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Cyclase Activity (cyclase + activity)
Kinds of Cyclase Activity Selected AbstractsInvolvement of ,, Subunits of Gq/11 in Muscarinic M1 Receptor Potentiation of Corticotropin-Releasing Hormone-Stimulated Adenylyl Cyclase Activity in Rat Frontal CortexJOURNAL OF NEUROCHEMISTRY, Issue 1 2000Maria C. Olianas Abstract : In the present study, we investigated the involvement of ,, subunits of Gq/11 in the muscarinic M1 receptor-induced potentiation of corticotropin-releasing hormone (CRH)-stimulated adenylyl cyclase activity in membranes of rat frontal cortex. Tissue exposure to either one of two ,, scavengers, the QEHA fragment type II adenylyl cyclase and the GDP-bound form of the , subunit of transducin, inhibited the muscarinic M1 facilitatory effect. Moreover, like acetylcholine (ACh), exogenously added ,, subunits of transducin potentiated the CRH-stimulated adenylyl cyclase activity, and this effect was not additive with that elicited by ACh. Western blot analysis indicated the expression in frontal cortex of both type II and type IV adenylyl cyclases, two isoforms stimulated by ,, subunits in synergism with activated Gs. The M1 receptor-induced enhancement of the adenylyl cyclase response to CRH was counteracted by the Gq/11 antagonist GpAnt-2A but not by GpAnt-2, a preferential Gi/o antagonist. In addition, the muscarinic facilitatory effect was inhibited by membrane preincubation with antiserum directed against the C terminus of the , subunit of Gq/11, whereas the same treatment with antiserum against either Gi1/2 or Go was without effect. These data indicate that in membranes of rat frontal cortex, activation of muscarinic M1 receptors potentiates CRH-stimulated adenylyl cyclase activity through ,, subunits of Gq/11. [source] Regulation of Soluble Guanylyl Cyclase Activity by Oestradiol and Progesterone in the Hypothalamus But Not Hippocampus of Female RatsJOURNAL OF NEUROENDOCRINOLOGY, Issue 6 2007A. Reyna-Neyra Oestradiol and progesterone act in the hypothalamus to coordinate the timing of lordosis and ovulation in female rats in part through regulation of nitric oxide (NO) and cyclic guanosine monophosphate (cyclic GMP) signalling pathways. Soluble guanylyl cyclase is an enzyme that produces cyclic GMP when stimulated by NO and plays a crucial role in the display of lordosis behaviour. We examined the effects of oestradiol and progesterone on the stimulation of cyclic GMP synthesis by NO-dependent and independent activators of soluble guanylyl cyclase in preoptic-hypothalamic and hippocampal slices. Ovariectomised Sprague-Dawley rats were injected with oestradiol (2 µg oestradiol benzoate, s.c.) or vehicle for 2 days. Progesterone (500 µg, s.c.) or vehicle was injected 44 h after the first dose of oestradiol. Rats were killed 48 h after the first oestradiol or vehicle injection, and hypothalamus and hippocampus were obtained. NO-dependent activation of soluble guanylyl cyclase was induced by NO donors, sodium nitroprusside or diethylamine NONOate; NO-independent activation of soluble guanylyl cyclase was induced with 3-(5,-hydroxymethyl-2,-furyl)-1-benzyl indazole and 5,-cyclopropyl-2-[1,2fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridine-3-yl]pyridine-4-ylamine. The NO-dependent activators of soluble guanylyl cyclase produced a concentration-dependent increase in cyclic GMP accumulation and induced significantly greater cyclic GMP accumulation in preoptic-hypothalamic slices from animals treated with oestradiol and progesterone than in slices from rats injected with vehicle, oestradiol or progesterone alone. Hormones did not modify soluble guanylyl cyclase activation by NO-independent stimulators or influence NO content in preoptic-hypothalamic slices. Oestradiol and progesterone did not affect activation of soluble guanylyl cyclase in hippocampal slices by any pharmacological agent, indicating a strong regional selectivity for the hormone effect. Thus, oestradiol and progesterone, administered in vivo, enhance the ability of NO to activate soluble guanylyl cyclase in brain areas modulating female reproductive function without an effect on production of NO itself. [source] Platelet Adenylyl Cyclase Activity as a Trait Marker of Alcohol DependenceALCOHOLISM, Issue 6 2000John A. Menninger Background: There is compelling evidence that genetic factors play a major role in the development of alcohol dependence. Platelet adenylyl cyclase (AC) activity has been proposed as a biochemical marker for differentiating alcohol-dependent and nondependent subjects, but the sensitivity and specificity of this marker have not been ascertained. The objective of this study was to determine the sensitivity and specificity of platelet AC activity in identifying alcohol-dependent subjects and to ascertain the effect of medical/psychiatric variables, drinking and smoking history, and age and body weight on AC activity. Methods: The cross-sectional study was conducted from 1995 to 1998. Participants were 210 Australian White men who were community volunteers and alcohol treatment inpatients in Sydney, Australia. There were 41 nondrinkers, 140 drinkers, and 29 men who were entering alcohol treatment. The main outcome measure was platelet AC activity. Classification variables were plasma ethanol, ,-glutamyltransferase, aspartate aminotransferase, serum carbohydrate-deficient transferrin (CDT), and urinary5-hydroxytryptophol/5-hydroxyindoleacetic acid (5-HTOL/5-HIAA) levels, and World Health Organization/International Society for Biomedical Research on Alcoholism Interview Schedule variables, which included alcohol use and dependence criteria. Results: Among subjects who reported abstinence for at least 4 days, both cesium fluoride (CsF)- and forskolin-stimulated platelet AC activities were significantly lower in those with a lifetime history of alcohol dependence compared with those with no such history (p < 0.005 and p < 0.05, respectively). The sensitivity and specificity of CsF-stimulated AC activity to discriminate individuals with a lifetime history of alcohol dependence were 75% and 79%, respectively. Similar values for sensitivity and specificity for CsF-stimulated AC activity were calculated when discriminating current alcohol dependence in the subjects in our sample. Irrespective of the history of alcohol dependence, persons who had consumed alcohol recently (within the last 3,4 days) showed significantly higher mean basal, CsF-stimulated, and forskolin-stimulated AC activity (p < 0.001), as did those who had elevated 5-HTOL/5-HIAA ratios or CDT levels, indicative of recent (heavy) drinking. The "normalization" of platelet AC activity to baseline levels after an individual stops drinking may be related to the generation of new platelets during the abstinence period. Conduct