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

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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)

Extracellular calcium at millimolar concentrations inhibits collective motility of ejaculated ram spermatozoa. In untreated cells, or when motility was made dependent upon glycolytic activity, there is very small inhibition, but when motility was made dependent upon mitochondrial respiration there is very high inhibition in motility by increasing extracellular Ca2+ concentration. Quercetin, which inhibits (Ca2+ + Mg2+)-ATPase activity in isolated plasma membranes, also inhibits motility mainly in cells that have been made dependent upon glycolytic activity, but there is also inhibition in untreated cells. When motility was made dependent upon mitochondrial activity, there is no inhibition but rather some stimulation in motility by quercetin. The inhibitory effect of quercetin is enhanced by increasing Ca2+ concentration in the medium. Quercetin also inhibits uptake of calcium into the cells, in a mechanism by which a calcium channel is involved. This inhibition is high only when the glycolysis is inhibited in the cells. The rate of glycolysis is decreased by quercetin or ouabain, but their effects on motility are quite different. Based on these data, it appears that the plasma membrane (Ca2+ + Mg2+)-ATPase or the Ca2+ pump have a functional role in the regulation of spermatozoa motility. This motility regulation is functioning through mechanisms which include glycolytic activity and maintenance of intracellular calcium concentrations.
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PMID:The role of calcium and Ca2+-ATPase in maintaining motility in ram spermatozoa. 293 27

Because of the potential of dihydropyridine calcium channel blockers in the management of premature labor, we have studied the direct effects of nitrendipine on actomyosin in the pregnant and nonpregnant uterus and in the term human placenta. Actomyosin adenosinetriphosphatase in the three tissues and another model of actin-myosin interaction, superprecipitation of placental actomyosin, were inhibited by nitrendipine. The inhibition was not diminished by high concentrations of calcium. To identify the mechanism, placental myosin was phosphorylated in the absence and presence of 0.8 X 10(-4) mol/L of nitrendipine. The myosin phosphorylated in the presence of nitrendipine had lower actin-activated adenosinetriphosphatase, which is consistent with the inhibition of myosin light chain phosphorylation. However, nitrendipine did not affect the adenosinetriphosphatase activity of myosin nor did further reduce the adenosinetriphosphatase of the already phosphorylated placental actomyosin. Thus nitrendipine inhibition is directed to the phosphorylation reaction but not to the adenosinetriphosphatase site of myosin. Myometrial relaxation in vivo or in vitro occurs at the pharmacologic nitrendipine levels of 10(-9) to 10(-8) mol/L, which is at least 10,000 times lower than that of the concentration of 50% inhibition of myosin light chain phosphorylation (0.0026 +/- 0.00015 mol/L of nitrendipine, mean +/- SEM) demonstrated in the present work. Because of this difference, the direct intracellular actions of dihydropyridine calcium channel blockers are not expected to cause adverse effects in the uteroplacental system when these drugs are used in the prevention or treatment of premature labor.
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PMID:Pharmacologic levels of nitrendipine do not affect actin-myosin interaction in the human uterus and placenta. 293 50

The Syrian cardiomyopathic hamster has a hereditary disease characterized by a progressive myocyte necrosis and intracellular calcium overload. Several systems in the heart sarcolemma that regulate the rate of Ca2+ entry or efflux were examined. There is a selective decrease of Ca2+-pumping ATPase activity in the heart sarcolemma of 40-day-old myopathic hamsters, while the Na+-Ca2+ exchange system and the ouabain-sensitive (Na+ + K+)-ATPase activity remain intact. This age-dependent decrease in Ca2+-ATPase activity closely parallels the time course of lesion development. Both the affinity for Ca2+ (Km) and the maximal velocity (Vmax) of the Ca2+-dependent ATP hydrolysis are altered. In addition, there is also an increased number of calcium channel receptor binding sites. Thus the data suggest that the imbalance in Ca2+ fluxes across the cardiac plasma membrane may be involved in the pathogenesis of this cardiomyopathy.
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PMID:Defective Ca2+-pumping ATPase of heart sarcolemma from cardiomyopathic hamster. 295 83

