bluuebunny/crossref_metadata_2025 huggingface dataset:
Intracellular Localization and Trafficking of Serine Proteinase AhSub and Cysteine Proteinase AhCP of
Acanthamoeba healyi
Authors: Moon E.-K. , Lee S.-T. , Chung D.-I. , Kong H.-H.
Published: January 2006

Proteinases have been proposed to play important roles in pathogenesis and various biologic actions in
Acanthamoeba
. Although genetic characteristics of several proteases of
Acanthamoeba
have been reported, the intracellular localization and trafficking of these enzymes has yet to be studied. In the present study, we analyzed the intracellular localization and trafficking of two proteinases, AhSub and AhCP, of
Acanthamoeba healyi
by transient transfection. Full-length AhSub-enhanced green fluorescent protein (EGFP) fusion protein was found in intracellular vesicle-like structures of transfected amoebae. Time-lapse photographs confirmed the secretion of the fluorescent material of the vesicle toward the extracellular space. The mutated AhSub, of which the pre or prepro region was deleted, was found to localize diffusely throughout the cytoplasm of the amoeba rather than concentrated in the secretory vesicle. Transfection of the construct containing the pre region only showed the same localization and trafficking of the full-length AhSub. A cysteine proteinase AhCP-EGFP fusion protein showed similar localization in the vesicle-like structure in the amoeba. However, using Lyso Tracker analysis, these vesicular structures of AhCP were confirmed to be lysosomes rather than secretory vesicles. The AhCP construct with a deletion of the prepro region showed a dispersed distribution of fluorescence in the cytoplasm of the cells. These results indicated that AhSub and AhCP would play different roles in
Acanthameoba
biology and that the pre region of AhSub and pro region of AhCP are important for proper intracellular localization and trafficking of each proteinase.
Deletion of
RTS1
, Encoding a Regulatory Subunit of Protein Phosphatase 2A, Results in Constitutive Amino Acid Signaling via Increased Stp1p Processing
Authors: Eckert-Boulet Nadine , Larsson Katrin , Wu Boqian , Poulsen Peter , Regenberg Birgitte , Nielsen Jens , Kielland-Brandt Morten C.
Published: January 2006

In
Saccharomyces cerevisiae
, extracellular amino acids are sensed at the plasma membrane by the SPS sensor, consisting of the transporter homologue Ssy1p, Ptr3p, and the endoprotease Ssy5p. Amino acid sensing results in proteolytic truncation of the transcription factors Stp1p and Stp2p, followed by their relocation from the cytoplasm to the nucleus, where they activate transcription of amino acid permease genes. We screened a transposon mutant library for constitutively signaling mutants, with the aim of identifying down-regulating components of the SPS-mediated pathway. Three isolated mutants were carrying a transposon in the
RTS1
gene, which encodes a regulatory subunit of protein phosphatase 2A. We investigated the basal activity of the
AGP1
and
BAP2
promoters in
rts1Δ
cells and found increased transcription from these promoters, as well as increased Stp1p processing, even in the absence of amino acids. Based on our findings we propose that the phosphatase complex containing Rts1p keeps the SPS-mediated pathway down-regulated in the absence of extracellular amino acids by dephosphorylating a component of the pathway.
Developmentally Regulated DNA Methylation in
Dictyostelium discoideum
Authors: Katoh Mariko , Curk Tomaz , Xu Qikai , Zupan Blaz , Kuspa Adam , Shaulsky Gad
Published: January 2006

Methylation of cytosine residues in DNA plays a critical role in the silencing of gene expression, organization of chromatin structure, and cellular differentiation of eukaryotes. Previous studies failed to detect 5-methylcytosine in
Dictyostelium
genomic DNA, but the recent sequencing of the
Dictyostelium
genome revealed a candidate DNA methyltransferase gene (
dnmA
). The genome sequence also uncovered an unusual distribution of potential methylation sites, CpG islands, throughout the genome. DnmA belongs to the Dnmt2 subfamily and contains all the catalytic motifs necessary for cytosine methyltransferases. Dnmt2 activity is typically weak in
Drosophila melanogaster
, mouse, and human cells and the gene function in these systems is unknown. We have investigated the methylation status of
Dictyostelium
genomic DNA with antibodies raised against 5-methylcytosine and detected low levels of the modified nucleotide. We also found that DNA methylation increased during development. We searched the genome for potential methylation sites and found them in retrotransposable elements and in several other genes. Using Southern blot analysis with methylation-sensitive and -insensitive restriction endonucleases, we found that the DIRS retrotransposon and the
guaB
gene were indeed methylated. We then mutated the
dnmA
gene and found that DNA methylation was reduced to about 50% of the wild-type level. The mutant cells exhibited morphological defects in late development, indicating that DNA methylation has a regulatory role in
Dictyostelium
development. Our findings establish a role for a Dnmt2 methyltransferase in eukaryotic development.
Heterologous Expression of an
Entamoeba histolytica
Chitin Synthase in
Saccharomyces cerevisiae
Authors: Van Dellen Katrina L. , Bulik Dorota A. , Specht Charles A. , Robbins Phillips W. , Samuelson John C.
Published: January 2006

Chitin in the cyst wall of
Entamoeba histolytica
is made by two chitin synthases (Chs), one of which is unique (EhCHS-1) and one of which resembles those of insects and nematodes (EhCHS-2). EhCHS-1 is deposited chitin in the lateral wall of transformed
Saccharomyces cerevisiae
Chs mutants, independent of accessory proteins (Chs4p to Chs7p) required by yeast Chs3p.
The
akuB
KU80
Mutant Deficient for Nonhomologous End Joining Is a Powerful Tool for Analyzing Pathogenicity in
Aspergillus fumigatus
Authors: da Silva Ferreira Márcia Eliana , Kress Marcia R. V. Z. , Savoldi Marcela , Goldman Maria Helena S. , Härtl Albert , Heinekamp Thorsten , Brakhage Axel A. , Goldman Gustavo H.
Published: January 2006

