Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Snake venom cardiotoxins have been recently shown to block the enzymatic activity of phospholipid protein kinase and Na+,K+-ATPase. To understand the molecular basis for the inhibitory effects of cardiotoxin on the action of these enzymes, the nucleotide triphosphate binding ability of cardiotoxin analogue II (CTX II) from the Taiwan cobra (Naja naja atra) venom is investigated using a variety of spectroscopic techniques such as fluorescence, circular dichroism, and two-dimensional NMR. CTX II is found to bind to all the four nucleotide triphosphates (ATP, UTP, GTP, and CTP) with similar affinity. Detailed studies of the binding of dATP to CTX II indicated that the toxin molecule is significantly stabilized in the presence of the nucleotide. Molecular modeling, based on the NOEs observed for the dATP.CTX II complex, reveals that dATP binds to the CTX II molecule at the groove enclosed between the N- and C-terminal ends of the toxin molecule. Based on the results obtained in the present study, a molecular mechanism to account for the inhibition of the enzymatic activity of the phospholipid-sensitive protein kinase and Na+,K+-ATPase is also proposed.
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PMID:Binding of nucleotide triphosphates to cardiotoxin analogue II from the Taiwan cobra venom (Naja naja atra). Elucidation of the structural interactions in the dATP-cardiotoxin analogue ii complex. 1036 32

Depletion of Ca(2+) stores in the sarcoplasmic reticulum (SR) activates extracellular Ca(2+) influx via capacitative Ca(2+) entry (CCE). Here, CCE levels in proliferating and growth-arrested human pulmonary artery smooth muscle cells (PASMCs) were compared by digital imaging fluorescence microscopy. Resting cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)) in proliferating PASMCs was twofold higher than that in growth-arrested cells. Cyclopiazonic acid (CPA; 10 microM), which inhibits SR Ca(2+)-ATPase and depletes inositol 1,4,5-trisphosphate-sensitive Ca(2+) stores, transiently increased [Ca(2+)](cyt) in the absence of extracellular Ca(2+). The addition of 1.8 mM Ca(2+) to the extracellular solution in the presence of CPA induced large increases in [Ca(2+)](cyt), indicative of CCE. The CPA-induced SR Ca(2+) release in proliferating PASMCs was twofold higher than that in growth-arrested cells, whereas the transient rise of [Ca(2+)](cyt) due to CCE was fivefold greater in proliferating cells. CCE was insensitive to nifedipine but was significantly inhibited by 50 mM K(+), which reduces the driving force for Ca(2+) influx, and by 0.5 mM Ni(2+), a putative blocker of store-operated Ca(2+) channels. These data show that augmented CCE is associated with proliferation of human PASMCs and may be involved in stimulating and maintaining cell growth.
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PMID:Cell proliferation is associated with enhanced capacitative Ca(2+) entry in human arterial myocytes. 1044 11

Current methods of detection for fish and shellfish biotoxins in monitoring and research purposes are either labor intensive, expensive, require specialized techniques or all of the above. This paper reports on the development of a fairly sensitive, rapid, and inexpensive assay which detects the presence of compounds that affect the sodium channel. It is based on the principles of the mouse neuroblastoma tissue culture assay for sodium channel specific-biotoxins using red blood cells (RBCs) from the red tilapia (Sarotherodon mossambicus). This assay has the potential to complement the use of live animal bioassay testing for marine toxins. Veratridine, a sodium channel activator and ouabain, an inhibitor of Na(+)/K(+) ATPase, both react with the tilapia RBCs by affecting the permeability of the cell's membrane. Saxitoxin (STX), its analogs, and tetrodotoxin (TTX) can inhibit the action of veratridine and ouabain leaving the cell morphologically normal. By sequencing the addition of veratridine and ouabain, with either the extracted samples, saxitoxin, tetrodotoxin, or ciguatoxin (CTX-a sodium channel activator) to the RBCs a sodium channel antagonist or activator can be detected. Results using pure concentrations of a sodium channel-specific toxin could be detected to inhibit hemolysis at a concentration of 0.3 microg/ml STX, 3.5 microg/ml for neo-STX, 3.0 microg/ml for GTX, and 5.0 microgl for TTX in the presence of ouabain and veratridine. CTX was detected at a concentration of 50 microg/ml. The RBCs from the red tilapia was used due to the fish's ability to osmoregulate its internal environment to survive in both fresh and saltwater. In addition, with growing opposition to live animal testing, this assay has been designed as a non-lethal means of testing for sodium channel affecting marine toxins. No test animals are sacrificed and blood may be drawn from the same fish for continued sample testing.
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PMID:A rapid hemolysis assay for the detection of sodium channel-specific marine toxins. 1111 65