Hypertrophy is an adaptive mechanism of the heart subjected to pressure overload. Ultrastructural, electrophysiological and mechanical changes occur during this adaptation. A decrease in the inotropic responsiveness of the hypertrophied heart has often been observed as compared to the normal heart. Four sarcolemmal mechanisms that could account for this modification have been described. The mechanism of action of each system (calcium channel, alpha-and beta-adrenergic systems, (Na+,K+)-ATPase) of the hypertrophied heart has been compared to that of the normal heart. In spite of the paucity of results available relating to the calcium channel, the lengthening of the action potential in every case of compensatory hypertrophy could be explained by an altered functioning of the calcium channel. alpha- and beta-adrenergic systems in the hypertrophied heart could be modified at the receptor level itself, or at another level in the cascade of events under their control. For example, two different models of hypertrophy showed a decreased inotropic responsiveness correlated to a defect in the GS regulatory protein. The modification of the ouabain-receptor (Na+,K+)-ATPase mediates a decrease and a prolongation of the inotropic response. According to the modifications of each system, a direct relationship does not seem to exist between the stimulated membrane system and the inotropic responsiveness of the hypertrophied heart.
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PMID:Can changes in sarcolemmal membranes account for the altered inotropic responsiveness in hypertrophied heart? 295 94

The Ca2+-adenosine triphosphatase (ATPase) of skeletal muscle sarcoplasmic reticulum is a single protein species that pumps calcium ions at the expense of adenosine triphosphate (ATP). The reaction cycle includes phosphorylated intermediates which change the affinity and orientation of calcium sites. The monomer appears to be fully functional. Cross-linking and fluorescence studies indicate that ATP binds to a domain that approaches the phosphorylation site and becomes occluded during the reaction cycle. Interactions between these and the calcium channel, possibly via an energy transduction domain, ensure efficient coupling of catalytic and transport cycles.
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PMID:Mechanism of action of the calcium pump of sarcoplasmic reticulum of skeletal muscle. 296 Oct 95

Parietal cell secretory function may be inhibited by three mechanisms. (1) Receptors for gastrin, histamine and acetylcholine are present on the canine parietal cell, and parietal cell function may be directly inhibited by specific antagonists for each of these receptors. (2) Receptor activation of parietal cell function is mediated by cyclic AMP-dependent (histamine) and calcium-dependent (cholinergic agents and gastrin) mechanisms. The antisecretory action of prostaglandins reflect interference with histamine activation of adenylate cyclase. The current generations of calcium channel blockers have only weak antisecretory actions in vivo and are unlikely to be useful in clinical practice. (3) A third mechanism of inhibition is blockade of H+/K(+)-ATPase by substituted benzimidazoles, such as omeprazole. Each of these three mechanism provides modalities of potential clinical usefulness for treating acid-peptic disease. Gastrin and acetylcholine receptors are present on other fundic cells, in addition to the parietal cell. These other cells include the somatostatin cell in the dog fundic mucosa and the histamine-containing enterochromaffin-like (ECL) cell present in the fundic mucosa of several species. The relative impact of these receptors on different cell types on the regulation of acid secretion remains uncertain, and is probably variable among different species. One gastrin receptor of considerable importance is the gastrin receptor that exerts a trophic effect on the ECL cell in the fundic mucosa. Sustained hypergastrinaemia in response to profound hypochlorhydria is associated with hyperplasia of this cell type; the elucidation of the conditions that promote this hyperplasia and the clinical consequences of this association are pressing challenges.
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PMID:Review: antisecretory drugs: cellular mechanisms of action. 297 19

The messenger roles of cyclic AMP and the calcium ion in stimulus-secretion coupling are considered in the frog and bovine corneal epithelium, respectively. In the frog cornea, epinephrine stimulates net C1 transport by increasing cyclic AMP content. This stimulation is associated with a larger apical membrane C1 conductance and basolateral membrane ionic conductance. The response of the apical membrane conductance is thought to result from an increase in cyclic AMP content whereas the basolateral membrane ionic conductance increase is unrelated based on measurements of the effects of the calcium channel antagonist, diltiazem, and the beta agonist, isoproterenol, on the electrical parameters and cyclic AMP content. The basolateral membrane is essentially K permselective since the K channel blocker, Ba, depolarized the intracellular potential difference and increased the basolateral membrane resistance. Diltiazem had even larger effects on these parameters suggesting that this compound is a more effective inhibitor of K channel activity than barium. In broken cell preparations of bovine corneal epithelium, a high affinity form of Ca + Mg activated ATPase is present (Km = .06 microM for Ca) and is essentially of plasma membrane origin. This ATPase activation is at a Ca activity similar to the expected intracellular value and suggests that this activity is the enzymatic basis for net Ca transport.
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PMID:Roles of cyclic AMP and Ca in epithelial ion transport across corneal epithelium: a review. 299 Aug 18

