concomitant truncated protein, trCfGluCl- 1. A cDNA fragment containing the missing portion of a putative C. felis GluCl channel cDNA was generated by PCR amplification of randomly primed flea cDNA. Primer-1 (CTCAGAGTCAGGATCCGGCTA; SEQ ID NO:5) and Primer-2 (CTGAAAGTTAACTGGACACTG; SEQ ID NO:6) were used in a standard PCR reaction to amplify a 532 bp PCR fragment that was shown by DNA sequence analysis to contain the missing 71 nucleotides and flanking sequences disclosed in the F5A clone. This PCR fragment is as follows: TCAGAGTCA G GATCC GGCTA TATTGGACGA TATGCTGCAT GGTCCCTGTC ATACAAATAC TCCTTCGCCT TCACTGGAAC CAACCAAGAC TGTCCCCACG TGTCCGACAT CAGTTGAAGG AAATTCTGTG ACGACATGGC AACACTTTTG TTCAGGAACA ACAATAACAT CATCGACACA GAATATCGGC GAAGCCTATT CTTCGATTCA AGAAGAAGAA TTTCTTCACT TTATCTTCAG GGATGGACAG CATTAGTTTG CTCCTACTTT TGATAACATG TCTAAGTCTA CACACATGCT TATCTGCAAA TGCAAAACCT CGTCTAGGAG GCGGCAAAGA AAATTTCAGG GCCAAAGAAA AGCAAGTTCT GGACCAAATT TTAGGCCCAG GCCATTACGA TGCCAGAATA AGGCCTTCTG GAGTCAATGG AACTGGAGAC GGTCCGACCG TGGTAGCAGT CAACATCTAT CTGAGATCAA TCAGCGAAAT AGATGACTAC AAAATGGAAT ACAGTGTCCA GTTAAC TTTC AG ( SEQ ID NO : 8 ) This PCR fragment was cloned using the TA cloning vector kit (Invitrogen) and individual clones were sequenced to identify those lacking PCR artifacts and containing the missing 71 bp fragment. A 517 bp BamHI/Hpal fragment (Bam HI-GGATCC; Hpal GTTAAC, as underlined above) of this PCR product was isolated and inserted into a BamHI/Hpal digested F5A clone (Figure 3; SEQ ID NO:3) to generate the full length cDNA clone in the F5A pBS vector, designated Fleaδl, shown in Figure 1, and set forth as SEQ ID NO:l as follows: ATGGACAGCA TTAGTTTGCT CCTACTTTTG ATAACATGTC TAAGTCTACA CACATGCTTA TCTGCAAATG CAAAACCTCG TCTAGGAGGC GGCAAAGAAA ATTTCAGGGC CAAAGAAAAG CAAGTTCTGG ACCAAATTTT AGGCCCAGGC CATTACGATG CCAGAATAAG GCCTTCTGGA GTCAATGGAA CTGGAGACGG TCCGACCGTG GTAGCAGTCA ACATCTATCT GAGATCAATC AGCGAAATAG ATGACTACAA AATGGAATAC AGTGTCCAGT TAACTTTCAG GGAACAATGG CAGGATGAGA GGTTGAAATT TAACGACTTT GGAGGTCGTT TAAAATACTT AACACTAACC GAAGCAAGTC GTGTATGGAT GCCCGATTTG TTCTTTGCGA ATGAAAAGGA GGGCCACTTT CACAACATCA TCATGCCGAA CGTCTACATT CGTATTTTTC CTTACGGTTC CGTACTATAC AGCATCAGGA TATCGCTTAC TTTGGCGTGT CCTATGAATC TGAAACTGTA TCCGCTCGAT AGGCAGGTGT GCTCTCTCCG GATGGCCAGT TATGGTTGGA CCACAAACGA TCTGGTGTTT TTGTGGAAGG AAGGTGACCC GGTGCAGGTT GTCAAGAATC TACATCTGCC CAGGTTTACG TTGGAGAAGT TCTTGACGGA TTATTGTAAC AGCAAAACCA ATACCGGTGA ATACAGTTGC CTGAAGGTCG ACCTGCTCTT TAAACGAGAG TTCTCGTACT ACCTGATCCA GATCTACATT CCTTGTTGCA TGTTGGTGAT CGTTTCCTGG GTGTCGTTCT GGTTGGACCA GGGAGCGGTT CCGGCCAGAG TATCACTGGG TGTGACCACT CTCCTCACCA TGGCCACCCA GACGTCGGGC ATAAACGCCT CCCTGCCGCC AGTGTCCTAC ACAAAAGCCA TCGACGTCTG GACCGGAGTC TGCCTCACGT TCGTCTTCGG GGCTTTGCTC GAATTCGCCC TCGTCAACTA CGCCTCCAGA TCCGATATGC ACAGGGAAAA CATGAAGAAA AAGCGCAGGG AACTTGAACA AGCAGCCAGC CTGGACGCCG CCTCCGACCT GATGGACGGC ACTGATGGCA CTTTTGCTAT GAAGCCTCTG GTACGCCACT CCGTCGACGC CGTCGGTCTC GATAAGGTTC GTCAGTGCGA