To increase the frequency of homologous recombination, we inactivated the
KU80
homologue in
Aspergillus fumigatus
(named
akuB
KU80
). Homologous integration reached about 80% for both calcineurin A (
calA
) and polyketide synthase
pksP (alb1
) genes in the
akuB
KU80
mutant to 3 and 5%, respectively, when using a wild-type
A. fumigatus
strain. Deletion of
akuB
KU80
had no influence on pathogenicity in a low-dose murine infection model.
Gene Targeting in
Aspergillus fumigatus
by Homologous Recombination Is Facilitated in a Nonhomologous End- Joining-Deficient Genetic Background
Authors: Krappmann Sven , Sasse Christoph , Braus Gerhard H.
Published: January 2006

The
akuA
gene encoding the Ku70 component of the nonhomologous end-joining machinery was deleted in the opportunistic pathogen
Aspergillus fumigatus
. No obvious phenotype could be assessed for the corresponding mutant strain but relative frequencies of homologous recombination were increased as deduced from targeting the laccase-encoding
abr2
gene.
Genome-Based Approaches to Understanding Phosphorus Deprivation Responses and PSR1 Control inChlamydomonas reinhardtii
Authors: Moseley Jeffrey L. , Chang Chiung-Wen , Grossman Arthur R.
Published: January 2006

TheChlamydomonas reinhardtiitranscription factor PSR1 is required for the control of activities involved in scavenging phosphate from the environment during periods of phosphorus limitation. Increased scavenging activity reflects the development of high-affinity phosphate transport and the expression of extracellular phosphatases that can cleave phosphate from organic compounds in the environment. A comparison of gene expression patterns using microarray analyses and quantitative PCRs with wild-type andpsr1mutant cells deprived of phosphorus has revealed that PSR1 also controls genes encoding proteins with potential “electron valve” functions—these proteins can serve as alternative electron acceptors that help prevent photodamage caused by overexcitation of the photosynthetic electron transport system. In accordance with this finding, phosphorus-starvedpsr1mutants die when subjected to elevated light intensities; at these intensities, the wild-type cells still exhibit rapid growth. Acclimation to phosphorus deprivation also involves a reduction in the levels of transcripts encoding proteins involved in photosynthesis and both cytoplasmic and chloroplast translation as well as an increase in the levels of transcripts encoding stress-associated chaperones and proteases. Surprisingly, phosphorus-deficientpsr1cells (but not wild-type cells) also display expression patterns associated with specific responses to sulfur deprivation, suggesting a hitherto unsuspected link between the signal transduction pathways involved in controlling phosphorus and sulfur starvation responses. Together, these results demonstrate that PSR1 is critical for the survival of cells under conditions of suboptimal phosphorus availability and that it plays a key role in controlling both scavenging responses and the ability of the cell to manage excess absorbed excitation energy.
Pair of Unusual GCN5 Histone Acetyltransferases and ADA2 Homologues in the Protozoan ParasiteToxoplasma gondii
Authors: Bhatti Micah M. , Livingston Meredith , Mullapudi Nandita , Sullivan William J.
Published: January 2006

GCN5 is a histone acetyltransferase (HAT) essential for development in mammals and critical to stress responses in yeast. The protozoan parasiteToxoplasma gondiiis a serious opportunistic pathogen. The study of epigenetics and gene expression in this ancient eukaryote has pharmacological relevance and may facilitate the understanding of these processes in higher eukaryotes. Here we show that the disruption ofT. gondiiGCN5 yields viable parasites, which were subsequently employed in a proteomics study to identify gene products affected by its loss. Promoter analysis of these TgGCN5-dependent genes, which were mostly parasite specific, reveals a conserved T-rich element. The loss of TgGCN5 does not attenuate virulence in an in vivo mouse model. We also discovered thatT. gondiiis the only invertebrate reported to date possessing a second GCN5 (TgGCN5-B). TgGCN5-B harbors a strikingly divergent N-terminal domain required for nuclear localization. Despite high homology between the HAT domains, the two TgGCN5s exhibit differing substrate specificities. In contrast to TgGCN5-A, which exclusively targets lysine 18 of H3, TgGCN5-B acetylates multiple lysines in the H3 tail. We also identify two ADA2 homologues that interact differently with the TgGCN5s. TgGCN5-B has the potential to compensate for TgGCN5-A, which probably arose from a gene duplication unique toT. gondii. Our work reveals an unexpected complexity in the GCN5 machinery of this primitive eukaryote.
Dissociation of Cytokinesis Initiation from Mitotic Control in a Eukaryote
Authors: Kumar Praveen , Wang C. C.
Published: January 2006