Cardiac sarcolemmal membranes were isolated from the rat heart and their ability for Na+-Ca2+ exchange in the absence or presence of diltiazem and verapamil was examined. Maximal Ca2+ influx activity of membranes due to Na+-dependent reaction occurred within 3 min and was about 5 nmol Ca2+/mg protein. Diltiazem (0.1 to 10 microM) depressed the Ca2+ influx activity significantly whereas verapamil (0.1 to 10 microM) had no effect at initial stages of the reaction (10 to 20 sec). The inhibitory effect of diltiazem on Ca2+ influx was found to be of an uncompetitive nature. Sodium was found to cause a rapid Ca2+ efflux from the calcium loaded membrane vesicles; about 70% of the Ca2+ efflux activity was increased by 0.1 to 10 microM of verapamil and 10 microM of diltiazem significantly. The stimulatory effect of these agents on Ca2+ efflux was associated with a change in Ka value from 16 to 5 mM Na+. Both diltiazem (0.1-3 microM) and verapamil (0.1-10 microM) did not affect the membrane Na+-K+ ATPase activity, but diltiazem in high concentrations (10-30 microM) had an inhibitory action. Specific calcium channel blocking agents, nitrendipine and nifedipine, depressed sodium-dependent Ca2+-efflux activity. A beta-adrenoreceptor antagonist, propranolol, unlike acebutolol, increased sodium-induced Ca2+-influx at high concentrations (10-100 microM).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Modification of cardiac sarcolemmal Na+-Ca2+ exchange by diltiazem and verapamil. 299 25

Atrial natriuretic factor (ANF) inhibits basal and stimulated aldosterone synthesis in adrenal glomerulosa cells. ANF probably acts through specific membrane receptors. Alterations in cyclic GMP and cyclic AMP levels do not account for ANF's inhibitory effect. ANF does not block angiotensin II (AngII) receptors nor does it interfere with phosphoinositide metabolism or calcium movements stimulated by adrenal agonists. ANF does not inhibit protein synthesis nor does it work by inhibiting NA+,K+-ATPase or depleting cell potassium. ANF decreases conversion of endogenous cholesterol to pregnenolone, the step stimulated by adrenocorticotropin and AngII. ANF does not affect the conversion of 20-alpha-hydroxycholesterol, which easily penetrates mitochondrial membranes to the site of the cholesterol side-chain cleavage enzyme. These results suggest that ANF inhibits the ability of endogenous cholesterol to reach or interact with the side-chain cleavage enzyme. ANF does not act like a calcium channel-blocking agent. However, ANF is less effective at high-calcium concentrations, which suggests that it may inhibit a step that calcium stimulates. Understanding ANF action will probably require identification of the specific biochemical changes (mediators) that it induces. Parallel efforts to understand how other agents stimulate steroidogenesis (particularly in the areas of protein synthesis, protein phosphorylation, and cholesterol movements) will further this understanding.
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PMID:Inhibition of aldosterone synthesis by atrial natriuretic factor. 301 92

Effects of purified Mojave toxin on rat synaptic membrane (Ca+2 + Mg+2)-ATPase and dihydropyridine receptor were determined. The toxin was observed to stimulate specifically (Ca+2 + Mg+2)-ATPase approximately two-fold with no effect on Mg+2 dependent ATPase activity. Examination of the effects of increasing amounts of purified Mojave toxin on binding of the calcium channel blocker, nitrendipine, indicated that the addition of 10 micrograms (4.5 X 10(-10) moles) of toxin resulted in greater than 90% inhibition of nitrendipine binding. Furthermore, binding studies revealed the toxin to have little affinity for the ligand indicating its interaction with calcium channel components. Since Mojave toxin has associated with it a phospholipase A2 activity, we investigated the effects of 4-bromophenacylbromide, a known inhibitor of phospholipase A2 activity in order to discern the possible effects of the purified toxin on synaptic membranes. At concentrations previously shown to be inhibitory of purified phospholipase A2 from cobra venom, both ATPase activity and nitrendipine binding of synaptic membranes were significantly inhibited. Thus we cannot rule out the possibility that the endogenous phospholipase activity of the purified toxin is responsible for its effects on the rat brain synaptic functions studied here. Binding studies conducted in the presence of verapamil and diltiazem indicated that the toxin interacts with allosteric sites responsible for regulation of the binding of nitrendipine. Although we have not tested the effects of Mojave toxin on other ion channels and/or receptors, results presented here suggest the potential usefulness of this toxin as a molecular probe of the calcium channel complex.
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PMID:The effects of purified Mojave toxin on rat synaptic membrane (Ca+2 + Mg+2)-ATPase and the dihydropyridine receptor. 301 16


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