In the excised Langendorff-perfused rat whole-heart preparation, a linear relation between left ventricular myocardial oxygen consumption per beat (Vo2) and systolic pressure-volume area (PVA, a total mechanical energy per beat) is obtained from a curved end-systolic pressure-volume relation as in the blood-perfused preparation. The ordinate Vo2 intercept of the Vo2-PVA relation is composed of Vo2 for total Ca2+ handling in the excitation-contraction coupling and basal metabolism. The Vo2 for total Ca2+ handling is mainly consumed by sarcoplasmic reticulum (SR) Ca2+ -ATPase. The aim of the present study was to investigate, in terms of left ventricular mechanoenergetics, how an inhibition of SR Ca2+ -ATPase by cyclopiazonic acid (CPA; 4 micromol/l) affects Ca2+ handling mechanisms in the excised Langendorff-perfused rat whole-heart preparation. The short-term (for 3 to 6 min after onset of the infusion) CPA infusion decreased Vo2 proportionally to the decrease in PVA. The long-term (for 9 to 12 min after the short-term CPA infusion) CPA infusion gradually increased Vo2 almost to the control level with an increase in PVA. The increases in both Vo2 and PVA during this infusion were completely abolished by a Na+/Ca2+ exchanger inhibitor, 3'9,4'9-dichlorobenzamil, indicating the contribution of Na+/Ca2+ exchanger to the increases in Vo2 and PVA. The O2 cost of left ventricular contractility during the long-term CPA infusion was significantly higher than during the short-term CPA infusion. All these results suggest the possibility of the contribution of greater energy-wasting Ca2+ extrusion processes (such as Na+/K+-ATPase coupled to the Na+/Ca2+ exchanger; its stoichiometry is 1 ATP : 1 Ca2+ to the larger oxygen cost of left ventricular contractility.
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PMID:Oxygen wasting for Ca2+ extrusion activated by partial inhibition of sarcoplasmic reticulum Ca2+ -atpase by cyclopiazonic acid in rat left ventricles. 1128 1

Inhibiting Ca(2+) uptake by the sarcoendoplasmic reticular Ca(2+)-ATPase pump (SERCA) causes release of Ca(2+) from the endoplasmic reticulum (ER), increased cytosolic Ca(2+) ([Ca(2+)](cyt)) and depletion of ER Ca(2+) stores. These studies were designed to test the effects of SERCA inhibition on neuronal viability, using as a model the human neuroblastoma cell line, SH-SY5Y. Continuous exposure to the SERCA inhibitor thapsigargin (TG) decreased SH-SY5Y viability to <30% after 48 h exposure, and produced DNA laddering. Two other SERCA inhibitors, BHQ and cyclopiazonic acid CPA, were similarly toxic, although at 1000-fold higher concentrations. BHQ and CPA toxicity was prevented by removing drug within several hours, whereas TG toxicity was essentially irreversible. All three SERCA inhibitors caused an increase in [Ca(2+)](cyt) that was partially blocked by the ryanodine receptor inhibitors, dantrolene and DHBP. Pretreatment with 40 microM dantrolene gave substantial protection against TG- or BHQ-induced cell death but it did not inhibit death from staurosporine, which does not cause release of ER Ca(2+). DHBP (20-100 microM) also gave partial protection against TG toxicity, as did ruthenium red (2 microM), but not ryanodine (10 microM). Inhibition of capacitative Ca(2+) entry with EGTA or LaCl(3) or low extracellular Ca(2+), or chelation of [Ca(2+)](cyt) with BAPTA-AM, failed to inhibit TG toxicity, although they prevented increases in [Ca(2+)](cyt) caused by TG. Taken together, these data suggest that toxicity caused by SERCA inhibition in SH-SY5Y cells is caused by ER Ca(2+) depletion, which triggers an apparent apoptotic pathway.
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PMID:Depletion of intracellular calcium stores is toxic to SH-SY5Y neuronal cells. 1175 Sep 1

