Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:4.6.1.2 (guanylate cyclase)
8,497 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Relaxation of the lower esophageal sphincter (LES) results from activation of its intrinsic innervation. This relaxation is associated temporally with an increase in the guanosine 3',5'-cyclic monophosphate (cGMP) content of the muscle. This study tests the hypothesis that variations in the production of cGMP mediate resting LES tone and nerve-induced relaxation. We examined the effects of guanylate cyclase inhibitors, such as cystamine and methylene blue (MB), on the resting tone, resting membrane potential, electrical field stimulation (EFS)-induced relaxation, and cGMP content of circular smooth muscle from the LES of the opossum. Strips of sphincter muscle were placed in a tissue bath and stretched to 125% resting length. Both cystamine and MB increased the resting tone of LES muscle in a concentration-dependent manner (EC50 = 1.1 +/- 0.2, n = 12, and 1.6 +/- 0.4 mM, n = 10, respectively). The increase in tone by cystamine was not blocked by tetrodotoxin, atropine, or propranolol. Cystamine (1 mM) did not alter the resting membrane potential of circular muscle cells of the LES. The removal of extracellular Ca2+ by the addition of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA, 4 mM) and nifedipine (1 microM) shortened the duration but not the amplitude of the response to cystamine. Pretreatment with caffeine (5 mM) in the presence of EGTA and nifedipine to deplete intracellular Ca2+ stores blocked the increase in tone by cystamine. Cystamine (1 mM) failed to inhibit LES relaxation induced by EFS. Carbachol, at a concentration that induced a similar increase in base-line tone, attenuated the nerve-mediated relaxation. Cystamine did not alter basal cGMP levels, but inhibited the rise in cGMP induced by EFS. The data indicate that cystamine increases LES tone but does not inhibit EFS-induced relaxation, even though it inhibits EFS-induced increases in cGMP content. The increase in tone is dependent on the presence of intracellular Ca2+ stores.
...
PMID:Guanylate cyclase inhibitors: effect on tone, relaxation, and cGMP content of lower esophageal sphincter. 135 4

This study evaluates the role of intracellular levels of Ca2+ [Ca2+]i in cyclic GMP formation mediated by muscarinic and histamine receptors in the mouse neuroblastoma clone N1E-115. Muscarinic agonists activated the turnover of phosphoinositides with a relative maximal response similar to that observed previously for cyclic GMP formation. Carbamylcholine induced a transient increase in inositol trisphosphate with a time course similar to that of cyclic GMP formation. In cells loaded with the fluorescent Ca2+ probe fura-2/acetoxymethyl ester, carbamylcholine as well as histamine induced a rapid and transient rise in [Ca2+]i. The time course of the changes in [Ca2+]i induced by agonists as well as by ionomycin closely paralleled that of cyclic GMP formation. Chelation of [Ca2+]i by loading of N1E-115 cells with quin 2/acetoxymethyl ester inhibited cyclic GMP formation induced by agonists in a dose-dependent manner. When cyclic GMP formation induced by agonists was assayed after the cells were exposed to 3 mM ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) for 2 min, the formation of cyclic GMP was not inhibited significantly; however, it was completely abolished after 30-min exposure to EGTA. Treatment of cells with phospholipase A2 had no effect on resting [Ca2+]i and only slightly increased cyclic GMP formation, in spite of the induction of a marked release of [3H]arachidonate. Moreover, the formation of cyclic GMP induced by ionomycin was inhibited by the addition of phospholipase A2. Melittin contaminated with phospholipase A2 activity induced a rapid and sustained increase in cyclic GMP formation, as well as unesterified [3H]arachidonate release. However, after inactivation of the phospholipase A2 activity of melittin, its ability to stimulate cyclic GMP formation was enhanced. Our data indicate that receptor agonists stimulate cyclic GMP formation in N1E-115 cells by activating the formation of inositol trisphosphate, which is followed by the release of Ca2+ from intracellular stores. The evidence obtained does not support a major role for arachidonate release in receptor-mediated activation of guanylate cyclase. Conversely, it is consistent with an inhibitory role for arachidonic acid or its metabolites in this process.
...
PMID:Role of intracellular Ca2+ mobilization in muscarinic and histamine receptor-mediated activation of guanylate cyclase in N1E-115 neuroblastoma cells: assessment of the arachidonic acid release hypothesis. 197 74