disorder and antisocial personality disorder were not associated with low AC activity, but low forskolin-stimulated AC activity was associated with major depression. Conclusions: We found that CsF- and forskolin-stimulated platelet AC activity discriminates between subjects with and without alcohol dependence in a population of subjects who had not consumed significant quantities of ethanol recently. Recent alcohol consumption is a confounding variable that can alter the measured levels of AC activity. Forskolin-stimulated platelet AC activity also may be influenced by a history of major depression. [source] Alcohol Stimulates Ciliary Motility of Isolated Airway Axonemes Through a Nitric Oxide, Cyclase, and Cyclic Nucleotide-Dependent Kinase MechanismALCOHOLISM, Issue 4 2009Joseph H. Sisson Background:, Lung mucociliary clearance provides the first line of defense from lung infections and is impaired in individuals who consume heavy amounts of alcohol. Previous studies have demonstrated that this alcohol-induced ciliary dysfunction occurs through impairment of nitric oxide (NO) and cyclic nucleotide-dependent kinase-signaling pathways in lung airway ciliated epithelial cells. Recent studies have established that all key elements of this alcohol-driven signaling pathway co-localize to the apical surface of the ciliated cells with the basal bodies. These findings led us to hypothesize that alcohol activates the cilia stimulation pathway at the organelle level. To test this hypothesis we performed experiments exposing isolated demembranated cilia (isolated axonemes) to alcohol and studied the effect of alcohol-stimulated ciliary motility on the pathways involved with isolated axoneme activation. Methods:, Isolated demembranated cilia were prepared from bovine trachea and activated with adenosine triphosphate. Ciliary beat frequency, NO production, adenylyl and guanylyl cyclase activities, cAMP- and cGMP-dependent kinase activities were measured following exposure to biologically relevant concentrations of alcohol. Results:, Alcohol rapidly stimulated axoneme beating 40% above baseline at very low concentrations of alcohol (1 to 10 mM). This activation was specific to ethanol, required the synthesis of NO, the activation of soluble adenylyl cyclase (sAC), and the activation of both cAMP- and cGMP-dependent kinases (PKA and PKG), all of which were present in the isolated organelle preparation. Conclusions:, Alcohol rapidly and sequentially activates the eNOS,NO,GC,cGMP,PKG and sAC,cAMP, PKA dual signaling pathways in isolated airway axonemes. These findings indicate a direct effect of alcohol on airway cilia organelle function and fully recapitulate the alcohol-driven activation of cilia known to exist in vivo and in intact lung ciliated cells in vitro following brief moderate alcohol exposure. Furthermore, these findings indicate that airway cilia are exquisitely sensitive to the effects of alcohol and substantiate a key role for alcohol in the alterations of mucociliary clearance associated with even low levels of alcohol intake. We speculate that this same axoneme-based alcohol activation pathway is down regulated following long-term high alcohol exposure and that the isolated axoneme preparation provides an excellent model for studying the mechanism of alcohol-mediated cilia dysfunction. [source] Indomethacin decreases particulate guanylyl cyclase activity in rat kidneyCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 4 2004JongUn Lee SUMMARY 1.,Effects of non-steroidal anti-inflammatory drugs on the local atrial natriuretic peptide (ANP) and nitric oxide (NO) systems in the kidney were investigated. 2.,Male Sprague-Dawley rats were treated with indomethacin (5 mg/kg, every 12 h, i.p.) for 2 days. The expression of ANP and natriuretic peptide receptor-A (NPR-A) mRNA was determined in the kidney, as was that of endothelial NO synthase (NOS) proteins. Particulate and soluble guanylyl cyclase activities were determined separately. 3.,Following treatment with indomethacin, urinary sodium excretion decreased significantly. Although the renal expression of ANP was not changed significantly, that of NPR-A decreased significantly. The expression of NOS increased significantly. Particulate guanylyl cyclase activity was decreased, whereas the activity of soluble guanylyl cyclase was increased. The catalytic activity of Na+/K+ -ATPase was increased, with no significant changes in its expression. The expression of the type 3 Na/H exchanger and Na,K,2CL cotransporters increased significantly. 4.,The indomethacin-induced decrease in urinary sodium excretion may be attributed, at least in part, to decreased activity of the local ANP/cGMP system. The increased activity of the NO/cGMP system may be a compensatory response to the diminished activity of the prostaglandin system. [source] Atrial natriuretic peptide-dependent photolabeling of a regulatory ATP-binding site on the natriuretic peptide receptor-AFEBS JOURNAL, Issue 21 2005Simon Joubert The natriuretic peptide receptor-A (NPR-A) is composed of an extracellular ligand-binding domain, a transmembrane-spanning domain, a kinase homology domain (KHD) and a guanylyl cyclase domain. Because the presence of ATP or adenylylimidodiphosphate reduces atrial natriuretic peptide (ANP) binding and is required for maximal guanylyl cyclase activity, a direct interaction of ATP with the receptor KHD domain is plausible. Therefore, we investigated whether ATP interacts directly with a binding site on the receptor by analyzing the binding of a photoaffinity analog of ATP to membranes from human embryonic kidney 293 cells expressing the NPR-A receptor lacking the guanylyl cyclase moiety (,GC). We demonstrate that this receptor (NPR-A-,GC) can be directly labeled by 8-azido-3,-biotinyl-ATP and that labeling is highly increased following ANP treatment. The mutant receptor ,KC, which does not contain the KHD, is not labeled. Photoaffinity labeling of the NPR-A-,GC is reduced by 50% in the presence of 550 µm ATP, and competition curve fitting studies indicate a Hill slope of 2.2, suggestive of cooperative binding. This approach demonstrates directly that the interaction of ANP with its receptor modulates the binding of ATP to the KHD, probably through a conformational change in the KHD. In turn, this conformational change is essential for maximal activity. In addition, the ATP analog, 8-azido-adenylylimidodiphosphate, inhibits guanylyl cyclase activity but increases ANP binding to the extracellular domain. These results suggest that the KHD regulates ANP binding and guanylyl cyclase activity independently. [source] The effect of HAMP domains on class IIIb adenylyl cyclases from Mycobacterium tuberculosisFEBS JOURNAL, Issue 12 2004Jürgen U. Linder The genes Rv1318c, Rv1319c, Rv1320c and Rv3645 