Effects of tetrandrine (TET), a bisbenzylisoquinoline alkaloid, on the contractile responses of perfused rat mesenteric arteries to phenylephrine (PE) and caffeine were investigated. TET concentration-dependently (1-30 micro M) attenuated phenylephrine-induced responses but potentiated the contractile responses to caffeine (5-40 mM) in the presence and absence of Ca(2+). Berbamine (BER), a structural analogue of TET, elicited a relatively smaller inhibitory effect on the responses to PE due to Ca(2+) release or Ca(2+) influx. However, both TET and BER elicited a comparable potentiating effect on caffeine-induced contraction. Cyclopiazonic acid (CPA; 10 micro M), a selective sarcoplasmic reticulum Ca(2+)-ATPase pump inhibitor, mimicked the potentiating effect of TET when added 5 min prior to caffeine in Ca(2+)-free medium. However, CPA did not augment and might even inhibit the caffeine-induced response when it was preincubated with the tissue for 25 min prior to the addition of caffeine. We propose that TET elicits differential effects on PE- and caffeine-induced responses in perfused rat mesenteric arterial bed. The inhibitory effect of TET on PE-induced responses is probably due to its direct interactions with alpha-adrenoceptors and PE-sensitive Ca(2+)-channels. The augmentation of caffeine-induced responses by TET, particularly in Ca(2+)-free medium, is likely to be due to its partial inhibition of the sarcoplasmic reticulum Ca(2+)-ATPase pump.
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PMID:Tetrandrine potentiates caffeine-induced contraction but inhibits phenylephrine-induced contraction in perfused rat mesenteric artery. 1244 4

Calcium is a crucial regulator of many physiological processes such as cell growth, division, differentiation, cell death and apoptosis. In this study, we examined the effect of cGMP on agonist-induced [Ca(2+)](i) transient in isolated rat aortic endothelial cells. 100 microM ATP was applied to the cells bathed in a Ca(2+)-free physiological solution to induce a [Ca(2+)](i) transient that was caused by Ca(2+) release from intracellular stores. cGMP, which was applied after [Ca(2+)](i) reached its peak level, accelerated the falling phase of [Ca(2+)](i) transient. Pre-treatment of the cells with CPA abolished the accelerating effect of cGMP on the falling phase of [Ca(2+)](i) transient. The effect of cGMP was reversed by KT5823, a highly specific inhibitor of protein kinase G. Taken together, these data suggest that cGMP may reduce [Ca(2+)](i) level by promoting Ca(2+) uptake through sarcoplasmic/endoplasmic reticulum ATPase and that the effect of cGMP may be mediated by protein kinase G.
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PMID:cGMP stimulates endoplasmic reticulum Ca(2+)-ATPase in vascular endothelial cells. 1289 26

5-Hydroxytryptamine (5-HT) is a potent pulmonary vasoconstrictor and contributes to hypoxic pulmonary vasoconstriction and pulmonary arterial hypertension. Small intrapulmonary vessels are very sensitive to hypoxia and play a major role for blood flow regulation in the lung. Thus we have investigated the mechanisms involved in the calcium signal to 5-HT in rat small intrapulmonary artery (IPA). Effects of 5-HT were examined in isolated IPA (external diameter <250 microm) from rat. Digital imaging with fura-PE3 was used to record intracellular calcium concentration ([Ca(2+)](i)) and to follow external diameter of the vessels. 5-HT induced a sustained [Ca(2+)](i) variation that was sensitive to the inhibitor of the 5-HT(2A) receptors, ketanserin, and insensitive to voltage-dependent L-type calcium channel blockers (nitrendipine and nicardipine) or voltage-independent calcium channel antagonists (LOE-908, SKF-96365, and gadolinium). The calcium response to 5-HT was also not modified by a sarcoplasmic reticulum Ca(2+)-ATPase inhibitor (cyclopiazonic acid; CPA), which depletes intracellular calcium stores. CPA alone activated a capacitative calcium channel that was sensitive to LOE-908 and insensitive to SKF-96365 and gadolinium. The sustained calcium signal to 5-HT was partly blocked by inhibitors of arachidonic acid production (RHC-80267 and isotetrandrine) and mimicked by application of exogenous arachidonic acid. These results suggest that activation of a noncapacitative, arachidonic acid-sensitive, receptor-operated calcium channel contributes to 5-HT-induced sustained calcium increase in small IPA.
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PMID:5-HT induces an arachidonic acid-sensitive calcium influx in rat small intrapulmonary artery. 1475 48