The purified membrane-bound form of guanylate cyclase was incorporated into artificial unilamellar phospholipid vesicles. The rate and extent of enzyme incorporation into the vesicles was dependent upon the phospholipid concentration and the time period of incubation. The enzyme was incorporated at a significantly faster rate after removal of carbohydrate with endoglycosidase H. The incorporation of the enzyme led to a 10-fold decrease in the apparent maximal velocity and a 2-fold increase in the apparent Michaelis constant for MnGTP. Extraction of liposomes containing guanylate cyclase with 0.2% Lubrol PX resulted in the recovery of 85% of the original amount of added activity, suggesting that the decrease in maximal velocity was not due to enzyme denaturation. Phosphatidylcholine liposomes differentially effected the activity of the membrane-form of guanylate cyclase, dependent on the nature of the fatty acid present on the phospholipid. Specific activities ranged between 458 nmol/min per mg and 2.6 mumol/min per mg, dependent upon the fatty acids present. Liposomes containing the membrane-bound form of guanylate cyclase were subsequently fused with erythrocytes using poly(ethylene glycol) 4000 in attempts to introduce the enzyme into intact cells. The enzyme was successfully introduced into the erythrocytes; greater than 90% of the enzyme activity was subsequently shown to be associated with erythrocyte membranes. Cyclic GMP concentrations of erythrocytes increased from essentially nondetectable to 4 pmol/10(9) cells after introduction of the enzyme. These results demonstrate that guanylate cyclase can be incorporated into liposomes in an active state and that such liposomes can be used to introduce the enzyme into cells where it can subsequently function to generate cyclic GMP.
...
PMID:The incorporation of a purified, membrane-bound form of guanylate cyclase into phospholipid vesicles and erythrocytes. 285 74

Intestinal brush border guanylate cyclase was previously reported to be activated by the Escherichia coli enterotoxin (STa). This system was reexamined in order to develop a hypothesis for the mechanism of activation. The extent of activation was previously underestimated, since by using sodium azide to inhibit competing reactions and ethylene glycol bis(beta-aminoethyl ether) N,N-tetraacetic acid to chelate Ca2+, which is inhibitory, maximal activations of 30- to 50-fold were obtained. Ca2+ inhibition was only partially relieved by the calmodulin inhibitor calmidazolium. Inhibitors of the O2-dependent activation of soluble guanylate cyclase had no effect on STa activation; hence, it was concluded that STa activation did not involve arachidonate release and oxidation. STa was able to further increase activity already elevated by the nonionic detergent Lubrol PX. The membrane-active agent filipin, which was previously reported to inhibit both basal and agonist-stimulated adenylate cyclase, did not inhibit STa activation of guanylate cyclase. Digitonin, another cholesterol binder, inhibited STa activation at low concentrations, which disappeared at higher concentrations. Both of these agents stimulated basal activity. Dimethyl sulfoxide produced a concentration-dependent inhibition of STa activation, while increasing basal activity 7-fold. Ethanol inhibited both basal and STa-stimulated activity, with the former being more affected. Benzyl alcohol, like ethanol, a "fluidizer" of cell membranes, also inhibited both basal and activated enzymes. We concluded that STa directly activates this guanylate cyclase and, because of the differential effects of inhibitors on basal and STa-stimulated activity, propose a receptor-mediated mechanism.
...
PMID:Characterization of intestinal brush border guanylate cyclase activation by Escherichia coli heat-stable enterotoxin. 286 96

The mechanism of activation of intestinal guanylate cyclase by Escherichia coli heat-stable enterotoxin (STa) has been studied by using isolated rat intestinal epithelial cells and purified brush border membrane (BBM) preparations. Inhibitors of prostaglandin biosynthesis, quinacrine and 5,8,11,14-eicosatetraynoic acid (ETYA), significantly reduced intracellular levels of cyclic guanosine 3', 5'-monophosphate in isolated cells treated with STa. Although these data suggested that activation of phospholipase A2 and metabolism of arachidonic acid are involved in the mechanism of action of STa, other data ruled out such a mechanism. (i) The rate of release of [3H]arachidonic acid by prelabeled intestinal cells incubated with STa was the same as control cells not treated with STa. (ii) Thin-layer chromatography of lipid extracts of intestinal cells treated with STa and untreated cells did not reveal any quantitative or qualitative differences in free fatty acids, neutral lipids, and phospholipids. (iii) Amounts of prostaglandin PGE2, prostaglandin PGF2 alpha, and thromboxane B2 in intestinal cells and BBM incubated with STa did not increase compared with controls not incubated with STa. When purified BBM preparations were incubated with phospholipase A2 inhibitors (p-bromophenacyl bromide and quinacrine) or cyclooxygenase inhibitors (ETYA and indomethacin), basal and STa-induced guanylate cyclase activities were significantly reduced. Inhibitors of calcium-calmodulin-mediated reactions (EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N,N-tetraacetic acid], trifluoperazine, and chlorpromazine) and calcium channel blockers (verapamil and nifedipine) also nonspecifically inhibited both basal and STa-stimulated guanylate cyclase in BBM preparations. Lanthanum, a competitive inhibitor of membrane-bound calcium, did not affect either basal or STa-stimulated guanylate cyclase of BBM preparations.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Characterization of the mechanism of action of Escherichia coli heat-stable enterotoxin. 614 30

