bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic Induction Tomography: A Measuring System for Biological Tissues
Authors: GRIFFITHS H. , STEWART W. R. , GOUGH W.
Published: February 2006

Abstract: A single‐channel magnetic induction system operating at 10 MHz has been constructed. The system consists of an excitation coil and a sensing coil, between which different objects can be scanned. The eddy currents induced in the object cause perturbations in the sensed magnetic field, which are measured with a phase‐sensitive detector with backing off of the signal to improve sensitivity. Scans were obtained for saline solutions with conductivities ranging from 0.001 to 6 Sm−1, encompassing the range for biological tissues. The imaginary part of the perturbation in the sensed magnetic field was found to be proportional to saline conductivity, consistent with theoretical prediction, and had a constant of proportionality of −1.2% per Sm−1. A filtered back‐projection algorithm was used to generate tomographic images from the scans.
Magnetic Impedance Tomographya
Authors: TOZER J. C. , IRELAND R. H. , BARBER D. C. , BARKER A. T.
Published: February 2006

Abstract: Tissue can be characterized by its electrical impedance, especially if measurement can be extended over a range of frequencies. Recently, there has been a great deal of interest in imaging the distribution of electrical impedance through the technique of electrical impedance tomography (EIT). However, EIT has a number of practical problems relating to the placement of electrodes on the body. Such contacts are not required to collect magnetic field data around an object through which current is flowing and thus this approach may be more practical than EIT in the clinical environment. This paper describes the technique of magnetic impedance tomography (MIT), which allows reconstruction of the current distribution from magnetic field measurements. The reconstruction techniques used to generate the images and the prototype data collection system are described. Images produced using data collected from discrete and distributed current phantoms and the thorax during human respiration are presented.
Focused Impedance Measurement (FIM): A New Technique with Improved Zone Localization
Authors: RABBANI K. S. , SARKER M. , AKOND M. H. R. , AKTER T.
Published: February 2006

Abstract:Conventional four‐electrode impedance measurements (FEIM) cannot localize a zone of interest in a volume conductor. On the other hand, the recently developed electrical impedance tomography (EIT) system offers an image with reasonable resolution, but is complex and needs many electrodes. By placing two FEIM systems perpendicular to each other over a common zone at the center and combining the two results, it is possible to obtain enhanced sensitivity over this central zone. This is the basis of the proposed new method of focused impedance measurement (FIM). Sensitivity maps in both 2D and 3D show the desired improvement. A comparison of stomach‐emptying studies also indicates the improvement achieved. This new method may be useful for impedance measurements of large organs like stomach, heart, and lungs. Being much simpler in comparison to EIT, multifrequency systems can be simply built for FIM. Besides, FIM may have utility in other fields like geology where impedance measurements are performed.
State Estimation in Time‐Varying Electrical Impedance Tomography
Authors: KAIPIO JARI P. , KARJALAINEN PASI A. , SOMERSALO ERKKI , VAUHKONEN MARKO
Published: February 2006

Abstract: In electrical impedance tomography (EIT), an estimate for the cross‐sectional impedance distribution is obtained from the body by using current and voltage measurements made from the boundary. All well‐known reconstruction algorithms use a full set of independent current patterns for each reconstruction. In some applications, the impedance changes may be so fast that information on the time evolution of the impedance distribution is either lost or severely blurred. We have recently proposed the formulation of EIT as a state estimation problem and the recursive estimation of the state with the aid of the Kalman filter. In this paper, we study the so‐called smoothing extension of the Kalman filter in the estimation of the time‐varying impedance distribution. We will also discuss how to implement prior spatial information on the solution to the state space formalism. The enhanced performance of the proposed approach is verified with the aid of a simulation.
Static Three‐Dimensional Electrical Impedance Tomography
Authors: VAUHKONEN PIVI J. , VAUHKONEN MARKO , SAVOLAINEN TUOMO , KAIPIO JARI P.
Published: February 2006

Abstract:In electrical impedance tomography, an approximation for the internal resistivity distribution is computed based on the knowledge of the voltages and currents on the surface of the body. Usually, it is assumed that the injected currents stay at the two‐dimensional (2D) electrode plane and the reconstruction is based on 2D assumptions. However, the currents spread out in three dimensions (3D) and therefore the structures out of the current injection plane may have significant effect on the reconstructed images. We have studied possibilities of a finite element‐based method to reconstruct static 3D images from real measurements made on a saline‐filled tank. We show that the 3D static images obtained from simple experiments are better than the 2D difference images obtained from the same object. We further show that the static images obtained with 2D calculations are much worse than the images obtained with 3D calculations. We also discuss the effects of the boundary shape error on the reconstructed static 3D images.
Impedance Mammograph 3D Phantom Studies
Authors: WTOREK JERZY , STELTER JAROSLAW , NOWAKOWSKIM ANTONI
Published: February 2006

Abstract: The results obtained using the Technical University of Gdansk Electroimpedance Mammograph (TUGEM) of a 3D phantom study are presented. The TUGEM system is briefly described. The hardware contains the measurement head and DSP‐based identification modules controlled by a PC computer. A specially developed reconstruction algorithm, Regulated Correction Frequency Algebraic Reconstruction Technique (RCFART), is used to obtain 3D images. To visualize results, the Advance Visualization System (AVS) is used. It allows a powerful image processing on a fast workstation or on a high‐performance computer. Results of three types of 3D conductivity perturbations used in the study (aluminum, Plexiglas, and cucumber) are shown. The relative volumes of perturbations less than 2% of the measurement chamber are easily evidenced.
Tumor Suppressor Gene Smad4/DPC4, Its Downstream Target Genes, and Regulation of Cell Cyclea
Authors: CHIAO PAUL J. , HUNT KELLY K. , GRAU ANA M. , ABRAMIAN ARAM , FLEMING JASON , ZHANG WEI , BRESLIN TARA , ABBRUZZESE JAMES L. , EVANS DOUGLAS B.
Published: February 2006