The aim of the present study was to investigate the direct effects and action mechanisms of digitalis on the production of corticosterone in rat adrenocortical cells. Male rats were challenged with digoxin (1 microg ml(-1) kg(-1)) in the presence or absence of adrenocorticotropin (ACTH, 5 microg ml(-1) kg(-1)) administered by intravenous injection to the right jugular vein. Blood samples were collected at 0, 30, 60, and 120 min following the challenge. The concentration of corticosterone in the rat plasma samples was measured by radioimmunoassay. Zona fasciculata-reticularis (ZFR) cells in male rats were prepared and then incubated with or without digoxin or digitoxin in the presence or absence of ACTH (10(-9) m), forskolin (10(-7) m), 8-bromo-cyclic 3' : 5'-adenosine monophosphate (10(-4) m), cyclopiazonic acid (CPA, 10(-5) m), trilostane (10(-6) m), 25-OH-cholesterol (10(-5) m), pregnenolone (10(-5) m), progesterone (10(-5) m), or deoxycorticosterone (10(-5) m) at 37 degrees C for 1 h before collection of the media. Corticosterone or pregnenolone levels were measured by radioimmunoassay. A single injection of digoxin did not alter the basal level of plasma corticosterone, but did inhibit the level of plasma corticosterone released in response to ACTH in vivo. Administration of digoxin or digitoxin decreased both spontaneous and ACTH-stimulated release of corticosterone in vitro. Digoxin (10(-7)-10(-5) m) and digitoxin (10(-7)-10(-5) m), but not ouabain (10(-7)-10(-5) m), dose-dependently inhibited corticosterone production in response to forskolin and 8-Br-cyclic AMP in rat ZFR cells. Both digoxin (10(-6)-10(-5) m) and digitoxin (10(-6)-10(-5) m) attenuated corticosterone production in response to CPA. Digoxin (10(-5) m) or digitoxin (10(-5) m) inhibited cytochrome P450 side-chain cleavage enzyme (cytochrome P450scc) activity (catalyses conversion of cholesterol to pregnenolone in the presence of trilostane) in rat ZFR cells. The enzyme activity of 11 beta-hydroxylase (catalyses conversion of deoxycorticosterone to corticosterone) in ZFR cells was also inhibited by the administration of digoxin (10(-5) m) or digitoxin (10(-5) m).10 These results together suggest that digoxin and digitoxin decrease the release of corticosterone by acting directly on ZFR cells via a Na+, K+-ATPase-independent mechanism involving the inhibition of the activities of adenylyl cyclase, cytochrome P450scc and 11 beta-hydroxylase, as well as the functioning of cyclic AMP and intracellular calcium.
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PMID:Inhibitory effects of digoxin and digitoxin on corticosterone production in rat zona fasciculata-reticularis cells. 1524 23

Previously we have described the properties of store-operated channel currents (SOCs) in freshly dispersed rabbit portal vein smooth muscle cells. In addition to Ca(2+) store depletion these SOCs could also be activated by alpha-adrenoceptor stimulation and diacylglycerol (DAG) via a protein kinase C (PKC)-dependent mechanism. In the present study we have investigated the effect of beta-adrenoceptor stimulation on SOCs in rabbit portal vein myocytes. With whole-cell recording the selective beta-adrenoceptor agonist isoprenaline reduced the current evoked by cyclopiazonic acid (CPA, sarcoplasmic/endoplasmic reticulum ATPase inhibitor) by over 85%. With cell-attached patch recording, bath application of isoprenaline produced a pronounced inhibition of SOC activity evoked by either CPA or the acetoxymethyl ester form of BAPTA (BAPTA-AM). SOC activity evoked by CPA, the DAG analogue, 1-oleoyl-acetyl-sn-glycerol (OAG) or the phorbol ester, phorbol-12,13-dibutyrate (PDBu) was also markedly inhibited by the adenylate cyclase activator, forskolin, and the cell-permeable non-hydrolysable analogue of cyclic adenosine monophosphate (cAMP), 8-Br-cAMP. With inside-out patches, bath application of PDBu evoked channel currents with similar properties to SOCs which were inhibited by over 90% by a catalytic subunit of protein kinase A (PKA) and by 8-Br-cAMP. Moreover bath application of PKA inhibitors, H-89, KT5720 and an inhibitory peptide to quiescent cell-attached or inside-out patches, activated channel currents with similar properties to SOCs. These data suggest that in rabbit portal vein myocytes, stimulation of beta-adrenoceptors inhibits SOC activity via a cAMP-dependent protein kinase signal transduction cascade. In addition it is concluded that constitutive PKA activity has a profound inhibitory effect on SOC activity in this vascular preparation.
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PMID:Stimulation of beta-adrenoceptors inhibits store-operated channel currents via a cAMP-dependent protein kinase mechanism in rabbit portal vein myocytes. 1552 35


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