Cytokinesis is initiated only after mitotic exit in eukaryotes. However, in the insect (procyclic) form of an ancient protist,
Trypanosoma brucei
, a blockade at the G
2
/M checkpoint results in an enrichment of anucleate cells (zoids), suggesting separated regulations between mitosis and cytokinesis (X. Tu and C. C. Wang, J. Biol. Chem.
279:
20519-20528, 2004). Polo-like kinases (Plks) are known to play critical roles in controlling both mitosis and cytokinesis. A single
Plk
homologue in
T. brucei
, Tb
PLK
, was found to be capable of complementing the Plk (Cdc5) functions in
Saccharomyces cerevisiae
, thus raising the question of how it may function in the trypanosome with cytokinesis dissociated from mitosis. Depletion of TbPLK in the procyclic form of
T. brucei
by RNA interference resulted in growth arrest with accumulation of multiple nuclei, kinetoplasts, basal bodies, and flagella in approximately equal numbers among individual cells. There were, however, few zoids detectable, indicating inhibited cytokinesis with unblocked mitosis and kinetoplast segregation. TbPLK is thus apparently involved only in initiating cytokinesis in
T. brucei
. Overexpression of TbPLK in the trypanosome did not affect cell growth, but 13% of the resulting population was in the zoid form, suggesting runaway cytokinesis. An immunofluorescence assay indicated that TbPLK was localized in a chain of likely flagellum attachment zones in the cytoskeleton. In a dividing cell, a new line of such zones appeared closely paralleling the existing one, which could constitute the cleavage furrow. An exposed region of TbPLK at the anterior tip of the cell may provide the trigger of cytokinesis. Taken together, our results revealed a novel mechanism of cytokinesis initiation in the trypanosome that may serve as a useful model for further in-depth investigations.
MOLECULAR MECHANISM OF 7TM RECEPTOR ACTIVATION—A GLOBAL TOGGLE SWITCH MODEL
Authors: Schwartz Thue W. , Frimurer Thomas M. , Holst Birgitte , Rosenkilde Mette M. , Elling Christian E.
Published: January 2006

▪ Abstract  The multitude of chemically highly different agonists for 7TM receptors apparently do not share a common binding mode or active site but nevertheless act through induction of a common molecular activation mechanism. A global toggle switch model is proposed for this activation mechanism to reconcile the accumulated biophysical data supporting an outward rigid-body movement of the intracellular segments, as well as the recent data derived from activating metal ion sites and tethered ligands, which suggests an opposite, inward movement of the extracellular segments of the transmembrane helices. According to this model, a vertical see-saw movement of TM-VI—and to some degree TM-VII—around a pivot corresponding to the highly conserved prolines will occur during receptor activation, which may involve the outer segment of TM-V in an as yet unclear fashion. Small-molecule agonists can stabilize such a proposed active conformation, where the extracellular segments of TM-VI and -VII are bent inward toward TM-III, by acting as molecular glue deep in the main ligand-binding pocket between the helices, whereas larger agonists, peptides, and proteins can stabilize a similar active conformation by acting as Velcro at the extracellular ends of the helices and the connecting loops.
REGULATION OF PHOSPHOLIPASE C ISOZYMES BY RAS SUPERFAMILY GTPASES
Authors: Harden T. Kendall , Sondek John
Published: January 2006

▪ Abstract  The physiological effects of many extracellular stimuli are mediated by receptor-promoted activation of phospholipase C (PLC) and consequential activation of inositol lipid-signaling pathways. These signaling responses include the classically described conversion of PtdIns(4,5)P2 to the Ca2+-mobilizing second messenger Ins(1,4,5)P3 and the protein kinase C–activating second messenger diacylglycerol as well as alterations in membrane association or activity of many proteins that harbor phosphoinositide binding domains. Here we discuss how the family of PLCs elaborates a minimal catalytic core typified by PLC-δ to confer multiple modes of regulation on their phospholipase activities. Although PLC-dependent signaling is prominently regulated by direct interactions with heterotrimeric G proteins or tyrosine kinases, the existence of at least 13 divergent PLC isozymes promises a diverse repertoire of regulatory mechanisms for this class of important signaling proteins. We focus here on the recently realized and extensive regulation of inositol lipid signaling by Ras superfamily GTPases directly acting on PLC isozymes and conclude by considering the biological and pharmacological ramifications of this regulation.
Voltage-gated potassium channel Kv1.3 regulates GLUT4 trafficking to the plasma membrane via a Ca2+-dependent mechanism
Authors: Li Yanyan , Wang Peili , Xu Jianchao , Desir Gary V.
Published: January 2006

Kv1.3 is a voltage-gated K+ channel expressed in insulin-sensitive tissues. We previously showed that gene inactivation or pharmacological inhibition of Kv1.3 channel activity increased peripheral insulin sensitivity independently of body weight by augmenting the amount of GLUT4 at the plasma membrane. In the present study, we further examined the effect Kv1.3 on GLUT4 trafficking and tested whether it occurred via an insulin-dependent pathway. We found that Kv1.3 inhibition by margatoxin (MgTX) stimulated glucose uptake in adipose tissue and skeletal muscle and that the effect of MgTX on glucose transport was additive to that of insulin. Furthermore, whereas the increase in uptake was wortmannin insensitive, it was completely inhibited by dantrolene, a blocker of Ca2+ release from intracellular Ca2+ stores. In white adipocytes in primary culture, channel inhibition by Psora-4 increased GLUT4 translocation to the plasma membrane. In these cells, GLUT4 protein translocation was unaffected by the addition of wortmannin but was significantly inhibited by dantrolene. Channel inhibition depolarized the membrane voltage and led to sustained, dantrolene-sensitive oscillations in intracellular Ca2+ concentration. These results indicate that the apparent increase in insulin sensitivity observed in association with inhibition of Kv1.3 channel activity is mediated by an increase in GLUT4 protein at the plasma membrane, which occurs largely through a Ca2+-dependent process.
Green tea extract and its major polyphenol (−)-epigallocatechin gallate improve muscle function in a mouse model for Duchenne muscular dystrophy
Authors: Dorchies Olivier M. , Wagner Stéphanie , Vuadens Ophélie , Waldhauser Katri , Buetler Timo M. , Kucera Pavel , Ruegg Urs T.
Published: January 2006