Abstract: The tumor suppressor gene deleted in pancreatic cancer locus 4 (Smad4/DPC4) is inactivated in about 50% of pancreatic adenocarcinomas. The role of DPC4 in the transforming growth factor‐β (TGF‐β) receptor‐mediated signal transduction cascade in human pancreatic, colon, and breast carcinoma cell lines has been investigated by a number of laboratories. The results demonstrate that Smad4/DPC4 protein functions as a key transcription factor required in regulation of TGF‐β inducible gene expression and subsequent growth inhibition. Many transcription regulators that are involved in cell growth, differentiation, and oncogenesis have been identified and cloned. Yet paradoxically, it is much more difficult to identify the important downstream target genes responsible for the biological effects elicited by these transcription factors. Although numerous attempts have been made and different approaches have been used to identify the target genes, only limited success has been achieved. Our data show that p21waf1 is one of the Smad4/DPC4‐regulated downstream target genes and suggest that overexpression of the Smad4/DPC4 gene can bypass TGF‐β receptor activation and reestablish one of the key regulatory controls of cell proliferation. Identification of the Smad‐regulated downstream target genes responsible for diverse biological processes that they control will extend our understanding of the mechanism for cell cycle regulation and cell differentiation.
Molecular Pathology of Invasive Carcinoma
Authors: LONGNECKER DANIEL S.
Published: February 2006

Abstract: Abnormalities of several oncogenes and tumor suppressor genes have been identified in carcinomas of the pancreas during the last decade, and multiple genetic changes have been demonstrated in individual carcinomas. The variety of genetic changes suggests that multiple etiologic factors contribute to carcinogenesis in the pancreas. Several of these changes are characteristically found in specific types of tumors, suggesting that different causes and molecular mechanisms are involved. One example is the loss of heterozygosity at the von Hippel‐Lindau (VHL) gene locus in both wild type and hereditary serous cystadenomas, and another is the virtual absence of K‐ras mutation and p53 abnormalities in acinar cell carcinomas, whereas both are frequently found in ductal adenocarcinomas. Multiple lines of evidence place K‐ras mutation very early and loss of p53 and p16 as late events during ductal cell carcinogenesis. The timing and order of other genetic changes such as loss of the DPC4 tumor suppressor function is less certain.
Hollow‐Spheres: A New Model for Analyses of Differentiation of Pancreatic Duct Epithelial Cells
Authors: LEHNERT LASSE , TROST HARTWIG , SCHMIEGEL WOLFF , RÖDER CHRISTIAN , KALTHOFF HOLGER
Published: February 2006

Abstract: We discovered a unique feature of a subclone of the pancreatic carcinoma cell line A818. A818‐1‐derived hollow‐spheres developed under three‐dimensional growth conditions. Hollow‐spheres consist of a single layer of 50‐200 epithelial cells surrounding an inner lumen. In contrast to A818‐1, the subclone A818‐4 and all other pancreatic tumor cell lines tested (n= 5), formed spheroids as the only three‐dimensional phenotype. A dramatically reduced proliferation rate compared to the corresponding monolayer was observed in hollow‐spheres when bromodeoxyuridine (BrdU) incorporation was measured. This finding was confirmed by immunostaining using the MIB‐1 antibody. Mechanically disrupted hollow‐spheres not only attached but also grew as monolayer with the same doubling time as the founder cells. Hollow‐spheres developed in fetal calf serum (FCS) containing RPMI 1640 medium without additionally added cytokines. A818‐1 hollow‐sphere formation and integrity was influenced by interferon‐γ. Tumor necrosis factor‐α (TNF‐α) led to cell death. Exogenously added hepatocyte growth factor (HGF) showed no effect neither on hollow‐sphere formation nor on the integrity of completely developed hollow‐spheres. Moreover, no changes were observed when cells were treated with a neutralizing antibody for HGF. Interestingly, hollow‐spheres showed intensive immunoreactivity for the HGF‐receptor (c‐met) and its ligand (HGF). Immunostaining for the biliary glycoprotein (BGP), the non‐specific cross‐reacting antigen 95 (NCA95) and β‐catenin revealed a polar organization of hollow‐spheres. Immunhistochemically, hollow‐spheres were negative for the carcinoembryonic antigen (CEA). When hollow‐spheres were embedded into matrigel, duct‐like tubes grew out. Taken together, A818‐1 hollow‐spheres resemble normally differentiated duct‐like structures and will serve as an excellent model to study differentiation of human pancreatic epithelial cells.
Sp1 and Its Likes: Biochemical and Functional Predictions for a Growing Family of Zinc Finger Transcription Factors
Authors: COOK TIFFANY , GEBELEIN BRIAN , URRUTIA RAUL
Published: February 2006