GATACACATG CAGCCGGCGT CCAGGCAGAA CTGCTGCAGG AGCTGGATAA GCAAATTCCC GACGAGGTCG AAACGCATCG ACGTCATATC AAGAATCACT TTCCCGCTGG TGTTTGCTTT GTTCAATCTG GTGTACTGGT CGACCTATTT GTTCAGGGAC GAGGCGGAGG AGAATTAG (SEQ ID NO : 1 ) . This cDNA molecule contains an open reading frame which encodes a C. felis GluCl channel, as shown in Figure 2, as set forth as SEQ ID NO:2, and as follows: MDSISLLLLL ITCLSLHTCL SANAKPRLGG GKENFRAKEK QVLDQI GPG HYDARIRPSG VNGTGDGPTV VAVNIYLRSI SEIDDYKMEY SVQLTFREQW QDERLKFNDF GGRLKYLTLT EASRVWMPDL FFANEKEGHF HNIIMPNVYI RIFPYGSVLY SIRISLTLAC PMNLKLYPLD RQVCSLRMAS YGWTTNDLVF LWKEGDPVQV VKNLHLPRFT LEKFLTDYCN SKTNTGEYSC LKVDLLFKRE FSYYLIQIYI PCCMLVIVSW VSFWLDQGAV PARVSLGVTT LLTMATQTSG INASLPPVSY TKAIDVWTGV CLTFVFGALL EFALVNYASR SDMHRENMKK KRRELEQAAS LDAASDLMDG TDGTFAMKPL VRHSVDAVGL DKVRQCEIHM QPASRQNCCR SWISKFPTRS KRIDVISRIT FPLVFALFNL VYWSTYLFRD EAEEN (SEQ ID NO : 2 ) . In addition, the 5' untranslated region the exemplified cDNA which encodes a CfGluCl channel protein was determined and is presented as SEQ ID NO:7, and as follows: AACTAGTGGA TCCCCCGGGC TGCAGGATTC GGCACGAGAA TTTTTTAAAA TAATCCTCAA CAGCATGATA CAAGAGGATG ATTTTATGAT CCCTGTAAAC ACTTGCTTGA ATTTTAGATT GCAACTGGAG GCTCCGCTGA CACTCTCTCT TGTTCGAGCA CAGGAATTGC TCGACATCTG GTCAAACGCG GGCTACTTCA TAATATCCGA CGATGACAAT TTAATGTTCG GAGCAAGAAC AATTGCAGAA TTTGAAGTGT ACTTTAACGA TACATTCGAA GGACGCATGA AAATGTGCAC GATGTGCATG TTGCCCACCT TCTATTGACC AGCAAGCACC CCTTCGCCGG TGAGCATGTC ACCCACCGAC AGGCGCCTTC TGTGCGCCCT CGACGACCTG CACTTAGCGG TTGCTAAGAA GCCCTAAGAA GCCGAGACGG TTCGCTTCGC CCGGGGGCGA TTCCTCACGA TGCACAAGCG GAGGCGCAAG AGGCTGACGA CGAGGAGCCT CAGAGTCAGG ATCCGGCTAT ATTGGACGAT ATGCTGCATG GTCCCTGTCA TACAAATACT CCTTCGCCTT CACTGGAACC AACCAAGACT GTCCCCACGT GTCCGACATC AGTTGAAGGA AATTCTGTGA CGACATGGCA ACACTTTTGT TCAGGAACAA CAATAACATC ATCGACACAG AATATCGGCG AAGCCTATTC TTCGATTCAA GAAGAAGAAT TTCTTCACTT TATCTTCAGG G (SEQ ID NO: 7) EXAMPLE 2 Expression of the CfGluCl-1 protein in e opus oocvtes The full-length cDNA encoding CfGluCl- 1 in plasmid vector pBluescript (Stratagene, LaJolla, CA) is linearized and capped cRNA transcripts are synthesiszed using appropriate oligonucleotide primers and the mMESSAGE mMACHINE in vitro RNA transcription kit (Ambion). Xenopus laevis oocytes were prepared and injected using standard methods as described (Arena et al., 1991, Mol Pharmacol. 40: 368-374; Arena et al, 1992, Mol Brain Res. 15: 339-348). Adult female Xenopus laevis were anesthetized with 0.17% tricaine methanesulfonate and the ovaries were surgically removed and placed in a dish consisting of (mM): NaCl 82.5, KC1 2, MgCl2 1, CaCl2 1.8, HEPES 5 adjusted to pH 7.5 with NaOH (OR-2). Ovarian lobes were broken open, rinsed several times, and gently shaken in OR-2 containing 0.2% collagenase (Sigma, Type 1A) for 2-5 hours. When approximately 50% of the follicular layers were removed, Stage V and VI oocytes were selected and placed in media consisting of (mM): NaCl 86, KC1 2, MgCl2 1, CaCl2 