Duchenne muscular dystrophy is a frequent muscular disorder caused by mutations in the gene encoding dystrophin, a cytoskeletal protein that contributes to the stabilization of muscle fiber membrane during muscle activity. Affected individuals show progressive muscle wasting that generally causes death by age 30. In this study, the dystrophic mdx 5Cv mouse model was used to investigate the effects of green tea extract, its major component (−)-epigallocatechin gallate, and pentoxifylline on dystrophic muscle quality and function. Three-week-old mdx 5Cv mice were fed for either 1 or 5 wk a control chow or a chow containing the test substances. Histological examination showed a delay in necrosis of the extensor digitorum longus muscle in treated mice. Mechanical properties of triceps suræ muscles were recorded while the mice were under deep anesthesia. Phasic and tetanic tensions of treated mice were increased, reaching values close to those of normal mice. The phasic-to-tetanic tension ratio was corrected. Finally, muscles from treated mice exhibited 30–50% more residual force in a fatigue assay. These results demonstrate that diet supplementation of dystrophic mdx 5Cv mice with green tea extract or (−)-epigallocatechin gallate protected muscle against the first massive wave of necrosis and stimulated muscle adaptation toward a stronger and more resistant phenotype.
Effect of differing antecedent hypoglycemia on counterregulatory responses to exercise in type 1 diabetes
Authors: Galassetti Pietro , Tate Donna , Neill Ray A. , Richardson Antoinette , Leu Szu-Yun , Davis Stephen N.
Published: January 2006

Hypoglycemia frequently occurs during or after exercise in intensively treated patients with type 1 diabetes mellitus (T1DM), but the underlying mechanisms are not clear. In both diabetic and nondiabetic subjects, moderate hypoglycemia blunts counterregulatory responses to subsequent exercise, but it is unknown whether milder levels of hypoglycemia can exert similar effects in a dose-dependent fashion. This study was designed to test the hypothesis that prior hypoglycemia of differing depths induces acute counterregulatory failure of proportionally greater magnitude during subsequent exercise in T1DM. Twenty-two T1DM patients (11 males/11 females, HbA1c8.0 ± 0.3%) were studied during 90 min of euglycemic cycling exercise after two 2-h periods of previous day euglycemia or hypoglycemia of 3.9, 3.3, or 2.8 mmol/l (HYPO-3.9, HYPO-3.3, HYPO-2.8, respectively). Patients' counterregulatory responses (circulating levels of neuroendocrine hormones, intermediary metabolites, substrate flux, tracer-determined glucose kinetics, and cardiovascular measurements) were assessed during exercise. Identical euglycemia and basal insulin levels were successfully maintained during all exercise studies, regardless of blood glucose levels during the previous day. After day 1 euglycemia, patients displayed normal counterregulatory responses to exercise. Conversely, when identical exercise was performed after day 1 hypoglycemia of increasing depth, a progressively greater blunting of glucagon, catecholamine, cortisol, endogenous glucose production, and lipolytic responses to exercise was observed. This was paralleled by a graduated increase in the amount of exogenous glucose needed to maintain euglycemia during exercise. Our results demonstrate that acute counterregulatory failure during prolonged, moderate-intensity exercise may be induced in a dose-dependent fashion by differing depths of antecedent hypoglycemia starting at only 3.9 mmol/l in patients with T1DM.
Hyperoxia decreases muscle glycogenolysis, lactate production, and lactate efflux during steady-state exercise
Authors: Stellingwerff Trent , LeBlanc Paul J. , Hollidge Melanie G. , Heigenhauser George J. F. , Spriet Lawrence L.
Published: January 2006

The aim of this study was to determine whether the decreased muscle and blood lactate during exercise with hyperoxia (60% inspired O2) vs. room air is due to decreased muscle glycogenolysis, leading to decreased pyruvate and lactate production and efflux. We measured pyruvate oxidation via PDH, muscle pyruvate and lactate accumulation, and lactate and pyruvate efflux to estimate total pyruvate and lactate production during exercise. We hypothesized that 60% O2would decrease muscle glycogenolysis, resulting in decreased pyruvate and lactate contents, leading to decreased muscle pyruvate and lactate release with no change in PDH activity. Seven active male subjects cycled for 40 min at 70% V̇o2 peakon two occasions when breathing 21 or 60% O2. Arterial and femoral venous blood samples and blood flow measurements were obtained throughout exercise, and muscle biopsies were taken at rest and after 10, 20, and 40 min of exercise. Hyperoxia had no effect on leg O2delivery, O2uptake, or RQ during exercise. Muscle glycogenolysis was reduced by 16% with hyperoxia (267 ± 19 vs. 317 ± 21 mmol/kg dry wt), translating into a significant, 15% reduction in total pyruvate production over the 40-min exercise period. Decreased pyruvate production during hyperoxia had no effect on PDH activity (pyruvate oxidation) but significantly decreased lactate accumulation (60%: 22.6 ± 6.4 vs. 21%: 31.3 ± 8.7 mmol/kg dry wt), lactate efflux, and total lactate production over 40 min of cycling. Decreased glycogenolysis in hyperoxia was related to an ∼44% lower epinephrine concentration and an attenuated accumulation of potent phosphorylase activators ADPfand AMPfduring exercise. Greater phosphorylation potential during hyperoxia was related to a significantly diminished rate of PCr utilization. The tighter metabolic match between pyruvate production and oxidation resulted in a decrease in total lactate production and efflux over 40 min of exercise during hyperoxia.
Sp1/Sp3 binding is associated with cell-specific expression of the glucose-dependent insulinotropic polypeptide receptor gene
Authors: Boylan Michael O. , Jepeal Lisa I. , Wolfe M. Michael
Published: January 2006