Abstract: The discovery and functional characterization of Sp1 as a GC‐rich binding zinc finger protein provided a useful paradigm for understanding mechanisms mediating transcriptional activation in eukaryotic cells. This early paradigm suggested that promoters carrying GC‐rich sequences are activated by Sp1 through its interaction with proteins from the basal transcriptional machinery to upregulate gene expression. Since the time of this seminal work, studies from several laboratories have led to the discovery of many Sp1‐like transcription factors containing highly homologous DNA binding motifs that bind to similar sequences. Consequently, this knowledge poses many important questions regarding whether these related proteins have similar or antagonistic biochemical and functional properties to Sp1. The goal of this article is to use available database information and recent experimental evidence to describe the current repertoire of Sp1‐like zinc finger transcription factors in mammalian cells. Furthermore, we discuss structural and functional studies that reveal that these proteins may share a role in morphogenetic pathways. Altogether, this information is aimed at better understanding how this growing family of transcription factors work to regulate gene expression and morphogenesis.
Orthotopic Models of Human Pancreatic Cancer
Authors: CAPELLÁ GABRIEL , FARRÉ LOURDES , VILLANUEVA ALBERTO , REYES GERMÁN , GARCÍ CARME , TARAFA GEMMA , LLUÍS FÈLIX
Published: February 2006

Orthotopic transplantation of solid tumor fragments of human tumors in nude mice reproduces their pattern of local growth and distal dissemination. While lymphatic, hepatic or peritoneal dissemination can be reproduced, perineural invasion is absent. Early passages (less than 3) of xenografts show a high degree of stability regarding K‐ras, p53 and p16 gene status. On the other hand, advanced passages of tumors acquire additional alterations in the p15 and Smad4 genes. Mutations in K‐ras, p53, p15 and Smad4 genes can be acquired, in this model system, in the more advanced stages of pancreatic tumor dissemination. Finally, it is also possible to standardize local growth of these tumors as well as its dissemination pattern giving us a preclinical tool to evaluate the anticancer activity of new drugs.
Hereditary Pancreatitis and Pancreatic Carcinoma
Authors: WHITCOMB DAVID C. , APPLEBAUM SUZANNE , MARTIN STEPHEN P.
Published: February 2006

Abstract: Few risk factors for pancreatic cancer have emerged except for chronic pancreatitis. Recently, hereditary pancreatitis was estimated to carry a standardized incidence ratio of 53, a risk about 25 times higher than smoking. A review of the ongoing hereditary pancreatitis study of the Midwest Multi‐center Pancreatic Study Group suggests that the risk of pancreatic cancer is related to long‐standing pancreatitis rather than to the cationic trypsinogen mutations. No recommendations can be made on screening patients with hereditary pancreatitis for pancreatic cancer at this time. However, prospective data, serum, and pancreatic juice should be collected and banked on consenting patients at risk as part of prospective, multicenter trials so that evidence‐based recommendations for hereditary pancreatitis and other types of chronic pancreatitis can be made in the future.
Acinar‐Ductal‐Carcinoma Sequence in Transforming Growth Factor‐α Transgenic Mice
Authors: SCHMID ROLAND M. , KLÖPPEL GÜNTHER , ADLER GUIDO , WAGNER MARTIN
Published: February 2006

Abstract: Transgenic mice overexpressing transforming growth factor‐α (TGF‐α) display an expansion of intrapancreatic fibroblasts and a progressive accumulation of extracellular matrix. This massive fibrosis is associated with an increase in pancreatic size and weight. In parallel, tubular complexes appear that are composed of acinar cells with a decreased height. These acinar cells lose zymogen granules and become transitional cells, which subsequently gain duct cell features. In animals older than one year dysplastic lesions develop, which originate from tubular complexes. Occasionally these dysplastic foci transform to papillary and cystic pancreatic carcinoma. These tumors are positive for the duct‐specific antigen Duct‐1 and carbonic anhydrase activity indicative of ductal differentiation. Tumors overexpress the epidermal growth factor (EGF)‐receptor and p53, but lack K‐ras mutations. These data suggest an acinar‐ductal‐carcinoma sequence in TGF‐α transgenic mice.
Immunological Escape Mechanisms in Pancreatic Carcinoma
Authors: UNGEFROREN HENDRIK , VOSS MARTINA , BERNSTORFF WOLFRAM V. , SCHMID ANDREAS , KREMER BERND , KALTHOFF HOLGER
Published: February 2006

Abstract: Malignancies have developed several strategies to evade immune surveillance. We have investigated pancreatic cancer cell lines and pancreatic cancer surgical specimens to evaluate possibilities of tumor escape in the Fas system, and local immune suppression. Despite Fas expression the majority of cell lines was resistant to Fas‐mediated apoptosis. The Fas‐associated phosphatase‐1 is a strong candidate to confer Fas resistance in pancreatic cancer cells. In addition, all investigated pancreatic cancer cell lines and cancer specimens expressed Fas ligand. Fas ligand was functional in cancer cell lines as shown by coculture assays of pancreatic cancer cell lines with Jurkat cells as targets. Additional local immune suppression was demonstrated by loss of T‐cell receptor/CD3‐zeta chain of pancreatic cancer infiltrating T‐lymphocytes. We conclude that these tumor escape mechanisms may contribute to the poor prognosis of pancreatic cancer but also represent targets for new treatment modalities.
The Novel Trk Receptor Tyrosine Kinase Inhibitor CEP‐701 (KT‐5555) Exhibits Antitumor Efficacy against Human Pancreatic Carcinoma (Panc1) Xenograft Growth and In Vivo Invasiveness
Authors: MIKNYOCZKI SHEILA J. , DIONNE CRAIG A. , KLEIN‐SZANTO ANDRES J.P. , RUGGERI BRUCE A.
Published: February 2006

Abstract: The survival rate for patients with pancreatic ductal adenocarcinoma (PDAC) is among the poorest for all cancers. The factors that contribute to this poor prognosis are lack of effective early detection, high rate of metastases and a generally refractory response to available treatment modalities.