1.8, HEPES 5, Na pynivate 2.5, theophylline 0.5, gentamicin 0.1 adjusted to pH 7.5 with NaOH (ND-96) for 24-48 hours before injection. For most experiments, oocytes were injected with 10 ng of cRNA in 50 nl of RNase free water. Control oocytes were injected with 50 nl of water. Oocytes were incubated for 1-5 days in ND-96 supplemented with 50 mg/ml gentamycin, 2.5 mM Na pynivate and 0.5 mM theophylline before recording. Incubations and collagenase digestion were carried out at 18° C. Voltage-clamp studies were conducted with the two microelectrode voltage clamp technique using a Dagan CA1 amplifier (Dagan Instruments, Minneapolis, MN). The current passing microelectrodes were filled with 0.7 M KC1 plus 1.7 M K 3 -citrate and the voltage recording microelectrodes were filled with 1.0 M KC1. The extracellular solution for most experiments was saline consisting of (mM): NaCl 96, BaCl2 3.5, MgCl2 0.5, CaCl2 0.1, HEPES 5, adjusted to pH 7.5 with NaOH. The extracellular chloride concentration was reduced in some experiments by equimolar replacement of NaCl with the sodium salt of the indicated anion. Experiments were conducted at 21-24 ° C Data were acquired using the program Pulse and most analysis was performed with the companion program Pulsefit (Instrutech Instruments, Great Neck, NY) or with Igor Pro (Wavemetrics, Lake Oswego, OR). Data were filtered (fc, -3db) at 1 kHz, unless otherwise indicated. Figure 5 A and Figure 5B show the activation of CfGluCl- 1 by glutamate. Figure 5 A shows superimposed current recordings in response to 10, 30, 100 and 300 μM glutamate. The duration of exposure to glutamate is indicated by the solid bar at top. Figure 5B shoes the concentration-response curve for glutamate. Peak outward current is plotted vs. glutamate concentration. The solid curve is the best fit to the equation I/I max ={ l+(EC5o/[glutamate]) n } _ l . For the experiment shown in Figure 5B, EC50=9.3 μM, n=2.13. Agonists for other types of ligand-gated chloride channels were also tested for the ability to activate CfGluCl-1. GABA, glycine, histamine, acetylcholine and muscimol were all inactive. Figure 6 shows that the CfGluCl- 1 channel is selective for chloride. Each curve represents the difference between the current measured with and without 10 μM glutamate. The voltage was ramped from -120 to +60 mV at 1 volt/second. Chloride concentration was reduced from 104 mM to 8.2 mM by equimolar substitution of NaCl by Na-methanesulfonate or Na-gluconate. Each current-voltage relationship was fit to a seventh order polynomial using non-linear least squares analysis and the reversal potential was taken as the x-intercept of this polynomial. The reversal potential measurements indicate that the relative permeability for methanesulfonate ( i.e., (permeability for methanesulfonate)/ (permeability for chloride)) is 0.218 and the relative permeability for gluconate is 0.064. Figures 7A and B show that ivermectin phosphate is an agonist