The physiological effects of glucose-dependent insulinotropic polypeptide (GIP) are mediated through specific receptors expressed on target cells. Because aberrant GIP receptor ( GIPR) expression has been implicated in abnormal GIP responses associated with type 2 diabetes mellitus and food-induced Cushing's syndrome, we sought to identify factors that regulate the GIPR. We previously demonstrated that sequences between −1 and −100 of the GIPR gene were sufficient to direct transcription in a rat insulinoma cell line (RIN38). In the present study, we compared the 5′-flanking regions of the rat and human GIPR gene and demonstrated 88% identity within the first 92 bp. Subsequent serial deletion analyses showed that the region between −85 and −40 is essential for maximal promoter activity. Within this region, we identified three putative Sp1 binding motifs, located at positions −77, −60, and −50, that can specifically bind both Sp1 and Sp3. Whereas mutation of the Sp1 sites at −50 and −60 led to 36 and 40% reduction in promoter activity, respectively, mutation of the Sp1 motif at −70 did not affect promoter activity. Cotransfection of S2 Schneider cells with GIPR-luciferase chimeric constructs and either Sp1 or Sp3 expression vectors indicated that both Sp1 and the long form of Sp3 activate transcription through binding to the Sp1 sites located between −100 and −40. Lastly, chromatin immunoprecipitation analyses revealed that both Sp1 and Sp3 bind to the GIPR promoter region in RIN38 cells. These results indicate that cell-specific expression of GIPR is associated with the binding of the transcription factors Sp1 and Sp3 to the GIPR promoter.
Role of calcineurin in exercise-induced mitochondrial biogenesis
Authors: Garcia-Roves Pablo M. , Huss Janice , Holloszy John O.
Published: January 2006

Raising cytosolic Ca2+induces an increase in mitochondrial biogenesis in myotubes. This phenomenon mimics the adaptive responses of skeletal muscle to exercise. It has been hypothesized that increases in cytosolic Ca2+during motor nerve activity stimulate mitochondrial biogenesis by activating calcineurin. Overexpression of constitutively active calcineurin increases expression of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and induction of genes involved in mitochondrial energy metabolism in muscle cells. The purpose of this study was to determine whether calcineurin plays a role in the stimulation of mitochondrial biogenesis by exercise. Rats were exercised on 5 successive days by means of swimming. Inhibition of calcineurin with cyclosporin did not prevent the exercise-induced increases in PGC-1α and a range of mitochondrial proteins. In contrast to the other mitochondrial proteins, the increases in cytochrome oxidase (COX)-I and -IV proteins were blocked by cyclosporin treatment. This inhibitory effect of cyclosporin occurred at the posttranscriptional level, as evidenced by normal increases in COX-I and COX-IV mRNAs in response to exercise in the cyclosporin-treated rats. This toxic effect of cyclosporin may account for the decrease in muscle respiratory capacity reported to occur with cyclosporin treatment. In conclusion, inhibition of calcineurin does not prevent the exercise-induced increase in mitochondrial biogenesis in skeletal muscles, providing evidence that the adaptive response is not mediated by activation of calcineurin.
Transient receptor potential vanilloid 1, calcitonin gene-related peptide, and substance P mediate nociception in acute pancreatitis
Authors: Wick Elizabeth C. , Hoge Steven G. , Grahn Sarah W. , Kim Edward , Divino Lorna A. , Grady Eileen F. , Bunnett Nigel W. , Kirkwood Kimberly S.
Published: January 2006

The mechanism of pancreatitis-induced pain is unknown. In other tissues, inflammation activates transient receptor potential vanilloid 1 (TRPV1) on sensory nerves to liberate CGRP and substance P (SP) in peripheral tissues and the dorsal horn to cause neurogenic inflammation and pain, respectively. We evaluated the contribution of TRPV1, CGRP, and SP to pancreatic pain in rats. TRPV1, CGRP, and SP were coexpressed in nerve fibers of the pancreas. Injection of the TRPV1 agonist capsaicin into the pancreatic duct induced endocytosis of the neurokinin 1 receptor in spinal neurons in the dorsal horn (T10), indicative of SP release upon stimulation of pancreatic sensory nerves. Induction of necrotizing pancreatitis by treatment with l-arginine caused a 12-fold increase in the number of spinal neurons expressing the proto-oncogene c-fos in laminae I and II of L1, suggesting activation of nociceptive pathways. l-Arginine also caused a threefold increase in spontaneous abdominal contractions detected by electromyography, suggestive of referred pain. Systemic administration of the TRPV1 antagonist capsazepine inhibited c-fos expression by 2.5-fold and abdominal contractions by 4-fold. Intrathecal, but not systemic, administration of antagonists of CGRP (CGRP8–37) and SP (SR140333) receptors attenuated c-fos expression in spinal neurons by twofold. Thus necrotizing pancreatitis activates TRPV1 on pancreatic sensory nerves to release SP and CGRP in the dorsal horn, resulting in nociception. Antagonism of TRPV1, SP, and CGRP receptors may suppress pancreatitis pain.
Parietal cell hyperstimulation and autoimmune gastritis in cholera toxin transgenic mice
Authors: Lopez-Diaz Lymari , Hinkle Karen L. , Jain Renu N. , Zavros Yana , Brunkan Cynthia S. , Keeley Theresa , Eaton Kathryn A. , Merchant Juanita L. , Chew Catherine S. , Samuelson Linda C.
Published: January 2006