The most commonly used treatment methods‐chemotherapy and radiation therapy‐are mainly used for symptom palliation, with surgery being the only “curative” treatment option. The use of combinations of treatment modalities is the only therapy available to patients with locally advanced disease or that which is surgically unresectable. These options are still not sufficient to increase patient survival time significantly.

The aggressive behavior and poor prognosis of this cancer is associated with an increased expression of many growth factors and their cognate receptors. We have demonstrated previously the aberrant expression of the Trk receptors (Trks A, B, and C) in PDAC specimens and human PDAC‐derived cell lines and a biphasic, dose‐dependent response of specific neurotrophic agents on the in vitro invasiveness of PDAC cells. Based on these data we have evaluated the therapeutic potential of inhibiting neurotrophin‐Trk interactions using a selective Trk tyrosine kinase inhibitor (CEP‐701) on subcutaneous (s.c.) and tracheal xenografts derived from the poorly differentiated PDAC cell line, Panc1.

We demonstrate that CEP‐701 administration at 10 mg/kg s.c. BID for 21 days inhibited tumor growth of the Panc1 s.c. xenografts in a statistically‐significant manner (p <0.01) compared to vehicle controls, in the absence of morbidity and mortality. A T/C value of 25% was observed for CEP‐701‐treated s.c. xenografts. In addition, CEP‐701 administration inhibited tumor cell invasion in the s.c. tracheal xenograft model of in vivo invasiveness. Taken together, these data suggest that further studies are warranted to evaluate CEP‐701 as a potential therapeutic agent in the treatment of PDAC.
The Matrix Metalloproteinases and Their Inhibitors in the Treatment of Pancreatic Cancer
Authors: JONES LUCIE , GHANEH PAULA , HUMPHREYS MICHELLE , NEOPTOLEMOS JOHN P.
Published: February 2006

Abstract: Matrix metalloproteinases (MMPs) are a family of zinc‐containing proteolytic enzymes that break down extracellular matrix proteins (ECM) in physiological and pathological conditions. Disruption in the tight control of MMP metabolism occurs in cancer, resulting in excessive destruction of theECM, neovascularization, tumor spread and metastases. Recent studies have shown that overexpression of MMPs is associated with poor prognosis. Several MMP inhibitors have been developed and preclinical trials have confirmed a reduction in tumor spread and metastases. Marimastat is a broad spectrum inhibitor, and recent published results shows the drug is well tolerated in patients with advanced cancer. Phase II studies which have used marimistat alone or in combination with other cytotoxic agents, have produced encouraging results with improved survival. Phase III trials are now underway for the use of marimastat in advanced pancreatic cancer and as an adjuvant therapy in patients following resection of pancreatic cancer.
Exocrine Pancreatic Function following Pancreatectomy
Authors: GHANEH PAULA , NEOPTOLEMOS JOHN P.
Published: February 2006

Abstract: Pancreatic exocrine insufficiency can follow major pancreatic resection and result in the malabsorption of fat, causing symptoms of steator‐rhea, abdominal pain and weight loss. The extent of malabsorption will depend on the original disease process and the type and extent of surgical resection. The steatorrhea can be severe and difficult to control, and patients may require high doses of pancreatic enzyme supplements. There have been few studies that have looked at the treatment of steatorrhea postpancreatectomy, and very few randomized studies. Results of the latter have demonstrated that after treatment with oral pancreatic supplements over a third of postpancreatectomy patients still have significant levels of steatorrhea. These results show that even using the best available agents the complete elimination of steatorrhea following major pancreatic resection is not possible at the present time. This indicates a need for further effective therapies.
Characterization of a Human Cell Clone Expressing Cytochrome P450 for Safe Use in Human Somatic Cell Therapy
Authors: GÜNZBURG WALTER H. , KARLE PETER , RENZ RENATE , SALMONS BRIAN , RENNER MATTHIAS
Published: February 2006

Abstract: We have previously demonstrated the therapeutic effect and efficacy of implantation of cells genetically modified to express cytochrome P450 2B1 in a nude mouse tumor model. The cells are encapsulated in polymerized cellulose sulphate and injected into preformed tumors. Upon administration of ifosfamide, the P450 enzyme converts the ifosfamide into antitumorigenic toxic metabolites at the site required, thereby significantly reducing tumor burden. Feline kidney epithelial cells were chosen for these studies, because they are easy to culture and can readily be transfected. However, these cells are not suitable for eventual use in human patients, since they are known to express endogenous retroviruses that are able to infect mammalian cells. They thus represent a safety risk. Here we describe the establishment of a human cell line that has been genetically modified to express the same cytochrome P450 construct and their characterization. The usefulness of mitomycin C treatment, both to protect the cells from the toxic metabolites that they produce and to incapacitate these cells from replicating, should they escape from the capsules, has also been investigated.
Diversity of Mammalian Voltage‐Gated Sodium Channels
Authors: GOLDIN ALLAN L.
Published: February 2006

ABSTRACT: A variety of different isoforms of mammalian voltage‐gated sodium channels have been identified. These channels can be classified into three different types. Eight type 1 isoforms have been identified in the CNS, PNS, skeletal muscle, and heart. All of these channels have been expressed in exogenous systems, and all of the genes have been mapped. Three type 2 isoforms have been identified in heart, uterus, and muscle. These channels diverge from the type 1 channels in critical regions, and have not been functionally expressed, so their significance is unknown. A single isoform identified in the PNS may represent a third class of channels, in that it diverges from both type 1 and 2 channels. The type 3 channel has not been functionally expressed.
α1B N‐Type Calcium Channel Isoforms with Distinct Biophysical Properties
Authors: STEA ANTHONY , DUBEL STEFAN J. , SNUTCH TERRY P.
Published: February 2006