of Mycobacterium tuberculosis are predicted to code for four out of 15 adenylyl cyclases in this pathogen. The proteins consist of a membrane anchor, a HAMP region and a class IIIb adenylyl cyclase catalytic domain. Expression and purification of the isolated catalytic domains yielded adenylyl cyclase activity for all four recombinant proteins. Expression of the HAMP region fused to the catalytic domain increased activity in Rv3645 21-fold and slightly reduced activity in Rv1319c by 70%, demonstrating isoform-specific effects of the HAMP domains. Point mutations were generated to remove predicted hydrophobic protein surfaces in the HAMP domains. The mutations further stimulated activity in Rv3645 eight-fold, whereas the effect on Rv1319c was marginal. Thus HAMP domains can act directly as modulators of adenylyl cyclase activity. The modulatory properties of the HAMP domains were confirmed by swapping them between Rv1319c and Rv3645. The data indicate that in the mycobacterial adenylyl cyclases the HAMP domains do not display a uniform regulatory input but instead each form a distinct signaling unit with its adjoining catalytic domain. [source] Genetic data indicate that proteins containing the GGDEF domain possess diguanylate cyclase activityFEMS MICROBIOLOGY LETTERS, Issue 1 2001Nora Ausmees Abstract A conserved domain, called GGDEF (referring to a conserved central sequence pattern), is detected in many procaryotic proteins, often in various combinations with putative sensory-regulatory components. Most sequenced bacterial genomes contain several different GGDEF proteins. The function of this domain has so far not been experimentally shown. Through genetic complementation using genes from three different bacteria encoding proteins with GGDEF domains as the only element in common, we present genetic data indicating (a) that the GGDEF domain is responsible for the diguanylate cyclase activity of these proteins, and (b) that the activity of cellulose synthase in Rhizobium leguminosarum bv. trifolii and Agrobacterium tumefaciens is regulated by cyclic di-GMP as in Acetobacter xylinum. [source] Phosphodiesterase inhibition by naloxone augments the inotropic actions of ,-adrenergic stimulationACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 8 2009W. K. PARK Background: In a shock state, naloxone generates the cardiovascular pressor effect by displacing the endogenous opiate-like peptide ,-endorphin, resulting in restoration of the normal response to catecholamines. In addition to this opioid antagonistic effect, the non-opiate receptor-mediated effect has also been proposed. The aim of this study was to define the mechanism of non-opiate receptor-mediated action of naloxone. Methods: In guinea-pig ventricular tissues, cumulative concentration,response curves for isoproterenol as well as for forskolin and 3-isobutylmethylxanthine (IBMX) were obtained by increasing the concentration stepwise. To assess the effect on the phosphodiesterase (PDE), the effects of naloxone on contractile forces induced by isoproterenol (0.05 ,M) in the presence of IBMX, cilostamide (a PDE III inhibitor), or rolipram (a PDE IV inhibitor) were observed. Naloxone-induced changes in cAMP production by isoproterenol both in the absence and in the presence of IBMX were measured. Naloxone-induced changes in cAMP production by forskolin in the presence of IBMX were also measured. Results: Naloxone (30 ,M) produced a leftward shift of the isoproterenol concentration,response curve (0.01,2 ,M) without changing the maximal response. Forskolin (0.5,10 ,M) produced a concentration-dependent increase in contractile forces. Naloxone increased the maximal inotropic response of forskolin. Naloxone showed no effect on the IBMX concentration,response curve. In the presence of IBMX (200 ,M), naloxone did not alter the contractions evoked by isoproterenol or forskolin. Whereas naloxone increased contractile forces significantly (approximately 25%) more than that of isoproterenol in the presence of rolipram, no alteration of contractile forces in the cilostamide-incubated muscles was observed. Naloxone caused a concentration-related increase of cAMP in the absence of IBMX, but caused no change in its presence. Conclusions: The enhancement of myocardial contractility by naloxone in the presence of stimulation of adenylyl cyclase activity appears to be mediated by inhibition of PDE, specifically PDE III. [source] PTH-dependent adenylyl cyclase activation in SaOS-2 cells: Passage dependent effects on G protein interactionsJOURNAL OF CELLULAR PHYSIOLOGY, Issue 1 2002Hong Gao Parathyroid hormone (PTH) sensitive adenylyl cyclase activity (ACA) in SaOS-2 cells varies as a function of cell passage. In early passage (EP) cells (<,6), ACA in response to PTH and forskolin (FOR) was relatively low and equivalent, whereas in late passage (LP) cells (>,22), PTH exceeded FOR dependent ACA. Potential biochemical mechanisms for this passage dependent change in ACA were considered. In EP, prolonged exposure to pertussis toxin (PT) markedly enhanced ACA activity in response to PTH, Isoproterenol and Gpp(NH)p, whereas ACA in response to FOR was decreased. In contrast, the identical treatment of LP with PT diminished all ACA in response to PTH, Gpp(NH)p, and FOR. The dose dependent effects of PT on subsequent [32P]ADP-ribosylation of its substrates, GTPase activity, as well as FOR-dependent ACA, were equivalent in EP and LP. The relative amounts of G,i and G,s proteins, as determined both by Western blot, PT and cholera toxin (CT) dependent [32P]ADP-ribosylation, were quantitatively similar in EP and LP. Western blot levels of G,s and G,i proteins were not influenced by prior exposure to PT. Both PT and CT dependent [32P]ADP-ribosylation were dose-dependently decreased following exposure to PT. However, the PT-dependent decline in CT-dependent [32P]ADP-ribosylation occurred with enhanced sensitivity in LP. The protein synthesis inhibitor cycloheximide partially reversed the PT associated decrease in FOR dependent ACA in EP. In contrast, cycloheximide completely reversed the PT associated decrease in FOR and as well as PTH dependent ACA in LP. G,s activity, revealed by cyc, reconstitution, was not altered either by cell passage or exposure to PT. The results suggest that the coupling between the components of the complex may be pivotally important in the differential responsiveness of early and late passage SaOS-2 cells to PTH. J. Cell. Physiol. 