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)

Mg-independent Ca-ATPase activity was measured in secretory granules, mitochondria and microsomes from albino mouse islets and in secretory granules from noninbred ob/ob mouse islets. The enzyme existed in a high-affinity (Km for Ca2+ approx. 10(-7) M) and a low-affinity (Km approx. 10(-5) M) form. In all subfractions the high-affinity Ca-ATPase was inhibited by cyclic AMP, caffeine and Na+. Alloxan stimulated the microsomal Ca-ATPase by 25%, but had no effect on Ca-ATPase activity in granules and mitochondria. Glucose and glucose metabolites had no effect on Ca-ATPase in the secretory granule fraction from ob/ob mouse islets, whereas NADH inhibited the enzymes by 35%. The secretory granule Ca-ATPase was also inhibited by pCMBS (43%), chlorpromazin (87%) and ruthenium red (23%). 45Ca uptake was studied in secretory granules isolated from ob/ob mouse islets. The uptake was accelerated by addition of ATP, the maximum effect being found at 1 to 2 mM ATP. Omission of MgCl2 decreased the uptake by 25%. 45Ca uptake was abolished in the presence of pCMBS and chlorpromazine, whereas caffeine had no effect. The importance of Ca-ATPase in 45Ca transport and regulation of insulin release is discussed.
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PMID:Ca-ATPases in pancreatic islets. 645 Jan 52

The influence of 2-[(2-methoxy-4-methylsulfinyl)phenyl]-1H-imidazo[4,5-b]pyridine (AR-L 115 BS) and caffeine on Ca++-ATPase activity, Ca++-uptake and Ca++-release (efflux greater than influx:release) of the vesicles of sarcoplasmic reticulum of pig heart was investigated. In contrast to caffeine, 1 mmol/l AR-L 115 BS produced partial inhibition of Ca++-uptake of the vesicle while Ca++-release was only slightly affected. It was not possible to determine the effect of high concentrations of AR-L 115 BS and caffeine on the Ca++-ATPase activity because these substances showed a marked interference with the reagents of the reaction mixture.
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PMID:[Mechanism of action of AR-L 115 BS compared to caffeine]. 645 94

Pumiliotoxins (PTX) A, B, and 251D, members of a new class of indolizidine alkaloids isolated from the skin of poison frogs of the family Dendrobatidae, inhibit Ca2+-ATPase activity in sarcoplasmic reticulum vesicles from frog and rat hind-limb muscles. PTX-B and PTX-A appear to be relatively specific inhibitors of Ca2+-ATPase; PTX-A is much less potent than PTX-B. PTX-251D is a potent inhibitor of Ca2+-ATPase, and was also found to inhibit Na+, K+, and Mg2+-ATPases in rat brain synaptosomes. Caffeine and verapamil, two drugs known to affect calcium translocation, are very weak inhibitors of the Ca2+-ATPase. The Ki values for inhibition of the Ca2+-ATPase of rat and frog sarcoplasmic reticulum by PTX-B were comparable and ranged between 22 and 36 microM. Inhibition of calcium-dependent ATPase in sarcoplasmic reticulum by pumiliotoxin-B is noncompetitive with calcium and is not readily reversible. Based on structure-activity profiles, it is concluded that inhibition of Ca2+-ATPase by the indolizidine alkaloids is responsible for the alkaloid-elicited prolongation of twitch in intact muscle.
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PMID:Inhibition of calcium-dependent ATPase from sarcoplasmic reticulum by a new class of indolizidine alkaloids, pumiliotoxins A, B, and 251D. 645 30

The paper describes an investigation into the increase in intracellular free Ca2+ and resting tension of barnacle muscle fibers when exposed to CO2. Isometric tension was recorded in isolated myofibrillar bundles prepared from barnacles and crabs. On replacement of a low relaxing bathing solution (free Ca2+: 20 nM) at pH 7.1 with a similar one containing 100% CO2 and 13 mM HCO3-, also at pH 7.1, the bundles developed a phasic contraction, which aequorin experiments confirmed was due to a release of Ca2+ from a store within the bundles. The source of this Ca2+ is tentatively identified as the sarcoplasmic reticulum (SR) for the following reasons: (1) prior exposure to 20 mM caffeine depleted this Ca2+ store, (2) procaine (10 mM) inhibited the response, and (3) the extracellular space or "clefts" and the mitochondria could be eliminated as possible sources. An effect of the CO2 + HCO3- on the free Ca2+/Mg2+ ratio in the bathing solution was excluded as a possible mechanism. The diuretic furosemide (1 mM) enhanced the response to CO2 + HCO3-. Both furosemide and SITS (1--10 mM), by themselves, also released Ca2+ in myofibrillar bundles. A scheme is put forward to explain these results: it is suggested that diffusion of dissolved CO2 into the SR produces an acidification of the SR lumen, which modifies either the Ca2+/-ATPase or the Ca2+-induced release process in such a way to release Ca2+.
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PMID:Carbon dioxide or bicarbonate ions release Ca2+ from internal stores in crustacean myofibrillar bundles. 645 53