ABSTRACT: N‐type calcium channels both generate the initial calcium signal to trigger neurotransmitter release and also interact with synaptic release proteins at many mammalian central nervous system synapses. Two isoforms of the α1B N‐type channel from rat brain (α1B‐I and α1B‐II) were found to differ in four regions: (1) a glutamate (Glu) to glycine (Gly) substitution in domain I S3; (2) a Gly to Glu substitution in the domain I‐II linker; (3) the insertion or deletion of an alanine (Ala) in the domain I‐II linker; and (4) the presence or absence of serine/phenylalanine/methionine/glycine (SFMG) in the linker between domain III S3‐S4. Comparison of the electrophysiological properties of the α1B‐I and α1B‐II N‐type channels shows that they exhibit distinct kinetics as well as altered current‐voltage relations. Utilizing chimeric α1B‐I and α1B‐II cDNAs, we show that: (1) the Glu 177 to Gly substitution in domain I S3 increases the rate of activation by ∼15‐fold; (2) the presence or absence of Ala 415 in the domain I‐II linker alters current‐voltage relations by ∼10 mV but does not affect channel kinetics; (3) the substitution of Gly 387 to Glu in the domain I‐II linker also has no effect on kinetics; and (4) the presence or absence of SFMG (1236–1239) in domain III S3‐S4 did not significantly affect channel current‐voltage relations, kinetics, or steady state inactivation. We conclude that molecularly distinct α1B isoforms are expressed in rat brain and may account for some of the functional diversity of N‐type currents in native cells.
Interactions of Presynaptic Ca2+ Channels and Snare Proteins in Neurotransmitter Release
Authors: CATTERALL WILLIAM A.
Published: February 2006

ABSTRACT: N‐ and P/Q‐type Ca2+ channels are localized in high density in presynaptic nerve terminals and are crucial elements in neuronal excitation‐secretion coupling. In addition to mediating Ca2+ entry to initiate transmitter release, they are thought to interact directly with proteins of the synaptic vesicle docking/fusion machinery. These Ca2+ channels can be purified from brain as a complex with SNARE proteins, which are involved in exocytosis. In addition, N‐type and P/Q‐type Ca2+ channels are colocalized with syntaxin in high‐density clusters in nerve terminals. The synaptic protein interaction (synprint) sites in the intracellular loop II‐III (LII‐III) of both α1B and α1A subunits of N‐type and P/Q‐type Ca2+ channels bind to syntaxin, SNAP‐25, and synaptotagmin.Ca2+ has a biphasic effect on the interactions of N‐type Ca2+ channels with SNARE complexes, stimulating optimal binding in the range of 10–30 μM. PKC or CaM KII phosphorylation of the N‐type synprint peptide inhibits interactions with SNARE complexes containing syntaxin and SNAP‐25. Introduction of the synprint peptides into presynaptic superior cervical ganglion neurons reversibly inhibits EPSPs from synchronous transmitter release by 42%. At physiological Ca2+ concentrations, synprint peptides significantly reduce transmitter release in injected frog neuromuscular junctions in cell culture, consistent with detachment of 70% of the docked vesicles from Ca2+ channels as analyzed by a theoretical model. Together, these studies suggest that presynaptic Ca2+ channels not only provide the Ca2+ signal required by the exocytotic mechinery, but also contain structural elements that are integral to vesicle docking, priming, and fusion processes.
Neuronal Voltage‐Activated Calcium Channels: On the Roles of the α1Eand β3 Subunits
Authors: SMITH STEPHEN M. , PIEDRAS‐RENTERÌA ERIKA S. , NAMKUNG YOON , SHIN HEE‐SUP , Tsien RICHARD W.
Published: February 2006

ABSTRACT: Many neurons of the central and peripheral nervous systems display multiple high voltage‐activated (HVA) Ca2+ currents, often classified as L‐, N‐, P‐, Q, and R‐type. The heterogeneous properties of these channels have been attributed to diversity in their pore‐forming α1, subunits, in association with various β subunits. However, there are large gaps in understanding how individual subunits contribute to Ca2+ channel diversity. Here we describe experiments to investigate the roles of α1E and β3 subunits in mammalian neurons. The α1E subunit is the leading candidate to account for the R‐type channel, the least understood of the various types of high voltage‐activated Ca2+ channels. Incubation with α1E antisense oligonucleotide caused a 53% decrease in the peak R‐type current density, while no significant changes in the current expression were seen in sense oligonucleotide‐treated cells. The specificity of the α1E antisense oligonucleotides was supported by the lack of change in the amplitude of P/Q current. These results upheld the hypothesis that members of the E class of α1 subunits support the high voltage‐activated R‐type current in cerebellar granule cells. We studied the role of the Ca2+ channel β3 subunit using a gene targeting strategy. In sympathetic β3−/− neurons, the L‐type current was significantly reduced relative to wild type (wt). In addition, N‐type Ca2+ channels made up a smaller proportion of the total Ca2+ current than in wt due to a lower N‐type current density in a group of neurons with small total currents. Voltage‐dependent activation of P/Q‐type Ca2+ channels was described by two Boltzmann components with different voltage dependence. The absence of the β3 subunit was associated with a shift in the more depolarized component of the activation along the voltage axis toward more negative potentials. The overall conclusion is that deletion of the β3 subunit affects at least three distinct types of HVA Ca2+ channel, but no single type of channel is solely dependent on β3.
Contributions of Kv3 Channels to Neuronal Excitability
Authors: RUDY BERNARDO , CHOW ALAN , LAU DAVID , AMARILLO YIMY , OZAITA ANDER , SAGANICH MICHAEL , MORENO HERMAN , NADAL MARCELA S. , HERNANDEZ‐PINEDA RICARDO , HERNANDEZ‐CRUZ ARTURO , ERISIR ALEV , LEONARD CHRISTOPHER , DE Miera ELEAZAR VEGA‐SAENZ
Published: February 2006