193: 10,18, 2002. © 2002 Wiley-Liss, Inc. [source] Temporal coupling of cyclic AMP and Ca2+/calmodulin-stimulated adenylyl cyclase to the circadian clock in chick retinal photoreceptor cellsJOURNAL OF NEUROCHEMISTRY, Issue 4 2006Shyam S. Chaurasia Abstract cAMP signaling pathways play crucial roles in photoreceptor cells and other retinal cell types. Previous studies demonstrated a circadian rhythm of cAMP level in chick photoreceptor cell cultures that drives the rhythm of activity of the melatonin synthesizing enzyme arylalkylamine N -acetyltransferase and the rhythm of affinity of the cyclic nucleotide-gated channel for cGMP. Here, we report that the photoreceptor circadian clock generates a rhythm in Ca2+/calmodulin-stimulated adenylyl cyclase activity, which accounts for the temporal changes in the cAMP levels in the photoreceptors. The circadian rhythm of cAMP in photoreceptor cell cultures is abolished by treatment with the l -type Ca2+ channel antagonist nitrendipine, while the Ca2+ channel agonist, Bay K 8644, increased cAMP levels with continued circadian rhythmicity in constant darkness. These results indicate that the circadian rhythm of cAMP is dependent, in part, on Ca2+ influx. Photoreceptor cell cultures exhibit a circadian rhythm in Ca2+/calmodulin-stimulated adenylyl cyclase enzyme activity with high levels at night and low levels during the day, correlating with the temporal changes of cAMP in these cells. Transcripts encoding two of the Ca2+/calmodulin-stimulated adenylyl cyclases, type 1 and type 8 (Adcy1 and Adcy8), displayed significant daily rhythms of mRNA expression under a light,dark cycle, but only the Adcy1 transcript rhythm persisted in constant darkness. Similar rhythms of Adcy1 mRNA level and Ca2+/calmodulin-stimulated adenylyl cyclase activity were observed in retinas of 2-week-old chickens. These results indicate that a circadian clock controls the expression of Adcy1 mRNA and Ca2+/calmodulin-stimulated adenylyl cyclase activity; and calcium influx into these cells gates the circadian rhythm of cAMP, a key component in the regulation of photoreceptor function. [source] Regulation of endogenous human NPFF2 receptor by neuropeptide FF in SK-N-MC neuroblastoma cell lineJOURNAL OF NEUROCHEMISTRY, Issue 2 2006Minna-Liisa Änkö Abstract Neuropeptide FF has many functions both in the CNS and periphery. Two G protein-coupled receptors (NPFF1 and NPFF2 receptors) have been identified for neuropeptide FF. The expression analysis of the peptide and receptors, together with pharmacological and physiological data, imply that NPFF2 receptor would be the primary receptor for neuropeptide FF. Here, we report for the first time a cell line endogenously expressing hNPFF2 receptor. These SK-N-MC neuroblastoma cells also express neuropeptide FF. We used the cells to investigate the hNPFF2 receptor function. The pertussis toxin-sensitive inhibition of adenylate cyclase activity upon receptor activation indicated coupling to Gi/o proteins. Upon agonist exposure, the receptors were internalized and the mitogen-activated protein kinase cascade was activated. Upon neuropeptide FF treatment, the actin cytoskeleton was reorganized in the cells. The expression of hNPFF2 receptor mRNA was up-regulated by neuropeptide FF. Concomitant with the receptor mRNA, the receptor protein expression was increased. The homologous regulation of hNPFF2 receptor correlates with our previous results in vivo showing that during inflammation, the up-regulation of neuropeptide FF mRNA precedes that of NPFF2 receptor. The regulation of hNPFF2 receptor by NPFF could also be important in the periphery where neuropeptide FF has been suggested to function as a hormone. [source] Recombinant human serotonin 5A receptors stably expressed in C6 glioma cells couple to multiple signal transduction pathwaysJOURNAL OF NEUROCHEMISTRY, Issue 2 2003Mami Noda Abstract Human serotonin 5A (5-HT5A) receptors were stably expressed in undifferentiated C6 glioma. In 5-HT5A receptors-expressing cells, accumulation of cAMP by forskolin was inhibited by 5-HT as reported previously. Pertussis toxin-sensitive inhibition of ADP-ribosyl cyclase was also observed, indicating a decrease of cyclic ADP ribose, a potential intracellular second messenger mediating ryanodine-sensitive Ca2+ mobilization. On the other hand, 5-HT-induced outward currents were observed using the patch-clamp technique in whole-cell configuration. The 5-HT-induced outward current was observed in 84% of the patched 5-HT5A receptor-expressing cells and was concentration-dependent. The 5-HT-induced current was inhibited when intracellular K+ was replaced with Cs+ but was not significantly inhibited by typical K+ channel blockers. The 5-HT-induced current was significantly attenuated by 1,2-bis(2-aminophenoxy)ethane- N,N,N,,N,-tetraacetic acid (BAPTA) in the patch pipette. Depleting intracellular Ca2+ stores by application of caffeine or thapsigargin also blocked the 5-HT-induced current. Blocking G protein, the inositol triphosphate (IP3) receptor, or pretreatment with pertussis toxin, all inhibited the 5-HT-induced current. IP3 showed a transient increase after application of 5-HT in 5-HT5A receptor-expressing cells. It was concluded that in addition to the inhibition of cAMP accumulation and ADP-ribosyl cyclase activity, 5-HT5A receptors regulate intracellular Ca2+ mobilization which is probably a result of the IP3-sensitive Ca2+ store. These multiple signal transduction systems may induce complex changes in the serotonergic system in brain function. [source] Adenosine A2a receptor-mediated inhibition of rod opsin mRNA expression in tiger salamanderJOURNAL OF NEUROCHEMISTRY, Issue 3 2002Peter D. Alfinito Abstract The neuromodulator adenosine mediates dark-adaptive changes in retinal photoreceptors through A2a receptors. In cold-blooded vertebrates, opsin mRNA expression is lower at night than during the day. In the present study, we tested whether adenosine could inhibit opsin mRNA expression in cultured rod cells and if endogenous adenosine acts to suppress opsin mRNA in the intact retina at night. Semi-quantitative in situ hybridization showed that treatment with 100 nm of the A2a/A2b agonist N,6 -[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)-ethyl]adenosine (DPMA) reduced opsin mRNA 41% in cultured rod cells. The effect of DPMA was blocked by 10 µm of the A2a antagonist 8-(3-chlorostyryl)caffeine (CSC) but not by 10 µm of the A2b antagonist alloxazine. One micromolar adenosine alone had no effect on opsin mRNA. However, in the presence of the adenosine deaminase inhibitor erythro -9-(2-hydroxy-3-nonyl)adenine hydrochloride (EHNA), 1 µm adenosine reduced opsin mRNA 61%. EHNA alone reduced opsin mRNA by 26%. Consistent with an A2a receptor mechanism, 100 nm forskolin (adenylate cyclase agonist) decreased opsin mRNA 34%. Finally, northern blots showed that intravitreal injection of 10 µm CSC at night increased opsin I mRNA 38%. Thus, endogenous adenosine suppresses rod opsin I mRNA expression at night; in vitro results indicate this reduction occurs through A2a -like receptor binding and stimulation of adenylate cyclase