of the flea GluCl channel encoded by CfGluCl-1. Figure 7A shows activation of CfGluCl- 1 by ivermectin phosphate (IVM-PO 4 ) and superimposed current recordings showing activation by 100 μM glutamate and 10 nM IVM-PO 4 . The activation by IVM-PO4 has a sigmoidal onset suggesting that multiple binding sites must be occupied for opening. Figure 7B shows the concentration-response curve for IVM-PO4. A single [IVM-PO4] was tested on each oocyte. The ordinate is the maximal current induced by rVM-PO normalized by the peak current induced by 100 μM glutamate, a maximally effective concentration. The error bars indicate ±S.E.M. The holding potential was 0 mV for both sets of measurements. The filled drcles represent data for CfGluCl- 1. The solid curve is the best fit to this data by (1) I= ,max /U+(EC 50 /[IVM-PO4])n} where Ii vm , ma χ =0.718, EC 50 =2.93 nM, and n=1.0. Also shown is the dose-response curve previously reported for the DmGluCU clone from Drosophila melanogaster , except that in these earlier studies the holding potential was -80 mV (Cully et al., J. 1996, J. Biol. Chem. 271: 20187-20191). This curve is the best fit to equation (1) for modification by IVM-PO4, where Ii V m max =0.35, EC5Q=41 nM, and n=1.2. This data shows a 10-fold increase in potency. Additional data shows that this increase in potency is not the result of differences between the clones and/or in measurement technique. The measurements were repeated on DmGluCU at a holding potential of 0 mV (filled squares); the solid curve is the best fit to equation (1) with the constraint that the EC50 and n are the same as for CfGluCll. The goodness of fit indicates that the EC50 for DmGluCU is similar to that for CfGluCll and that both channels are activated by IVM-PO4 at concentrations 10-fold lower than previously recognized.

Claims: WHAT IS CLAIMED: 1. A purified DNA molecule encoding a C. felis GluClu channel protein wherein said protein comprises the amino acid sequence as follows: MDSISLLLLL ITCLSLHTCL SANAKPRLGG GKENFRAKEK QVLDQILGPG HYDARIRPSG VNGTGDGPTV VAVNIYLRSI SEIDDYKMEY SVQLTFREQW QDERLKFNDF GGRLKYLTLT EASRVWMPDL FFANEKEGHF HNIIMPNVYI RIFPYGSVLY SIRISLTLAC PMNLKLYPLD RQVCSLRMAS YGWTTNDLVF LWKEGDPVQV VKNLHLPRFT LEKFLTDYCN SKTNTGEYSC LKVDLLFKRE FSYYLIQIYI PCCMLVIVSW VSFWLDQGAV PARVSLGVTT LLTMATQTSG INASLPPVSY TKAIDVWTGV CLTFVFGALL EFALVNYASR SDMHRENMKK KRRELEQAAS LDAASDLMDG TDGTFAMKPL VRHSVDAVGL DKVRQCEIHM QPASRQNCCR SWISKFPTRS KRIDVISRIT FPLVFALFNL VYWSTYLFRD EAEEN as set forth in three-letter abbreviation in SEQ ID NO:2. 2. An expression vector for expressing a C. felis GluClu channel protein in a recombinant host cell wherein said expression vector comprises a DNA molecule of claim 1. 3. A host cell which expresses a recombinant C. felis GluClu channel protein wherein said host cell contains the expression vector of claim 2. 