ABSTRACT: Four mammalian Kv3 genes have been identified, each of which generates, by alternative splicing, multiple protein products differing in their C‐terminal sequence. Products of the Kv3.1 and Kv3.2 genes express similar delayed‐rectifier type currents in heterologous expression systems, while Kv3.3 and Kv3.4 proteins express A‐type currents. All Kv3 currents activate relatively fast at voltages more positive than −10 mV, and deactivate very fast. The distribution of Kv3 mRNAs in the rodent CNS was studied by in situ hybridization, and the localization of Kv3.1 and Kv3.2 proteins has been studied by immunohistochemistry. Most Kv3.2 mRNAs (∼90%) are present in thalamic‐relay neurons throughout the dorsal thalamus. The protein is expressed mainly in the axons and terminals of these neurons. Kv3.2 channels are thought to be important for thalamocortical signal transmission. Kv3.1 and Kv3.2 proteins are coexpressed in some neuronal populations such as in fast‐spiking interneurons of the cortex and hippocampus, and neurons in the globus pallidus. Coprecipitation studies suggest that in these cells the two types of protein form heteromeric channels. Kv3 proteins appear to mediate, in native neurons, similar currents to those seen in heterologous expression systems. The activation voltage and fast deactivation rates are believed to allow these channels to help repolarize action potentials fast without affecting the threshold for action potential generation. The fast deactivating current generates a quickly recovering afterhyperpolarization, thus maximizing the rate of recovery of Na+ channel inactivation without contributing to an increase in the duration of the refractory period. These properties are believed to contribute to the ability of neurons to fire at high frequencies and to help regulate the fidelity of synaptic transmission. Experimental evidence has now become available showing that Kv3.1‐Kv3.2 channels play critical roles in the generation of fast‐spiking properties in cortical GABAergic interneurons.
Functional and Molecular Aspects of Voltage‐Gated K+ Channel β Subunits
Authors: PONGS OLAF , LEICHER THORSTEN , BERGER MICHAELA , ROEPER JOCHEN , BÄHRING ROBERT , WRAY DENNIS , GIESE KARL PETER , SILVA ALCINO J. , STORM JOHAN F.
Published: February 2006

ABSTRACT: Voltage‐gated potassium channels (Kv) of the Shaker‐related superfamily are assembled from membrane‐integrated α subunits and auxiliary β subunits. The β subunits may increase Kv channel surface expression and/or confer A‐type behavior to noninactivating Kv channels in heterologous expression systems. The interaction of Kvα and Kvβ subunits depends on the presence or absence of several domains including the amino‐terminal N‐type inactivating and NIP domains and the Kvα and Kvβ binding domains. Loss of function of Kvβ1.1 subunits leads to a reduction of A‐type Kv channel activity in hippocampal and striatal neurons of knock‐out mice. This reduction may be correlated with altered cognition and motor control in the knock‐out mice.
The Eag Family of K+ Channels in Drosophila and Mammals
Authors: GANETZKY BARRY , ROBERTSON GAIL A. , WILSON GISELA F. , TRUDEAU MATTHEW C. , TITUS STEVEN A.
Published: February 2006

ABSTRACT: Mutations of eag, first identified in Drosophila on the basis of their leg‐shaking phenotype, cause repetitive firing and enhanced transmitter release in motor neurons. The encoded EAG polypeptide is related both to voltage‐gated K+ channels and to cyclic nucleotide‐gated cation channels. Homology screens identified a family of eag‐related channel polypeptides, highly conserved from nematodes to humans, comprising three subfamilies: EAG, ELK, and ERG. When expressed in frog oocytes, EAG channels behave as voltage‐dependent, outwardly rectifying K+‐selective channels. Mutations of the human eag‐related gene (HERG) result in a form of cardiac arrhythmia that can lead to ventricular fibrillation and sudden death. Electrophysiological and pharmacological studies have provided evidence that HERG channels specify one component of the delayed rectifier, IKr, that contributes to the repolarization phase of cardiac action potentials. An important role or HERG channels in neuronal excitability is also suggested by the expression of these channels in brain tissue. Moreover, mutations of ERG‐type channels in the Drosophila sei mutant cause temperature‐induced convulsive seizures associated with aberrant bursting activity in the flight motor pathway. The in vivo function of ELK channels has not yet been established, but when these channels are expressed in frog oocytes, they display properties intermediate between those of EAG‐ and ERG‐type channels. Coexpression of the K+‐channel b subunit encoded by Hk with EAG in oocytes dramatically increases current amplitude and also affects the gating and modulation of these currents. Biochemical evidence indicates a direct physical interaction between EAG and HK proteins. Overall, these studies highlight the diverse properties of the eag family of K+ channels, which are likely to subserve diverse functions in vivo.
Small‐Conductance Calcium‐Activated Potassium Channels
Authors: BOND CHRIS T. , MAYLIE JAMES , ADELMAN JOHN P.
Published: February 2006