The mechanisms by which two nitrogen monoxide (NO) generators, hydroxylamine and S-nitroso-L-cysteine (NO-CYS), induce hippocampal [3H]norepinephrine ([3H]NE) release was investigated. Neither hydroxylamine- nor NO-CYS-induced release was affected by the guanylate cyclase inhibitors, methylene blue or LY 83,583. The effect of hydroxylamine was completely dependent on extracellular Ca++ and reduced by 40% in the presence of omega-conotoxin GVIA, an N-type Ca(++)-channel antagonist; however it was unaffected by Ni++, nifedipine, caffeine or thapsigargin. The stimulatory effect of hydroxylamine on hippocampal cyclic GMP formation was not significantly affected by removal of extracellular Ca++, indicating that Ca(++)-dependent release is not due to inhibition of NO formation from hydroxylamine. However, the response to NO-CYS was reduced by 35 to 50% in either nominally Ca(++)-free or 10 mM MgSO4-containing buffer. Interestingly, buffer containing ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid dramatically enhanced the formation of NO from NO-CYS and potentiated the NO-CYS response. Both NO-CYS- and hydroxylamine-induced [3H]NE release was inhibited by NE transport blockers, indicating a prominent role for reverse transport. NO-CYS completely inhibited synaptosomal uptake of [3H]NE (IC50 approximately, 300 microM). NO generator-induced [3H]NE release has a glutamate-dependent component (see accompanying article). Inhibition of glutamate-evoked [3H]NE release by mazindol, an inhibitor of NE transport, suggests that the glutamate-dependent component also involves reversal of the NE transporter. These data suggest that NO produced from hydroxylamine or NO-CYS evoke both vesicular and nonvesicular release of hippocampal [3H]NE. Putative NO target molecules and the role of extracellular Ca++ are discussed.
...
PMID:Characterization of nitric oxide generator-induced hippocampal [3H]norepinephrine release. II. The role of calcium, reverse norepinephrine transport and cyclic 3',5'-guanosine monophosphate. 756 42

This study aimed to examine the role of nitric oxide (NO) in the regulation of renin secretion from renal juxtaglomerular (JG) cells. Using primary cultures of mouse renal JG cells, we found that sodium nitroprusside (SNP) and 3-morpholino-sydnonimin-hydrochloride (SIN-1), two structurally different liberators of NO, led to a transient inhibition during the first hour followed by a marked dose-dependent stimulation of renin secretion lasting for an additional 20 h. This stimulatory effect was blunted by methylene blue (50 microM) and was reversible within minutes after removal of the NO liberators. SNP and SIN-1 also stimulated guanylate cyclase activity in the cultures with a maximum within the first hour of incubation. Increasing intracellular guanosine 3',5'-cyclic monophosphate levels by 8-(4-chlorophenylthio)guanosine 3',5'-cyclic monophosphate (100 microM) or by atrial natriuretic peptide (10 nM) decreased basal renin secretion but did not inhibit the effect of SNP. The stimulatory effect of SNP was not related to adenosine 3',5'-cyclic monophosphate levels in the JG cells and was blunted after chelation of extracellular calcium by 2 mM ethylene glycol-bis(beta-amino-ethyl ether)-N,N,N'N'-tetraacetic acid. Taken together, our findings suggest that liberators of NO have two effects on renin secretion from isolated JG cells: an inhibitory effect mediated by stimulation of soluble guanylate cyclase activity and a stimulatory effect mediated by an as yet unknown pathway that requires extracellular calcium.
...
PMID:Liberators of NO exert a dual effect on renin secretion from isolated mouse renal juxtaglomerular cells. 839 40