4. A process for expressing a C. felis GluClu channel protein in a recombinant host cell, comprising: (a) transfecting the expression vector of claim 2 into a suitable host cell; and, (b) culturing the host cells of step (a) under conditions which allow expression of said C. felis GluClu channel protein from said expression vector. 5. A purified DNA molecule encoding a C. felis GluClu channel protein wherein said protein consisits of the amino acid sequence as follows: MDSISLLLLL ITCLSLHTCL SANAKPRLGG GKENFRAKEK QVLDQILGPG , HYDARIRPSG VNGTGDGPTV VAVNIYLRSI SEIDDYKMEY SVQLTFREQW QDERLKFNDF GGRLKYLTLT EASRVWMPDL FFANEKEGHF HNIIMPNVYI RIFPYGSVLY SIRISLTLAC PMNLKLYPLD RQVCSLRMAS YGWTTNDLVF LWKEGDPVQV VKNLHLPRFT LEKFLTDYCN SKTNTGEYSC LKVDLLFKRE FSYYLIQIYI PCCMLVIVSW VSFWLDQGAV PARVSLGVTT LLTMATQTSG INASLPPVSY TKAIDVWTGV CLTFVFGALL EFALVNYASR SDMHRENMKK KRRELEQAAS LDAASDLMDG TDGTFAMKPL VRHSVDAVGL DKVRQCEIHM QPASRQ CCR SWISKFPTRS KRIDVISRIT FPLVFALFNL VYWSTYLFRD EAEEN/ as set forth in three-letter abbreviation in SEQ ID NO:2. 6. An expression vector for expressing a C. felis GluClu channel protein in a recombinant host cell wherein said expression vector comprises a DNA molecule of claim 5. 7. A host cell which expresses a recombinant C. felis GluClu channel protein wherein said host cell contains the expression vector of claim 6. 8. A process for expressing a C. felis GluClu channel protein in a recombinant host cell, comprising: (a) transfecting the expression vector of claim 6 into a suitable host cell; and, (b) culturing the host cells of step (a) under conditions which allow expression of said C. felis GluClu channel protein from said expression vector. 9. A purified DNA molecule encoding a recombinant C. felis GluClu channel protein wherein said DNA molecule comprises the nucleotide sequence as set forth in SEQ ID NO:l, as follows: ATGGACAGCA TTAGTTTGCT CCTACTTTTG ATAACATGTC TAAGTCTACA CACATGCTTA TCTGCAAATG CAAAACCTCG TCTAGGAGGC GGCAAAGAAA ATTTCAGGGC CAAAGAAAAG CAAGTTCTGG ACCAAATTTT AGGCCCAGGC CATTACGATG CCAGAATAAG GCCTTCTGGA GTCAATGGAA CTGGAGACGG TCCGACCGTG GTAGCAGTCA ACATCTATCT GAGATCAATC AGCGAAATAG ATGACTACAA AATGGAATAC AGTGTCCAGT TAACTTTCAG GGAACAATGG CAGGATGAGA GGTTGAAATT TAACGACTTT GGAGGTCGTT TAAAATACTT AACACTAACC GAAGCAAGTC GTGTATGGAT GCCCGATTTG TTCTTTGCGA ATGAAAAGGA GGGCCACTTT CACAACATCA TCATGCCGAA CGTCTACATT CGTATTTTTC CTTACGGTTC CGTACTATAC AGCATCAGGA TATCGCTTAC TTTGGCGTGT CCTATGAATC TGAAACTGTA TCCGCTCGAT AGGCAGGTGT GCTCTCTCCG GATGGCCAGT TATGGTTGGA CCACAAACGA TCTGGTGTTT TTGTGGAAGG AAGGTGACCC GGTGCAGGTT GTCAAGAATC TACATCTGCC CAGGTTTACG TTGGAGAAGT TCTTGACGGA TTATTGTAAC AGCAAAACCA ATACCGGTG ATACAGTTGC CTGAAGGTCG ACCTGCTCTT TAAACGAGAG TTCTCGTACT ACCTGATCCA GATCTACATT CCTTGTTGCA TGTTGGTGAT CGTTTCCTGG GTGTCGTTCT GGTTGGACCA GGGAGCGGTT CCGGCCAGAG TATCACTGGG TGTGACCACT CTCCTCACCA TGGCCACCCA GACGTCGGGC ATAAACGCCT CCCTGCCGCC AGTGTCCTAC ACAAAAGCCA TCGACGTCTG GACCGGAGTC TGCCTCACGT TCGTCTTCGG GGCTTTGCTC GAATTCGCCC TCGTCAACTA CGCCTCCAGA TCCGATATGC ACAGGGAAAA CATGAAGAAA AAGCGCAGGG AACTTGAACA AGCAGCCAGC CTGGACGCCG CCTCCGACCT GATGGACGGC ACTGATGGCA CTTTTGCTAT GAAGCCTCTG GTACGCCACT CCGTCGACGC CGTCGGTCTC GATAAGGTTC GTCAGTGCGA GATACACATG CAGCCGGCGT CCAGGCAGAA CTGCTGCAGG AGCTGGATAA GCAAATTCCC GACGAGGTCG AAACGCATCG ACGTCATATC AAGAATCACT TTCCCGCTGG TGTTTGCTTT GTTCAATCTG GTGTACTGGT CGACCTATTT GTTCAGGGAC GAGGCGGAGG AGAATTAG, (SEQ ID NO : 1) . 