ABSTRACT: SK channels play a fundamental role in all excitable cells. SK channels are potassium selective and are activated by an increase in the level of intracellular calcium, such as occurs during an action potential. Their activation causes membrane hyperpolarization, which inhibits cell firing and limits the firing frequency of repetetive action potentials. The intracellular calcium increase evoked by action potential firing decays slowly, allowing SK channel activation to generate a long‐lasting hyperpolarization termed the slow afterhyperpolarization (sAHP). This spike‐frequency adaptation protects the cell from the deleterious effects of continuous tetanic activity and is essential for normal neurotransmission. Slow AHPs can be classified into two groups, based on sensitivity to the bee venom toxin apamin. In general, apamin‐sensitive sAHPs activate rapidly following a single action potential and decay with a time constant of approximately 150 ms. In contrast, apamin‐insensitive sAHPs rise slowly and decay with a time constant of approximately 1.5 s. The basis for this kinetic difference is not yet understood. Apamin‐sensitive and apamin‐insensitive SK channels have recently been cloned. This chapter will compare with different classes of sAHPs, discuss the cloned SK channels and how they are gated by calcium ions, describe the molecular basis for their different pharmacologies, and review the possible role of SK channels in several pathological conditions.
Dysfunction of Delayed Rectifier Potassium Channels in an Inherited Cardiac Arrhythmia
Authors: SANGUINETTI MICHAEL C.
Published: February 2006

ABSTRACT: The rapid (lKr) and slow (IKs) delayed rectifier K+ currents are key regulators of cardiac repolarization. HERG encodes the Kr channel, and KVLQT1 and hminK encode subunits that coassemble to form Ks channels. Mutations in any one of these genes cause Romano‐Ward syndrome, an autosomal dominant form of long QT syndrome (LQT). Mutations in KVLQT1 and HERG are the most common cause of LQT. Not all missense mutations of HERG or KVLQT1 have the same effect on K+ channel function. Most mutations result in a dominant‐negative effect, but the severity of the resulting phenotype varies widely, as judged by reduction of current induced by coexpression of wild‐type and mutant subunits in heterologous expression systems. Mutations in hminK (S74L, D76N) reduce IKs by shifting the voltage dependence of activation and accelerating channel deactivation. A recessive form of LQT is caused by mutations in either KVLQT1 or hminK. The functional consequences of mutations in delayed rectifier K+ channel subunits are delayed cardiac repolarization, lengthened QT interval, and an increased risk of torsade de pointes and sudden death.
Recent Excitement in the Ionotropic Glutamate Receptor Field
Authors: ZIFF EDWARD B.
Published: February 2006

ABSTRACT: The synapse is a specialized cellular junction with an elaborate and highly evolved capacity for signal transduction. At excitatory synapses, the neurotransmitter glutamate is released from the presynaptic nerve terminal and stimulates several types of glutamate receptors in the postsynaptic membrane. These include the ionotropic receptors, which are glutamate‐gated cation channels, and the metabotropic receptors, which are G protein‐coupled seven‐transmembrane receptors. The ionotropic glutamate receptors have received special attention because of growing evidence that changes in their synaptic abundance, posttranslational modification, or molecular interactions can provide long‐term changes in synaptic strength. This review summarizes new information about the ionotropic glutamate receptors and relates receptor function to the organization of the postsynaptic membrane and the regulation of electrophysiologic and biochemical signaling at the synapse.
The Arrangement of Glutamate Receptors in Excitatory Synapses
Authors: TAKUMI YUTAKA , MATSUBARA ATSUSHI , RINVIK ERIC , OTTERSEN OLE P.
Published: February 2006

ABSTRACT: Electron microscopic immunogold analyses have revealed a highly differentiated arrangement of glutamate receptors at excitatory synapses in the central nervous system. Studies focused on the hippocampus and cerebellum have shown that the postsynaptic specialization is the preferential site of NMDA and AMPA receptor expression, and that the δ2 receptor is similarly concentrated at this site. In cases of colocalization (AMPA and NMDA, or AMPA and δ2) the two receptor types appear to be intermingled rather than segregated to separate parts of the membrane. The different groups of metabotropic receptor exhibit distinct distributions at the synapse: group I receptors occur in membrane domains lateral to the postsynaptic specialization; group II receptors are expressed in preterminal membranes or extra‐synaptically; whereas group III receptors are found in, or close to, the presynaptic active zone consistent with their roles as autoreceptors. The differentiated distribution of glutamate receptors reflects their functional heterogeneity and explains why some receptors are activated only at high firing frequencies.
GluRδ2 and the Development and Death of Cerebellar Purkinje Neurons in Lurcher Mice
Authors: Heintz Nathaniel , De Jager Philip L.
Published: February 2006