The stimulation of gastric acid secretion from parietal cells involves both intracellular calcium and cAMP signaling. To understand the effect of increased cAMP on parietal cell function, we engineered transgenic mice expressing cholera toxin (Ctox), an irreversible stimulator of adenylate cyclase. The parietal cell-specific H+,K+-ATPase β-subunit promoter was used to drive expression of the cholera toxin A1 subunit (CtoxA1). Transgenic lines were established and tested for Ctox expression, acid content, plasma gastrin, tissue morphology, and cellular composition of the gastric mucosa. Four lines were generated, with Ctox-7 expressing ∼50-fold higher Ctox than the other lines. Enhanced cAMP signaling in parietal cells was confirmed by observation of hyperphosphorylation of the protein kinase A-regulated proteins LASP-1 and CREB. Basal acid content was elevated and circulating gastrin was reduced in Ctox transgenic lines. Analysis of gastric morphology revealed a progressive cellular transformation in Ctox-7. Expanded patches of mucous neck cells were observed as early as 3 mo of age, and by 15 mo, extensive mucous cell metaplasia was observed in parallel with almost complete loss of parietal and chief cells. Detection of anti-parietal cell antibodies, inflammatory cell infiltrates, and increased expression of the Th1 cytokine IFN-γ in Ctox-7 mice suggested that autoimmune destruction of the tissue caused atrophic gastritis. Thus constitutively high parietal cell cAMP results in high acid secretion and a compensatory reduction in circulating gastrin. High Ctox in parietal cells can also induce progressive changes in the cellular architecture of the gastric glands, corresponding to the development of anti-parietal cell antibodies and autoimmune gastritis.
Inhibition of active lymph pump by simulated microgravity in rats
Authors: Gashev Anatoliy A. , Delp Michael D. , Zawieja David C.
Published: January 2006

During spaceflight the normal head-to-foot hydrostatic pressure gradients are eliminated and body fluids shift toward the head, resulting in a diminished fluid volume in the legs and an increased fluid volume in the head, neck, and upper extremities. Lymphatic function is important in the maintenance of normal tissue fluid volume, but it is not clear how microgravity influences lymphatic pumping. We performed a detailed evaluation of the influence of simulated microgravity on lymphatic diameter, wall thickness, elastance, tone, and other measures of phasic contractility in isolated lymphatics. Head-down tail suspension (HDT) rats were used to simulate the effects of microgravity. Animals were exposed to HDT for 2 wk, after which data were collected and compared with the control non-HDT group. Lymphatics from four regional lymphatic beds (thoracic duct, cervical, mesenteric, and femoral lymphatics) were isolated, cannulated, and pressurized. Input and output pressures were adjusted to apply a range of transmural pressures and flows to the lymphatics. Simulated microgravity caused a potent inhibition of pressure/stretch-stimulated pumping in all four groups of lymphatics. The greatest inhibition was found in cervical lymphatics. These findings presumably are correlated to the cephalic fluid shifts that occur in HDT rats as well as those observed during spaceflight. Flow-dependent pump inhibition was increased after HDT, especially in the thoracic duct. Mesenteric lymphatics were less strongly influenced by HDT, which may support the idea that lymph hydrodynamic conditions in the mesenteric lymphatic during HDT are not dramatically altered.
Effect of decreased O2supply on skeletal muscle oxygenation and O2consumption during sepsis: role of heterogeneous capillary spacing and blood flow
Authors: Goldman Daniel , Bateman Ryon M. , Ellis Christopher G.
Published: January 2006

One of the main aspects of the initial phase of the septic inflammatory response to a bacterial infection is abnormal microvascular perfusion, including decreased functional capillary density (FCD) and increased blood flow heterogeneity. On the other hand, one of the most important phenomena observed in the later stages of sepsis is an increased dependence of tissue O2utilization on the convective O2supply. This “pathological supply dependency” is associated with organ failure and poor clinical outcomes. Here, a detailed theoretical model of capillary-to-tissue O2transport during sepsis is used to examine the origins of abnormal supply dependency. With use of three-dimensional arrays of capillaries with heterogeneous spacing and blood flow, steady-state O2transport is simulated numerically during reductions in the O2supply. Increased supply dependency is shown to occur in sepsis for hypoxic (decreased hemoglobin O2saturation) and stagnant (decreased blood flow) hypoxia. For stagnant hypoxia, a reduction in FCD with decreasing blood flow is necessary to obtain the observed increase in supply dependency. Our results imply that supply dependency observed under normal conditions does not have its origin at the level of individual capillaries. In sepsis, however, diffusion limitation and shunting of O2by individual capillaries occur to a degree that is dependent on the heterogeneity of septic injury and the arrangement of capillary networks. Thus heterogeneous stoppage of individual capillaries is a likely factor in pathological supply dependency.
Angiotensin-(1–7) prevents development of severe hypertension and end-organ damage in spontaneously hypertensive rats treated with l-NAME
Authors: Benter Ibrahim F. , Yousif Mariam H. M. , Anim J. T. , Cojocel C. , Diz D. I.
Published: January 2006