activity. [source] Functional characterization of alternatively spliced 5-HT2 receptor isoforms from the pharynx and muscle of the parasitic nematode, Ascaris suumJOURNAL OF NEUROCHEMISTRY, Issue 2 2002Xinyan Huang Abstract Serotonin (5-HT) receptors play key regulatory roles in nematodes and alternatively spliced 5-HT2 receptor isoforms have been identified in the parasitic nematode, Ascaris suum. 5-HT2As1 and 5-HT2As2 contain different C-termini, and 5-HT2As1,4 lacks 42 amino acids at the C-terminus of the third intracellular loop. 5-HT2As1 and 5-HT2As2 exhibited identical pharmacological profiles when stably expressed in human embryonic kidney (HEK) 293 cells. Both 5-HT2As isoforms had higher affinity for 5-HT than their closely related Caenorhabditis elegans homolog (5-HT2Ce). This increased 5-HT affinity was not related to the substitution in 5-HT2As1 of F120 for Y in the highly conserved DRY motif found in the second intracellular loop of other 5-HT receptors, since a 5-HT2As1F120Y mutant actually exhibited increased 5-HT affinity compared with that of 5-HT2As1. As predicted, cells expressing either 5-HT2As1 or 5-HT2As2 exhibited a 5-HT-dependent increase in phosphatidylinositol (PI) turnover. In contrast, although 5-HT2As1,4 displayed a 10-fold higher affinity for 5-HT and 5-HT agonists than either 5-HT2As1 or 5-HT2As2, 5-HT2As1,4 did not couple to either PI turnover or adenyl cyclase activity. Based on RT,PCR, 5-HT2As1 and 5-HT2As2 were more highly expressed in pharynx and body wall muscle and 5-HT2As1,4 in nerve cord/hypodermis. This is the first report of different alternatively spliced 5-HT2 receptor isoforms from any system. [source] Cyclic ADP-ribose as a potential second messenger for neuronal Ca2+ signalingJOURNAL OF NEUROCHEMISTRY, Issue 2 2001Haruhiro Higashida Cyclic ADP-ribose (cADPR), a known endogenous modulator of ryanodine receptor Ca2+ releasing channels, is found in the nervous system. Injection of cADPR into neuronal cells primarily induces a transient elevation of intracellular Ca2+ concentration ([Ca2+]i), and/or secondarily potentiates [Ca2+]i increases that are the result of depolarization-induced Ca2+ influx. Acetylcholine release from cholinergic neurons is facilitated by cADPR. cADPR modifies K+ currents or elicits Ca2+ -dependent inward currents. cADPR is synthesized by both membrane-bound and cytosolic forms of ADP-ribosyl cyclase in neuronal cells. cADPR hydrolase activity is weak in the membrane fraction, but high in the cytoplasm. Cytosolic ADP-ribosyl cyclase activity is upregulated by nitric oxide/cyclic GMP-dependent phosphorylation. Stimulation of muscarinic and ,-adrenergic receptors activates membrane-bound ADP-ribosyl cyclase via G proteins within membranes of neuronal tumor cells and cortical astrocytes. These findings strongly suggest that cADPR is a second messenger in Ca2+ signaling in the nervous system, although many intriguing issues remain to be addressed before this identity is confirmed. [source] Involvement of ,, Subunits of Gq/11 in Muscarinic M1 Receptor Potentiation of Corticotropin-Releasing Hormone-Stimulated Adenylyl Cyclase Activity in Rat Frontal CortexJOURNAL OF NEUROCHEMISTRY, Issue 1 2000Maria C. Olianas Abstract : In the present study, we investigated the involvement of ,, subunits of Gq/11 in the muscarinic M1 receptor-induced potentiation of corticotropin-releasing hormone (CRH)-stimulated adenylyl cyclase activity in membranes of rat frontal cortex. Tissue exposure to either one of two ,, scavengers, the QEHA fragment type II adenylyl cyclase and the GDP-bound form of the , subunit of transducin, inhibited the muscarinic M1 facilitatory effect. Moreover, like acetylcholine (ACh), exogenously added ,, subunits of transducin potentiated the CRH-stimulated adenylyl cyclase activity, and this effect was not additive with that elicited by ACh. Western blot analysis indicated the expression in frontal cortex of both type II and type IV adenylyl cyclases, two isoforms stimulated by ,, subunits in synergism with activated Gs. The M1 receptor-induced enhancement of the adenylyl cyclase response to CRH was counteracted by the Gq/11 antagonist GpAnt-2A but not by GpAnt-2, a preferential Gi/o antagonist. In addition, the muscarinic facilitatory effect was inhibited by membrane preincubation with antiserum directed against the C terminus of the , subunit of Gq/11, whereas the same treatment with antiserum against either Gi1/2 or Go was without effect. These data indicate that in membranes of rat frontal cortex, activation of muscarinic M1 receptors potentiates CRH-stimulated adenylyl cyclase activity through ,, subunits of Gq/11. [source] Dependence of Hyperpolarisation-Activated Cyclic Nucleotide-Gated Channel Activity on Basal Cyclic Adenosine Monophosphate Production in Spontaneously Firing GH3 CellsJOURNAL OF NEUROENDOCRINOLOGY, Issue 7 2006K. Kretschmannova Abstract The hyperpolarisation-activated cyclic nucleotide-gated (HCN) channels play a distinct role in the control of membrane excitability in spontaneously active cardiac and neuronal cells. Here, we studied the expression and role of HCN channels in pacemaking activity, Ca2+ signalling, and prolactin secretion in GH3 immortalised pituitary cells. Reverse transcriptase-polymerase chain reaction analysis revealed the presence of mRNA transcripts for HCN2, HCN3 and HCN4 subunits in these cells. A hyperpolarisation of the membrane potential below ,,60 mV elicited a slowly activating voltage-dependent inward current (Ih) in the majority of tested cells, with a half-maximal activation voltage of ,89.9 ± 4.2 mV and with a time constant of 1.4 ± 0.2 s at ,120 mV. The bath application of 1 mM Cs+, a commonly used inorganic blocker of Ih, and 100 µM ZD7288, a specific organic blocker of Ih, inhibited Ih by 90 ± 4.1% and 84.3 ± 1.8%, respectively. Receptor- and nonreceptor-mediated activation of adenylyl and soluble guanylyl cyclase and the addition of a membrane permeable cyclic adenosine monophosphate (cAMP) analogue, 8-Br-cAMP, did not affect Ih. Inhibition of basal adenylyl cyclase activity, but not basal soluble guanylyl cyclase activity, led to a reduction in the peak amplitude and a leftward shift in the activation curve of Ih by 23.7 mV. The inhibition of the current was reversed by stimulation of adenylyl cyclase with forskolin and by the addition of 8-Br-cAMP, but not 8-Br-cGMP. Application of Cs+ had no significant effect on the resting membrane potential or electrical activity, whereas ZD7288 exhibited complex and Ih -independent effects on spontaneous electrical activity, Ca2+ signalling, and prolactin release. These results indicate that HCN channels in GH3 cells are under tonic activation by basal level of cAMP and are not critical for spontaneous firing of action potentials. [source] Interaction of