10. An expression vector for expressing a recombinant C. felis GluClu channel protein wherein said expression vector comprises a DNA molecule of claim 9. 11. A host cell which expresses a recombinant recombinant C. felis GluClu channel protein wherein said host cell contains the expression vector of claim 10. 12. A process for expressing a recombinant C. felis GluClu channel protein in a recombinant host cell, comprising: (a) transfecting the expression vector of claim 10 into a suitable host cell; and, (b) culturing the host cells of step (a) under conditions which allow expression of said recombinant C. felis GluClu channel protein from said expression vector. 13. A purified DNA molecule encoding a recombinant C. felis GluClu channel protein wherein said DNA molecule consists of the nucleotide sequence as set forth in SEQ ID NO:l, as follows: ATGGACAGCA TTAGTTTGCT CCTACTTTTG ATAACATGTC TAAGTCTACA CACATGCTTA TCTGCAAATG CAAAACCTCG TCTAGGAGGC GGCAAAGAAA ATTTCAGGGC CAAAGAAAAG CAAGTTCTGG ACCAAATTTT AGGCCCAGGC CATTACGATG CCAGAATAAG GCCTTCTGGA GTCAATGGAA CTGGAGACGG TCCGACCGTG GTAGCAGTCA ACATCTATCT GAGATCAATC AGCGAAATAG ATGACTACAA AATGGAATAC AGTGTCCAGT TAACTTTCAG GGAACAATGG CAGGATGAGA GGTTGAAATT TAACGACTTT GGAGGTCGTT TAAAATACTT AACACTAACC GAAGCAAGTC GTGTATGGAT GCCCGATTTG TTCTTTGCGA ATGAAAAGGA GGGCCACTTT CACAACATCA TCATGCCGAA CGTCTACATT CGTATTTTTC CTTACGGTTC CGTACTATAC AGCATCAGGA TATCGCTTAC TTTGGCGTGT CCTATGAATC TGAAACTGTA TCCGCTCGAT AGGCAGGTGT GCTCTCTCCG GATGGCCAGT TATGGTTGGA CCACAAACGA TCTGGTGTTT TTGTGGAAGG AAGGTGACCC GGTGCAGGTT GTCAAGAATC TACATCTGCC CAGGTTTACG TTGGAGAAGT TCTTGACGGA TTATTGTAAC AGCAAAACCA ATACCGGTGA ATACAGTTGC CTGAAGGTCG ACCTGCTCTT TAAACGAGAG TTCTCGTACT ACCTGATCCA GATCTACATT CCTTGTTGCA TGTTGGTGAT CGTTTCCTGG GTGTCGTTCT GGTTGGACCA GGGAGCGGTT CCGGCCAGAG TATCACTGGG TGTGACCACT CTCCTCACCA TGGCCACCCA GACGTCGGGC ATAAACGCCT CCCTGCCGCC AGTGTCCTAC ACAAAAGCCA TCGACGTCTG GACCGGAGTC TGCCTCACGT TCGTCTTCGG GGCTTTGCTC GAATTCGCCC TCGTCAACTA CGCCTCCAGA TCCGATATGC ACAGGGAAAA CATGAAGAAA AAGCGCAGGG AACTTGAACA AGCAGCCAGC CTGGACGCCG CCTCCGACCT GATGGACGGC ACTGATGGCA CTTTTGCTAT GAAGCCTCTG GTACGCCACT CCGTCGACGC CGTCGGTCTC GATAAGGTTC GTCAGTGCGA GATACACATG CAGCCGGCGT CCAGGCAGAA CTGCTGCAGG AGCTGGATAA GCAAATTCCC GACGAGGTCG AAACGCATCG ACGTCATATC AAGAATCACT TTCCCGCTGG TGTTTGCTTT GTTCAATCTG GTGTACTGGT CGACCTATTT GTTCAGGGAC GAGGCGGAGG AGAATTAG, (SEQ ID NO: 1 ) . 14. An expression vector for expressing a recombinant C. felis GluClu channel protein wherein said expression vector comprises a DNA molecule of claim 13. 15. A host cell which expresses a recombinant recombinant C. felis GluClu channel protein wherein said host cell contains the expression vector of claim 14. 