ABSTRACT: Lurcher (Lc) is a spontaneous, semidominant mouse neurological mutation. Heterozygous lurcher mice (Lc/+) display ataxia due to a selective, cell‐autonomous, apoptotic death of 90% of cerebellar Purkinje cells during postnatal development. Homozygous lurcher mice (Lc/Lc) die shortly after birth due to massive loss of mid‐ and hindbrain neurons during late embryogenesis. We identified the mutations responsible for neurodegeneration in two independent Lc alleles as identical G‐to‐A transitions that change a highly conserved alanine to a threonine residue in transmembrane domain III of the mouse d2 glutamate receptor gene (GluRE2). Lc/+ Purkinje cells displayed a very high membrane conductance and a depolarized resting potential, indicating the presence of a large, constitutive inward current. Expression of the mutant Gluδd2Lc protein in Xenopus oocytes confirmed these results, demonstrating that lurcher is an inherited neurodegenerative disorder resulting from a gain‐of‐function mutation in a glutamate receptor gene. Further characterization of GluRδ2 signaling and the activation of apoptotic death in Lc Purkinje cells have begun to yield mechanistic insights into this neurodegenerative disease, and to highlight its relationship to neuronal loss following ischemia.
Nicotinic Modulation of Glutamate and GABA Synaptic Transmission in Hippocampal Neurons
Authors: RADCLIFFE KRISTOFER A. , FISHER JANET L. , GRAY RICHARD , DANI JOHN A.
Published: February 2006

ABSTRACT: Although the hippocampus expresses nicotinic acetylcholine receptors (nAChRs) and receives cholinergic innervation, the functional roles of these receptors are not completely understood. Our results indicated that presynaptic nAChRs mediated a calcium influx that enhanced the release of both glutamate and GABA. Fura‐2 detection of calcium in single mossy fiber presynaptic terminals indicated that nAChRs directly mediated a calcium influx. In hippocampal neurons in primary culture, both spontaneous vesicular release and evoked release of glutamate and GABA were enhanced by nicotine. The nicotinic current displayed rapid desensitization kinetics, and the response to nicotine was inhibited by α‐bungarotoxin and methyllcaconitine, suggesting that nAChRs containing the α7 subunit mediated the effect. Modulation of synaptic activity by presynaptic calcium influx may represent a physiological role of acetylcholine in the brain, as well as a mechanism of action of nicotine.
5‐HT Receptor Knockout Mice: Pharmacological Tools or Models of Psychiatric Disorders
Authors: SCEARCE‐LEVIE K. , CHEN J.‐P. , GARDNER E. , HEN R.
Published: February 2006

ABSTRACT: The molecular diversity of cloned serotonin receptor subtypes in the brain makes it difficult to understand the specific modulatory roles played by different receptors. In order to understand the role of the 5‐HT1B receptor subtype in behavior and neuropsychiatric disorders, we have been studying genetic knockout mice lacking the 5‐HT1B receptor. The 5‐HT1B knockout mice show evidence of increased aggression and impulsivity, behavioral patterns that are also associated with reduced 5‐HT function. They also show reduced or absent locomotor stimulation to some serotoninergic drugs, indicating that the locomotor effects of these drugs require the 5‐HT1B receptor. However, in some cases, data obtained with knockout mice conflicts with the pharmacological data. The 5‐HT1B receptor knockout mice show a phenotype of increased vulnerability to drugs of abuse such as cocaine. However, pharmacological studies suggest that 5‐HT1B stimulation enhances the effects of cocaine, while 5‐HT1B blockade can attenuate some of the effects of cocaine. Compensations that enhance dopamine function appear to be responsible for the drug‐vulnerable phenotype of 5‐HT1B receptor knockout mice. By studying these compensations and changes in neural function, we can learn more about the fundamental mechanisms underlying addiction. The 5‐HT1B knockout mice should be considered a model for the disease state of vulnerability to drugs of abuse, rather than a direct pharmacological model of 5‐HT1B receptor function.
Functional and Molecular Diversity of Purinergic Ion Channel Receptors
Authors: MACKENZIE A. B. , SURPRENANT A. , NORTH A. B.
Published: February 2006

ABSTRACT: P2X receptors are membrane ion channels gated by extracellular adenosine 5′‐triphosphate (ATP); nucleotides also activate a family of seven transmembrane G protein‐coupled receptors (P2Y). P2X receptors are widely expressed on mammalian cells, where they can be broadly differentiated into three groups. The first group is almost equally well activated by ATP and its analog αβmethyleneATP (αβmeATP), whereas a second group is not activated by αβmeATP. A third‐group type of receptor (termed P2Z) is distinguished by the fact that the channel opening is followed by cell permeabilization and lysis if the agonist application is continued for more than a few seconds. Seven cDNAs have been cloned that encode P2X receptor subunits. When expressed individually in heterologous systems, P2X1 and P2X3 subunits form channels activated by ATP or αβmeATP; whereas P2X2, P2X4, and P2X5 form channels activated by ATP but not αβmeATP. P2X6 receptors do not express readily, and P2X7 receptors correspond closely in their properties to P2Z. Further phenotypes can be produced when two subunits are coexpressed, indicating heteromultimerization. This chapter compares the properties of the native P2X receptors with those of the cloned and expressed subunits.
Fluorine incorporation in preamorphized silicon
Authors: Impellizzeri G. , Mirabella S. , Bruno E. , Priolo F. , Napolitani E. , Carnera A.
Published: February 2006

We studied the effect of implanted fluorine on B-doped silicon formed by Si preamorphization, solid phase epitaxy (SPE) regrowth and post-SPE thermal treatments. We showed that the fluorine is an efficient diffusion inhibitor for boron, revealing the crucial importance of F implementation in the future generation devices. In samples doped with B we observed an anomalous F accumulation at the dopant implantation peak. Since the physical mechanisms driving these phenomena are not yet well understood, we investigated the effect of the presence of B and/or As on the F incorporation during the SPE process at 580°C. By using As coimplantation (thus modifying the SPE rate) we demonstrated that the above mentioned increased F incorporation is due to a kinetic effect, related to the SPE rate modification by doping, while a F–B chemical bonding is refused. These data shade new light upon the mechanism responsible for B diffusion reduction by F.