ACTH synthetic fragments with rat adrenal cortex membranesJOURNAL OF PEPTIDE SCIENCE, Issue 8 2007Yulia A. Kovalitskaya Abstract Synthetic peptide, corresponding to the amino acid sequence 11,24 of human adrenocorticotropic hormone (ACTH), was labeled with tritium (specific activity of 22 Ci/mmol). [3H]ACTH (11,24) was found to bind to rat adrenal cortex membranes with high affinity and specificity (Kd = 1.8 ± 0.1 nM). Twenty nine fragments of ACTH (11,24) have been synthesized and their ability to inhibit the specific binding of [3H]ACTH (11,24) to adrenocortical membranes has been investigated. Unlabeled fragment ACTH 15,18 (KKRR) was found to replace in a concentration-dependent manner [3H]ACTH (11,24) in the receptor,ligand complex (Ki = 2.3 ± 0.2 nM). ACTH (15,18) was labeled with tritium (specific activity of 20 Ci/mmol). [3H]ACTH (15,18) was found to bind to rat adrenal cortex membranes with high affinity (Kd = 2.1 ± 0.1 nM). The specific binding of [3H]ACTH (15,18) was inhibited by unlabeled ACTH (11,24) (Ki = 2.2 ± 0.1 nM). ACTH (15,18) at the concentration range of 1,1000 nM did not affect the adenylate cyclase activity in adrenocortical membranes. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd. [source] Antioxidants, vitamin C and dithiothreitol, activate membrane-bound guanylate cyclase in PC12 cellsJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 2 2001Zi-Jiang Chen Antioxidants and antioxidant enzymes are known to protect against cell death induced by reactive oxygen species. However, apart from directly quenching free radicals, little is known about the effect of antioxidants on hormone-activated second messenger systems. We previously found that antioxidants such as 17-, estradiol and resveratrol activate membrane-bound guanylate cyclase GC-A, the receptor for atrial natriuretic factor (ANF), in PC12 cells. It is possible that other antioxidants may also activate membrane-bound guanylate cyclase GC-A. The aim of this study was to determine if dithiothreitol (DTT), vitamin C, and vitamin E activate membrane-bound guanylate cyclase GC-A in PC12 cells. The results showed that both DTT and vitamin C increased cGMP levels in PC12 cells, whereas vitamin E had no effect. DTT and vitamin C inhibited membrane-bound guanylate cyclase activity stimulated by ANF in PC12 cells. In contrast, DTT and vitamin C had no effect on soluble guanylate cyclase activity stimulated by substance P. Furthermore, NO synthase inhibitors L-NAME and aminoguanidine did not affect DTT- and vitamin C-stimulated guanylate cyclase activity. The results indicate that DTT and vitamin C, but not vitamin E, activate membrane-bound guanylate cyclase GC-A in PC12 cells. [source] Acutely administered melatonin decreases somatostatin-binding sites and the inhibitory effect of somatostatin on adenylyl cyclase activity in the rat hippocampusJOURNAL OF PINEAL RESEARCH, Issue 2 2004Rosa María Izquierdo-Claros Abstract:, Melatonin is known to increase neuronal activity in the hippocampus, an effect contrary to that of somatostatin (somatotropin release-inhibiting factor, SRIF). Thus, the aim of this study was to investigate whether the somatostatinergic system is implicated in the mechanism of action of melatonin in the rat hippocampus. One group of rats was injected a single dose of melatonin [25 ,g/kg subcutaneously (s.c.)] or saline containing ethanol (0.5%, s.c.) and killed 5 hr later. Melatonin significantly decreased the SRIF-like immunoreactivity levels and induced a significant decrease in the density of SRIF receptors as well as in the dissociation constant (Kd). SRIF-mediated inhibition of basal and forskolin-stimulated adenylyl cyclase activity was markedly decreased in hippocampal membranes from melatonin-treated rats. The functional activity of Gi proteins was similar in hippocampal membranes from melatonin-treated and control rats. Western blot analyses revealed that melatonin administration did not alter Gi,1 or Gi,2 levels. To determine if the changes observed were related to melatonin-induced activation of central melatonin receptors, a melatonin receptor antagonist, luzindole, was administered prior to melatonin injection. Pretreatment with luzindole (10 mg/kg, s.c.) did not alter the melatonin-induced effects on the above-mentioned parameters and luzindole, alone, had no observable effect. The present results demonstrate that melatonin decreases the activity of the SRIF receptor,effector system in the rat hippocampus, an effect which is apparently not mediated by melatonin receptors. As SRIF exerts an opposite effect to that of melatonin on hippocampal neuronal activity, it is possible that the SRIFergic system could be implicated in the mechanism of action of melatonin in the rat. [source] Effects of subchronic and chronic melatonin treatment on somatostatin binding and its effects on adenylyl cyclase activity in the rat frontoparietal cortexJOURNAL OF PINEAL RESEARCH, Issue 4 2002Rosa María Izquierdo-Claros Abstract: Melatonin and somatostatin are known to exert similar effects on locomotor activity. We have previously demonstrated that acute melatonin treatment regulates somatostatin receptor function in the rat frontoparietal cortex. However, the effects of subchronic and chronic melatonin treatment on the somatostatin receptor-G protein,adenylyl cyclase system in the rat frontoparietal cortex are unknown. Melatonin was administered subcutaneously at a daily dose of 25 ,g/kg for 4 days, 1 wk or 2 wk. Twenty-four hours after the last injection, the animals were sacrificed. Melatonin did not alter the somatostatin-like immunoreactivity content in the frontoparietal cortex from control and melatonin-treated rats during any of the previously indicated periods. Four days of melatonin administration induced both an increase in the number of [125I]-Tyr11 -somatostatin receptors and a decrease in the affinity of somatostatin for its receptors in frontoparietal cortical membranes. The increased number of somatostatin receptors in the melatonin-treated rats was associated with an increased capacity of somatostatin to inhibit basal and forskolin-stimulated adenylyl cyclase activity. Melatonin administration for 4 days induced a higher adenylyl cyclase activity both under basal conditions and after direct stimulation of the enzyme with forskolin. No significant differences were observed in the function of Gi proteins in the 4-day melatonin-treated rats. Western blot analyses showed that the 4-day melatonin treatment reduced Gi,2 levels, without altering the amount of Gi,1. These melatonin-induced changes reverted to control values after 7 or 14 days of treatment. Altogether, the present findings suggest that subchronic melatonin treatment modulates the somatostatin receptor/effector system in the rat frontoparietal