16. A process for expressing a recombinant C. felis GluClu channel protein in a recombinant host cell, comprising: (a) transfecting the expression vector of claim 14 into a suitable host cell; and, (b) culturing the host cells of step (a) under conditions which allow expression of said recombinant C. felis GluClu channel protein from said expression vector. 17. A purified DNA molecule encoding a truncated portion of aC. felis GluClu channel protein wherein said protein consisits of the amino add sequence as follows: MDSISLLLLL ITCLSLHTCL SANAKPRLGG GKENFRAKEK QVLDQILGPG HYDARIRPSG VNGTGIQCPV NFQGTMAG / as set forth in three-letter abbreviation in SEQ ID NO:4. 18. An expression vector for expressing a C. felis GluClu channel protein in a recombinant host cell wherein said expression vector comprises a DNA molecule of claim 17. 19. A host cell which expresses a recombinant C. felis GluClu channel protein wherein said host cell contains the expression vector of claim 18. 20. A process for expressing a C. felis GluClu channel protein in a recombinant host cell, comprising: (a) transfecting the expression vector of claim 18 into a suitable host cell; and, (b) culturing the host cells of step (a) under conditions which allow expression of said C. felis GluClu channel protein from said expression vector. 21. A purified DNA molecule encoding a recombinant C. felis GluClu channel protein wherein said DNA molecule consists of the nucleotide sequence as set forth in SEQ ID NO:3, as follows: ATGGACAGCA TTAGTTTGCT CCTACTTTTG ATAACATGTC TAAGTCTACA CACATGCTTA TCTGCAAATG CAAAACCTCG TCTAGGAGGC GGCAAAGAAA ATTTCAGGGC CAAAGAAAAG CAAGTTCTGG ACCAAATTTT AGGCCCAGGC CATTACGATG CCAGAATAAG GCCTTCTGGA GTCAATGGAA CTGGAATACA GTGTCCAGTT AACTTTCAGG GAACAATGGC AGGATGAGAG GTTGAAATTT AACGACTTTG GAGGTCGTTT AAAATACTTA ACACTAACCG AAGCAAGTCG TGTATGGATG CCCGATTTGT TCTTTGCGAA TGAAAAGGAG GGCCACTTTC ACAACATCAT CATGCCGAAC GTCTACATTC GTATTTTTCC TTACGGTTCC GTACTATACA GCATCAGGAT ATCGCTTACT TTGGCGTGTC CTATGAATCT GAAACTGTAT CCGCTCGATA GGCAGGTGTG CTCTCTCCGG ATGGCCAGTT ATGGTTGGAC CACAAACGAT CTGGTGTTTT TGTGGAAGGA AGGTGACCCG GTGCAGGTTG TCAAGAATCT ACATCTGCCC AGGTTTACGT TGGAGAAGTT CTTGACGGAT TATTGTAACA GCAAAACCAA TACCGGTGAA TACAGTTGCC TGAAGGTCGA CCTGCTCTTT AAACGAGAGT TCTCGTACTA CCTGATCCAG ATCTACATTC CTTGTTGCAT GTTGGTGATC GTTTCCTGGG TGTCGTTCTG GTTGGACCAG GGAGCGGTTC CGGCCAGAGT ATCACTGGGT GTGACCACTC TCCTCACCAT GGCCACCCAG ACGTCGGGCA TAAACGCCTC CCTGCCGCCA GTGTCCTACA CAAAAGCCAT CGACGTCTGG ACCGGAGTCT GCCTCACGTT CGTCTTCGGG GCTTTGCTCG AATTCGCCCT CGTCAACTAC GCCTCCAGAT CCGATATGCA CAGGGAAAAC ATGAAGAAAA AGCGCAGGGA ACTTGAACAA GCAGCCAGCC TGGACGCCGC CTCCGACCTG ATGGACGGCA CTGATGGCAC TTTTGCTATG AAGCCTCTGG TACGCCACTC CGTCGACGCC GTCGGTCTCG ATAAGGTTCG TCAGTGCGAG ATACACATGC AGCCGGCGTC CAGGCAGAAC TGCTGCAGGA GCTGGATAAG CAAATTCCCG ACGAGGTCGA AACGCATCGA CGTCATATCA AGAATCACTT TCCCGCTGGT GTTTGCTTTG TTCAATCTGG TGTACTGGTC GACCTATTTG TTCAGGGACG AGGCGGAGGA GAATTAG, ( SEQ ID NO : 3 ) . 