We examined the influence of chronic treatment with ANG-(1–7) on development of hypertension and end-organ damage in spontaneously hypertensive rats (SHR) chronically treated with the nitric oxide synthesis inhibitor l-NAME (SHR-l-NAME). l-NAME administered orally (80 mg/l) for 4 wk significantly elevated mean arterial pressure (MAP) compared with SHR controls drinking regular water (269 ± 10 vs. 196 ± 6 mmHg). ANG-(1–7) (24 μg·kg−1·h−1) or captopril (300 mg/l) significantly attenuated the elevation in MAP due to l-NAME (213 ± 7 and 228 ± 8 mmHg, respectively), and ANG-(1–7) + captopril completely reversed the l-NAME-dependent increase in MAP (193 ± 5 mmHg). l-NAME-induced increases in urinary protein were significantly lower in ANG-(1–7)-treated animals (226 ± 6 vs. 145 ± 12 mg/day). Captopril was more effective (96 ± 12 mg/day), and there was no additional effect of captopril + ANG-(1–7) (87 ± 5 mg/day). The abnormal vascular responsiveness to endothelin-1, carbachol, and sodium nitroprusside in perfused mesenteric vascular bed of SHR-l-NAME was improved by ANG-(1–7) or captopril, with no additive effect of ANG-(1–7) + captopril. In isolated perfused hearts, recovery of left ventricular function from 40 min of global ischemia was significantly better in ANG-(1–7)- or captopril-treated SHR-l-NAME, with additive effects of combined treatment. The beneficial effects of ANG-(1–7) on MAP and cardiac function were inhibited when indomethacin was administered with ANG-(1–7), but indomethacin did not reverse the protective effects on proteinuria or vascular reactivity. The protective effects of the ANG-(1–7) analog AVE-0991 were qualitatively comparable to those of ANG-(1–7) but were not improved over those of captopril alone. Thus, during reduced nitric oxide availability, ANG-(1–7) attenuates development of severe hypertension and end-organ damage; prostaglandins participate in the MAP-lowering and cardioprotective effects of ANG-(1–7); and additive effects of captopril + ANG-(1–7) on MAP, but not proteinuria or endothelial function, suggest common, as well as different, mechanisms of action for the two treatments. Together, the results provide further evidence of a role for ANG-(1–7) in protective effects of angiotensin-converting enzyme inhibition and suggest dissociation of factors influencing MAP and those influencing end-organ damage.
Reactive oxygen species mediate modification of glycocalyx during ischemia-reperfusion injury
Authors: Rubio-Gayosso Ivan , Platts Steven H. , Duling Brian R.
Published: January 2006

The glycocalyx (Gcx) is a complex and poorly understood structure covering the luminal surface of endothelial cells. It is known to be a determinant of vascular rheology and permeability and may be a key control site for the vascular injuries caused by ischemia-reperfusion (I/R). We used intravital-microscopy to evaluate the effects of I/R injury on two properties of Gcx in mouse cremasteric microvessels: exclusion of macromolecules (anionic-dextrans) and intracapillary distribution of red blood cells (RBC). In this model, the Gcx is rapidly modified by I/R injury with an increase in 70-kDa anionic-dextran penetration without measurable effect on the penetration of 580-kDa anionic-dextran or on RBC exclusion. The effects of I/R injury appear to be mediated by the rapid production of reactive oxygen species (ROS) because they are ameliorated by the addition of exogenous superoxide dismutase-catalase. Intravenous application of allopurinol or heparin also inhibited the effects of I/R injury, and we interpret efficacy of allopurinol as evidence for a role for xanthine-oxidoreductase (XOR) in the response to I/R injury. Heparin, which is hypothesized to displace XOR from a heparin-binding domain in the Gcx, reduced the effects of I/R. The effects of I/R injury were also partially prevented or fully reversed by the intravascular infusion of exogenous hyaluronan. These data demonstrate: 1) the liability of Gcx during I/R injury; 2) the importance of locally produced ROS in the injury to Gcx; and 3) the potential importance of heparin-binding sites in modulating the ROS production. Our findings further highlight the relations between glycosaminoglycans and the pathophysiology of Gcx in vivo.
Excitatory projections from arcuate nucleus to ventrolateral periaqueductal gray in electroacupuncture inhibition of cardiovascular reflexes
Authors: Li Peng , Tjen-A-Looi Stephanie C. , Longhurst John C.
Published: January 2006

We have shown that the modulatory effect of electroacupuncture (EA) on the blood pressure (BP) response induced by visceral organ stimulation is related to inhibition of cardiovascular neurons in the rostral ventrolateral medulla (rVLM) through a mechanism that involves opioids. This effect is long lasting and may involve a long-loop neural supraspinal pathway, including the arcuate nucleus (ARC), which is an important site of opioid neurotransmitter synthesis. Therefore, we evaluated the role of the hypothalamic ARC and its interaction with the midbrain ventrolateral periaqueductal gray (vlPAG) in the EA-BP response. The gallbladder of α-chloralose-anesthetized cats was stimulated to test for the influence of EA on splanchnic afferent-induced cardiovascular reflexes. Electrodes were placed around the splanchnic nerve (SN), and acupuncture needles were applied at P5-6 acupoints overlying the median nerve (MN). Electrophysiological recordings showed that spontaneous activity of ARC and vlPAG neurons was low (1.3 ± 0.5 and 2.0 ± 0.5 spikes/s, respectively). We observed a gradation of responses of ARC neurons to the stimulation of different acupoints, ranging from uniform responses of all neurons during stimulation of the P5-6, LI4-11, H5-6, and St2-G2 located over deep nerves to fewer responses during stimulation of LI6-7 and G37-39 located over superficial nerves. Microinjection of the excitatory amino acid dl-homocysteic acid (DLH 4 nM, 50 nl) into the ARC augmented the responses of vlPAG neurons, whereas microinjection of kainic acid (KA 1 mM, 50 nl) to deactivate neurons in the ARC decreased vlPAG responses to SN stimulation. Thirty minutes of EA at P5-6 increased the SN-evoked discharge of vlPAG neurons (7.0 ± 1.2 to 14.3 ± 3.0 spikes/30 stimuli), a response that was blocked by microinjection of KA into the ARC. Microinjection of DLH into the ARC, like EA, inhibited (30 min) the reflex increase in BP induced by application of bradykinin (BK) to the gallbladder, whereas microinjection of KA into the ARC blocked the inhibitory influence of EA at P5-6 on the BK-induced BP response. These results suggest that excitatory projections from the ARC to the vlPAG are essential to the EA inhibition of the reflex increase in BP induced by SN or gallbladder visceral afferent stimulation.
Longitudinal but not circumferential deformation reflects global contractile function in the right ventricle with open pericardium
Authors: Leather H. Alex , Ama' Ruggero , Missant Carlo , Rex Steffen , Rademakers Frank E. , Wouters Patrick F.
Published: January 2006