cortex. [source] Biological Markers of Alcohol Consumption in Nondrinkers, Drinkers, and Alcohol-Dependent Brazilian PatientsALCOHOLISM, Issue 7 2002N. B. Figlie Background The purpose of this study was to compare the sensitivity and specificity of some new and traditional biological markers and indicators of health among Brazilian nondrinkers, drinkers, and alcohol-dependent patients. Material and Methods We evaluated 130 nondrinkers, 167 drinkers, and 183 alcohol-dependent drinkers from Brazil who participated in the WHO/ISBRA Study on State and Trait Markers of Alcohol Use and Dependence. A standardized WHO/ISBRA Interview Schedule provided background information on the subjects' characteristics including reported health problems and alcohol consumption. Blood samples were analyzed for aspartate aminotransferase (AST), carbohydrate deficient transferrin (CDT), ,-glutamyltransferase (GGT), blood alcohol levels (BAL), and platelet adenylate cyclase activity (basal levels [AC] and levels after stimulation with Gpp(NH)p, cesium fluoride, and forskolin). Results The alcohol-dependent drinkers presented higher levels of AST, GGT, AC, CDT, and BAL than the nondrinkers and drinkers, whose levels were similar. Sex differences in the sensitivity of CDT and AC were found. The alcohol-dependent women presented a lower prevalence of abnormal values of CDT and Gpp(NH)p-stimulated AC than the alcohol-dependent men, despite the fact that they presented similar alcohol consumption levels. The alcohol-dependent drinkers presented a higher prevalence of clinical disorders than the nondrinkers and drinkers. The drinkers and alcohol-dependent patients presented significantly higher rates of gastritis than the nondrinkers. Conclusions Sex differences in the sensitivity of CDT and AC suggest that these markers are not as sensitive at detecting excessive alcohol use in women as they are in men. If data from this Brazilian sample are compared with those reported for international samples, relevant differences are detected, which suggests that genetic and cultural differences should be considered in the selection of biological markers of heavy alcohol consumption. [source] The RNA binding protein CsrA controls cyclic di-GMP metabolism by directly regulating the expression of GGDEF proteinsMOLECULAR MICROBIOLOGY, Issue 1 2008Kristina Jonas Summary The carbon storage regulator CsrA is an RNA binding protein that controls carbon metabolism, biofilm formation and motility in various eubacteria. Nevertheless, in Escherichia coli only five target mRNAs have been shown to be directly regulated by CsrA at the post-transcriptional level. Here we identified two new direct targets for CsrA, ycdT and ydeH, both of which encode proteins with GGDEF domains. A csrA mutation caused mRNA levels of ycdT and ydeH to increase more than 10-fold. RNA mobility shift assays confirmed the direct and specific binding of CsrA to the mRNA leaders of ydeH and ycdT. Overexpression of ycdT and ydeH resulted in a more than 20-fold increase in the cellular concentration of the second messenger cyclic di-GMP (c-di-GMP), implying that both proteins possess diguanylate cyclase activity. Phenotypic characterization revealed that both proteins are involved in the regulation of motility in a c-di-GMP-dependent manner. CsrA was also found to regulate the expression of five additional GGDEF/EAL proteins and a csrA mutation led to modestly increased cellular levels of c-di-GMP. All together, these data demonstrate a global role for CsrA in the regulation of c-di-GMP metabolism by regulating the expression of GGDEF proteins at the post-transcriptional level. [source] Analysis of FimX, a phosphodiesterase that governs twitching motility in Pseudomonas aeruginosaMOLECULAR MICROBIOLOGY, Issue 4 2006Barbara I. Kazmierczak Summary Type IV pili (Tfp) are polar surface structures of Pseudomonas aeruginosa required for twitching motility, biofilm formation and adherence. One protein required for the assembly of tfp is FimX, which possesses both GGDEF and EAL domains characteristic of diguanylate cyclases and phosphodiesterases respectively. In this work we demonstrate that FimX has phosphodiesterase activity towards bis-(3,-5,)-cyclic dimeric guanosine monophosphate (c-di-GMP), but does not show diguanylate cyclase activity. Instead, the imperfect GGDEF domain of FimX likely serves to activate phosphodiesterase activity when bound to GTP, as has recently been described for the Caulobacter crescentus composite GGDEF-EAL protein, CC3396. Bacteria expressing FimX in which either the GGDEF or EAL domain is deleted or mutated have phenotypes indistinguishable from a ,fimX strain, demonstrating the importance of both domains to function. Previous work has shown that FimX localizes to the bacterial pole. In this work we show that restriction of FimX to a single pole requires intact GGDEF and EAL domains. Deletion of the amino-terminal REC domain of FimX, which contains a putative polar localization signal, results in a protein that still supports intermediate levels of pilus assembly and function. RFP,FimX,REC, unlike RFP,FimX, is no longer localized to the bacterial pole, while transmission electron microscopy shows that surface pili can originate from non-polar sites in this mutant. Although ,fimX mutants show limited in vitro cytotoxicity, they are as virulent as the wild-type strain in a murine model of acute pneumonia. [source] Halogenated volatile anesthetics inhibit carbon monoxide-stimulated soluble guanylyl cyclase activity in rat brainACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 3 2000E. Masaki Background: Because of halogen contents, halogenated volatile anesthetics (HVA) have a similarity to nitric oxide (NO) in terms of great affinity for the ferrous ion. Interactions between HVA and NO at the ferrous ion of soluble guanylyl cyclase (sGC) have been reported in different tissues. Carbon monoxide (CO), a more stable gas than NO, activates sGC by the same mechanism as NO. This study was undertaken to examine the effect of HVA on CO-stimulated sGC activity in rat brain. Methods: Sprague-Dawley rat brain was homogenized and ultracentrifuged. The resulting supernatant was used as sGC fraction. The fraction was incubated with CO and HVA, and the activity of sGC was determined by measuring cyclic guanosine monophosphate (cGMP) production using an enzyme immunoassay in aliquots of the supernatant. Results: CO clearly increased cGMP production in a dose-dependent manner. Sevoflurane and isoflurane produced significant and dose-dependent inhibition of CO-stimulated sGC activity. There was no difference in the inhibitory effect between the two anesthetics. GTP dose-dependently increased CO-stimulated cGMP production. Both anesthetics decreased GTP production, but the inhibition by the anesthetics was