22. An expression vector for expressing a recombinant C. felis GluClu channel protein wherein said expression vector comprises a DNA molecule of claim 21. 23. A host cell which expresses a recombinant C. felis GluClu channel protein wherein said host cell contains the expression vector of claim 22. 24. A process for expressing a recombinant C. felis GluClu channel protein in a recombinant host cell, comprising: (a) transfecting the expression vector of claim 22 into a suitable host cell; and, (b) culturing the host cells of step (a) under conditions which allow expression of said recombinant C. felis GluClu channel protein from said expression vector. 25. A C felis GluClu channel protein free from otherC. felis proteins which comprises the amino acid sequence set forth in SEQ ID NO:2. 26. A C felis GluClu channel protein of claim 25 which is a product of a DNA expression vector contained within a recombinant host cell. 27. A membrane preparation purified from a recombinant host cell of claim 26. 28. A truncatedC felis GluClu channel protein free from otherC. felis proteins which comprises the amino add sequence set forth in SEQ ID NO:4. 29. A truncatedC. felis GluClu channel protein of claim 28 which is a product of a DNA expression vector contained within a recombinant host cell. 30. A membrane preparation purified from a recombinant host cell of claim 29. 31. A method of identifying a compound that modulates glutamate-gated channel protein activity, which comprises: a) injecting into a host cell solution a population of nucleic acid molecules, at least of portion of which encode a glutamate- gated channel protein, such that expression of said portion of nucleic acid molecules results in an active glutamate-gated channel; b) adding a test compound into said solution; c) measuring host cell membrane current at a holding potential more positive than the reversal potential for chloride. 32. The method of Claim 31 wherein said glutamate gated channel protein is selected from the group consisting of Caenorhabditis elegans, Drosophila melonogaster and Ctenocephalides felis glutamate-gated channel proteins. 33. The method of claim 32 wherein said nucleic acid molecule is selected from the group consisting of complementary DNA, poly A + messenger RNA and complementary RNA. 34. The method of claim 32 wherein said holding potential is 0 mV.

Inventors: BROCHU RICHARD, COHEN CHARLES J, CULLY DORIS F, ETTER ADRIAN, PARESS PHILIP S, WARMKE JEFFREY W, BROCHU, RICHARD, COHEN, CHARLES, J., CULLY, DORIS, F., ETTER, ADRIAN, PARESS, PHILIP, S., WARMKE, JEFFREY, W.
Applicants: BROCHU RICHARD, COHEN CHARLES J, CULLY DORIS F, ETTER ADRIAN, MERCK & CO INC, PARESS PHILIP S, WARMKE JEFFREY W, BROCHU, RICHARD, COHEN, CHARLES, J., CULLY, DORIS, F., ETTER, ADRIAN, MERCK & CO., INC., PARESS, PHILIP, S., WARMKE, JEFFREY, W.
Application year: 1998
Main classification: C12N1
IPC codes: C07K14, C12N1, C12N5, C12N15, C12P21, C12Q1