The clinical evaluation of right ventricular (RV) contractility is problematic because instantaneous RV volumetry is difficult to achieve. Our aim was to test whether global RV contractility can be assessed by using regional indexes in the longitudinal and/or circumferential axis. Six anesthetized adult ewes were instrumented with a RV conductance catheter and four RV free wall sonomicrometry crystals (interrogating the longitudinal and circumferential axes). Global and regional preload recruitable stroke work (PRSW) were measured by using acute vena cava occlusions at baseline, during esmolol and dobutamine infusion, and during stable low-preload and high-afterload conditions. The agreement between regional and global PRSW was assessed with regression and Bland-Altman analysis. Both regional PRSW indexes correlated well with global PRSW in baseline conditions, during inotropic modulation ( R2 = 0.83 and 0.74 for longitudinal and circumferential regional PRSW, respectively), and during preload reduction ( R2 = 0.62 and 0.83, respectively), but only longitudinal regional PRSW correlated with global PRSW in increased afterload conditions ( R2 = 0.59 and 0.13 for longitudinal and circumferential regional PRSW, respectively). We conclude that in the open-chest, open-pericardium animal model, deformation in the longitudinal axis accurately reflects global RV contractile function in baseline conditions and during acute load modulation, whereas circumferential motion is influenced by changes in afterload.
Blood pressure regulation by ETA and ETB receptors in conscious, telemetry-instrumented mice and role of ETA in hypertension produced by selective ETB blockade
Authors: Fryer Ryan M. , Rakestraw Pamela A. , Banfor Patricia N. , Cox Bryan F. , Opgenorth Terry J. , Reinhart Glenn A.
Published: January 2006

The net contribution of endothelin type A (ETA) and type B (ETB) receptors in blood pressure regulation in humans and experimental animals, including the conscious mouse, remains undefined. Thus we assessed the role of ETA and ETB receptors in the control of basal blood pressure and also the role of ETA receptors in maintaining the hypertensive effects of systemic ETB blockade in telemetry-instrumented mice. Mean arterial pressure (MAP) and heart rate were recorded continuously from the carotid artery and daily (24 h) values determined. At baseline, MAP ranged from 99 ± 1 to 101 ± 1 mmHg and heart rate ranged between 547 ± 15 and 567 ± 19 beats/min ( n = 6). Daily oral administration of the ETB selective antagonist A-192621 [10 mg/kg twice daily] increased MAP to 108 ± 1 and 112 ± 2 mmHg on days 1 and 5, respectively. Subsequent coadministration of the ETA selective antagonist atrasentan (5 mg/kg twice daily) in conjunction with A-192621 (10 mg/kg twice daily) decreased MAP to baseline values on day 6 (99 ± 2 mmHg) and to below baseline on day 8 (89 ± 3 mmHg). In a separate group of mice ( n = 6) in which the treatment was reversed, systemic blockade of ETB receptors produced no hypertension in animals pretreated with atrasentan, underscoring the importance of ETA receptors to maintain the hypertension produced by ETB blockade. In a third group of mice ( n = 10), ETA blockade alone (atrasentan; 5 mg/kg twice daily) produced an immediate and sustained decrease in MAP to values below baseline (baseline values = 101 ± 2 to 103 ± 2 mmHg; atrasentan decreased pressure to 95 ± 2 mmHg). Thus these data suggest that ETA and ETB receptors play a physiologically relevant role in the regulation of basal blood pressure in normal, conscious mice. Furthermore, systemic ETB receptor blockade produces sustained hypertension in conscious telemetry-instrumented mice that is absent in mice pretreated with an ETA antagonist, suggesting that ETA receptors maintain the hypertension produced by ETB blockade.
Cyclooxygenase blockade attenuates responses of group III and IV muscle afferents to dynamic exercise in cats
Authors: Hayes Shawn G. , Kindig Angela E. , Kaufman Marc P.
Published: January 2006

Cyclooxygenase products accumulate in statically contracting muscles to stimulate group III and IV afferents. The role played by these products in stimulating thin fiber muscle afferents during dynamic exercise is unknown. Therefore, in decerebrated cats, we recorded the responses of 17 group III and 12 group IV triceps surae muscle afferents to dynamic exercise, evoked by stimulation of the mesencephalic locomotor region. Each afferent was tested while the muscles were freely perfused and while the circulation to the muscles was occluded. The increases in group III and IV afferent activity during dynamic exercise while the circulation to the muscles was occluded were greater than those during exercise while the muscles were freely perfused ( P < 0.01). Indomethacin (5 mg/kg iv), a cyclooxygenase blocker, reduced the responses to dynamic exercise of the group III afferents by 42% when the circulation to the triceps surae muscles was occluded ( P < 0.001) and by 29% when the circulation was not occluded ( P = 0.004). Likewise, indomethacin reduced the responses to dynamic exercise of group IV afferents by 34% when the circulation was occluded ( P < 0.001) and by 18% when the circulation was not occluded ( P = 0.026). Before indomethacin, the activity of the group IV, but not group III, afferents was significantly higher during postexercise circulatory occlusion than during rest ( P < 0.05). After indomethacin, however, group IV activity during postexercise circulatory occlusion was not significantly different from group IV activity during rest. Our data suggest that cyclooxygenase products play a role both in sensitizing group III and IV afferents during exercise and in stimulating group IV afferents during postexercise circulatory occlusion.