not significant at higher GTP concentrations. Conclusions: These results suggest that HVA can compete with CO at the ferrous ion of sGC and inhibit the activity of this enzyme. [source] Laminin acts via focal adhesion kinase/phosphatidylinositol-3, kinase/protein kinase B to down-regulate ,1 -adrenergic receptor signalling in cat atrial myocytesTHE JOURNAL OF PHYSIOLOGY, Issue 3 2009Y. G. Wang We previously reported that short-term (2 h) plating of cat atrial myocytes on the extracellular matrix protein, laminin (LMN) decreases adenylate cyclase activity and ,1 -adrenergic receptor (,1 -AR) stimulation of L-type Ca2+ current (ICa,L). The present study sought to determine whether LMN-mediated down-regulation of ,1 signalling is due to down-regulation of adenylate cyclase and to gain insight into the signalling mechanisms responsible. ,1 -AR stimulation was achieved by 0.01 ,m isoproterenol (isoprenaline) plus 0.1 ,m ICI 118551, a selective ,2 -AR antagonist. Atrial myocytes were plated for at least 2 h on uncoated cover-slips (,LMN) or cover-slips coated with LMN (+LMN). As previously reported, ,1 -AR stimulation of ICa,L was significantly smaller in +LMN compared to ,LMN atrial myocytes. In ,LMN myocytes, 10 ,m LY294002 (LY), a specific inhibitor of PI-(3)K, had no effect on ,1 -AR stimulation of ICa,L. In +LMN myocytes, however, LY significantly increased ,1 -AR stimulation of ICa,L. Western blots revealed that compared with ,LMN myocytes, +LMN myocytes showed a significant increase in Akt phosphorylation at Ser-473, which was prevented by LY. In another approach, +LMN myocytes were infected (multiplicity of infection (MOI), 100; 24 h) with replication-defective adenoviruses (Adv) expressing dominant-negative inhibitors of focal adhesion kinase (FAK) (Adv-FRNK or Adv-Y397F-FAK) or Akt (Adv-dnAkt). Compared with control cells infected with Adv-,-galactosidase, cells infected with Adv-FRNK, Adv-Y397F-FAK or Adv-dnAkt each exhibited a significantly greater ,1 -AR stimulation of ICa,L. In ,LMN myocytes LY had no effect on forskolin (FSK)-stimulated ICa,L. However, in +LMN myocytes LY significantly increased FSK-stimulated ICa,L. Similar results were obtained in +LMN atrial myocytes infected with Adv-FRNK. We conclude that LMN binding to ,1 -integrin receptors acts via FAK/PI-(3)K/Akt to inhibit adenylate cyclase activity and thereby down-regulates ,1 -AR-mediated stimulation of ICa,L. These findings provide new insight into the cellular mechanisms by which the extracellular matrix can modulate atrial ,-AR signalling. [source] ABA activates ADPR cyclase and cADPR induces a subset of ABA-responsive genes in ArabidopsisTHE PLANT JOURNAL, Issue 3 2004Juan-Pablo Sánchez Summary Cyclic ADP-ribose (cADPR) was previously shown to activate transient expression of two abscisic acid (ABA)-responsive genes in tomato cells. Here, we show that the activity of the enzyme responsible for cADPR synthesis, ADP-ribosyl (ADPR) cyclase, is rapidly induced by ABA in both wild-type (WT) and abi1-1 mutant Arabidopsis plants in the absence of protein synthesis. Furthermore, in transgenic Arabidopsis plants, induced expression of the Aplysia ADPR cyclase gene resulted in an increase in ADPR cyclase activity and cADPR levels, as well as elevated expression of ABA-responsive genes KIN2, RD22, RD29a, and COR47 (although to a lesser extent than after ABA induction). Genome-wide profiling indicated that about 28% of all ABA-responsive genes in Arabidopsis are similarly up- and downregulated by cADPR and contributed to the identification of new ABA-responsive genes. Our results suggest that activation of ADPR cyclase is an early ABA-signaling event partially insensitive to the abi1-1 mutation and that an increase in cADPR plays an important role in downstream molecular and physiological ABA responses. [source] Is cyclic AMP formation desensitized in patients with end-stage renal failure?AUTONOMIC & AUTACOID PHARMACOLOGY, Issue 1 2005K. Leineweber Summary 1 Cyclic AMP formation has consistently been reported to be desensitized in various tissues including heart of animal models of end-stage renal failure (ESRF). In contrast, reports on desensitization of cAMP formation in ESRF patients remain contradictory. Whether this discrepancy results from a difference between human ESRF and its animal models or from the use of circulating blood cells in the human and various solid tissues in the animal studies, remains unclear. Therefore, we performed three studies with heart and platelets of ESRF patients undergoing haemodialysis or continuous ambulatory peritoneal dialysis and age- and gender-matched controls with normal renal function (n = 11,13 each). 2 In platelets from haemodialysis patients adenylyl cyclase activity in response to receptor-dependent and -independent agonists was reduced by ,30%, and this could be explained by an alteration at the level of adenylyl cyclase itself. However, no such desensitization was seen in platelets from peritoneal dialysis patients. 3 In hearts from ESRF patients undergoing haemodialysis, , -adrenoceptor density and subtype distribution, cAMP formation in response to the , -adrenoceptor agonist isoprenaline or various receptor-independent stimuli, were very similar to those in control patients but activity of G-protein-coupled receptor kinase was increased by ,20%. 4 We conclude that conflicting reports on the desensitization of cAMP formation between ESRF patients and ESRF animal models are not explained by the use of solid tissues in animal studies vs. circulating blood cells in patient studies. Rather desensitization of cAMP formation seems to be a less consistent feature of human ESRF than of its animal models. [source] Metabolic pathway of magnetized fluid-induced relaxation effects on heart muscleBIOELECTROMAGNETICS, Issue 8 2005Gayane Ayrapetyan Abstract The effect of magnetized physiological solution (MPS) on isolated, perfused snail heart muscle contractility, 45Ca uptake and intracellular level of cAMP, and cGMP was studied. The existence of the relaxing effect of MPS on heart muscle at room temperature (22 °C) and its absence in cold medium (4 °C) was shown. The MPS had a depressing effect on 45Ca uptake by muscles and intracellular cAMP content and an elevating effect on intracellular cGMP level. It is suggested that the relaxing effect of MPS on heart muscle is due to the decrease of intracellular Ca ions as the result of activation of cGMP-dependent Ca efflux. The MPS induced decrease of intracellular cAMP content can be considered as a consequence of intracellular Ca loss, leading to the Na,+,K-ATPase reactivation, and causing the decrease of the intracellular level of ATP, serving as a substrate and positive modulator of cyclase activity. Bioelectromagnetics © 2005 Wiley-Liss, Inc. [source] | ||||||||||||||||