Superoxide plays a role in blood pressure regulation in certain vascular diseases, however, its involvement in regulating basal blood pressure is uncertain. Vascular superoxide concentrations are limited by extracellular superoxide dismutase (EC-SOD), which is highly expressed in the vasculature of most animal species. Metalloporphyrins are low molecular weight, synthetic, redox-active, catalytic antioxidants that act as SOD mimetics. We evaluated the effects of metalloporphyrins on blood pressure in different animal species. The metalloporphyrin AEOL10113 (5-10 micro /kg iv), but not native or polyethylene glycol-CuZnSOD, caused a dose-dependent reduction in blood pressure in anesthetized rats. AEOL10113 had no effect on blood pressure in mice (wild-type or EC-SOD knockouts), guinea pigs, dogs, or baboons at doses up to 5 mg/kg iv Structure-activity studies indicated that metalloporphyrins with high SOD activity were more effective in lowering rat blood pressure than low-activity analogs. The blood pressure effect of AEOL10113 was not attributable to the release of manganese, nor was it affected by inhibitors of nitric oxide synthase (L-NAME) and guanylate cyclase (ODQ, 8-bromo-cGMP, and methylene blue) or nitric oxide scavengers (HbAo). Chlorpheniramine attenuated the effect, suggesting that the blood pressure response in rats is related to histamine release rather than the protection of nitric oxide.
...
PMID:Hemodynamic effects of metalloporphyrin catalytic antioxidants: structure-activity relationships and species specificity. 1248 34

Carbon monoxide (CO) is most often thought of as an exogenous toxin rather than as a possible endogenous nootrope. However, a limited number of studies have suggested that CO is necessary in memory processing for at least some tasks. While nitric oxide (NO) and CO are known activators of guanylyl cyclase (GC), only the effect of NO on GC has been extensively investigated as a mechanism underlying memory processing. The aim of the present study was to determine if inhibition of CO production would have an effect on memory processing. Using chicks trained on a single trial passive avoidance task, inhibition of CO production using zinc (II) deuteroporphyrin IX 2,4-bis ethylene glycol (ZnBG; 5 microM) resulted in two transient retention losses occurring at around 40 and 130 min post-training. The timing of these transient retention losses was similar to those observed following inhibition of GC, using the same species and task in a previous study. This supports the notion that CO is necessary in memory processing for this task and may act through a GC-dependent mechanism. As ZnBG also directly inhibits GC or nitric oxide synthase (NOS) at high concentrations, a second experiment was carried-out to confirm the specificity of ZnBG for heme oxygenase (HO) at the concentration used. The action of ZnBG was challenged with the HO agonist hemin (100 microM) and the transient deficits were abolished. This confirmed that the action of ZnBG on memory was through a CO-related mechanism rather than directly on GC or NOS. In this way the specificity of ZnBG (5 microM) for HO could be confirmed. The results support a role for endogenous CO in memory processing, possibly through activation of GC. In addition, the transient retention losses observed following administration of ZnBG suggest that CO may be necessary for memory retrieval and not formation as previously thought.
...
PMID:Inhibition of endogenous carbon monoxide production induces transient retention losses in the day-old chick when trained using a single trial passive avoidance learning task. 1582 Aug 60

In numerous vascular beds, acetylcholine (ACh) evokes the simultaneous release of endothelium-derived relaxing and contracting factors (EDRF and EDCF, respectively). We aimed to determine whether ACh evokes the release of an EDCF in the chicken ductus arteriosus (DA) and to identify its nature. Isolated rings DA from 19-d chicken embryos (total incubation: 21-d) were studied in a wire myograph. Low concentrations of ACh (30 nM-1 microM) elicited a relaxation, which was followed by a contraction at higher concentrations (3 microM-0.1 mM). Both relaxation and contraction were abolished by removal of endothelium and were sensitive to the antimuscarinic agents atropine and 4-DAMP (M3-receptor antagonist). ACh-induced contraction was impaired in the presence of the non-selective inhibitor of cyclooxygenase (COX) indomethacin, the selective COX-1 inhibitor valeryl salicylate, and the thromboxane (TX)/prostaglandin (PG) H2 (TP) receptor blocker SQ-29458, whereas the response was not affected by the selective COX-2 inhibitor nimesulide, the TX synthase inhibitor furegrelate, the H2O2 scavenger PEG-catalase, the nitric oxide synthase inhibitor L-NAME, or the soluble guanylate cyclase inhibitor ODQ. Enzyme immunoassay determined that, under basal conditions, the chicken DA produced PGE2, PGF2alpha and TXB2 (stable metabolite of TXA2). Prostanoid production was inhibited by indomethacin but was not significantly affected by ACh. We conclude that in the chicken DA, stimulation of muscarinic receptors by ACh induces an endothelium-dependent relaxation followed by an endothelium-dependent contraction. The contraction involves COX-1 activation and TP receptor stimulation.
...
PMID:Endothelium-dependent contraction induced by acetylcholine in the chicken ductus arteriosus involves cyclooxygenase-1 activation and TP receptor stimulation. 2048 53


1 2 Next >>

---