The lipophilic anion tetraphenylboron (TPB-) but not the lipophilic cation tetraphenylarsonium (TPA+) inhibited ATP-dependent Ca2+ accumulation by isolated sarcoplasmic reticulum. TPB- did not inhibit ATP hydrolysis but did induce Ca2+ release from preloaded vesicles. It did not appear to disrupt lipid bilayers or to act as a Ca2+ ionophore since it had no effect on the Ca2+ content of phospholipid vesicles. TPB- also induced Ca2+ release from sarcoplasmic reticulum in chemically skinned muscle fibers causing tension development. In contrast to other Ca2+-releasing agents such as caffeine, proton ionophores, or quercetin, the rise to peak tension was slow and tension was sustained, suggesting that Ca2+ release channels, once opened by TPB-, were held open as long as the compound was present in the membrane. Ca2+ uptake was re-established upon removal of TPB- or addition of TPA+. TPB- or TPA+ would probably distribute within the membrane, altering surface charges on both sides of the membrane. The fact that only a negatively charged ion brought about opening of Ca2+ release channels suggests that specific surface charges control Ca2+ release channels in sarcoplasmic reticulum. Although we have not been able to prove that TPB- acts exclusively on physiologically relevant Ca2+ release channels, we have shown that TPB- does not release Ca2+ from proteoliposomes reconstituted with the Ca2+ + Mg2+ ATPase. Thus TPB- does not induce Ca2+ release through channels formed by the ATPase molecule.
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PMID:Tetraphenylboron causes Ca2+ release in isolated sarcoplasmic reticulum and in skinned muscle fibers. 682 43

Plant cytokinesis appears to be a topographically organized process of exocytosis. Golgi vesicles which contain cell wall precursors are translocated during telophase, by interzonal microtubules, to the equatorial region of the mitotic apparatus where they fuse with each other giving rise to the new cell wall. Caffeine inhibits cytokinesis by hindering Golgi vesicle coalescence. The present results demonstrate that treatments which increase the cellular ATP level (adenosine, cycloheximide and anisomycin) counteract caffein-induced cytokinesis inhibition in meristem cells of onion root tips (Allium cepa L.), while treatments which decrease ATP level potentiate this caffeine effect (dinitrophenol, fluoroacetate, low oxygen tensions, etc.). We postulate that caffeine, in competition with the cellular ATP level, blocks cell plate formation by inhibiting a certain ATPase activity required for membrane fusion of Golgi vesicles.
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PMID:ATP level and caffeine efficiency on cytokinesis inhibition in plants. 711 65

I microinjected calcium ions into echinoderm eggs during mitosis to determine the calcium sensitivity of microtubules (Mts) in vivo. Spindle birefringence (BR), a measure of the number of aligned Mts in the spindle, is locally, rapidly, and reversibly abolished by small volumes of microinjected CaCl2 (1 mM). Rapid return of BR is followed by anaphase, and subsequent divisions are normal. Similar doses of MgCl2, BaCl2, KCl, NaCl, pH buffers, distilled water, or vegetable oil have no effect on spindle BR, whereas large doses of such agents sometimes cause slow, uniform loss in BR over the course of a minute or more. Of the ions tested, only Sr++ causes effects comparable to Ca++. Ca-EGTA buffers, containing greater than micromolar free Ca++, abolishes BR in a manner similar to millimolar concentrations of injected CaCl2. Caffeine, a potent uncoupler of the Ca++-pump/ATPase of sarcoplasmic reticulum, causes a local, transient depression in spindle BR in the injected region. Finally, injection of potassium oxalate results in the formation of small, highly BR crystals, presumably CA-oxalate, in Triton-sensitive compartments in the cytoplasm. Taken together, these findings demonstrate that spindle Mts are sensitive to levels of free Ca++ in the physiological range, provide evidence for the existence of a strong cytoplasmic Ca++-sequestering system, and support the notion that Mt assembly and disassembly in local regions of the spindle may be orchestrated by local changes in the cytoplasmic free Ca++ concentration during mitosis. An appendix offers the design of a new chamber for immobilizing echinoderm eggs for injection, a new method for determining the volume of the injected solution, and a description of the microinjection technique, which was designed, but never fully described, by Hiramoto (Y. Hiramoto, Exp. Cell. Res., 1962, 27:416-426.).
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PMID:Studies on the in vivo sensitivity of spindle microtubules to calcium ions and evidence for a vesicular calcium-sequestering system. 719 45

The molecular composition of intracellular Ca2+ stores in developing chicken cerebellum Purkinje neurons from embryonic day 11 (E11) to posthatching day 2 (P2) was studied by immunocytochemistry using specific antibodies for three molecular constituents, the receptor (R) and/or channel sensitive to inositol 1,4,5-trisphosphate (IP3), Ca(2+)-adenosinetriphosphatase (ATPase), and calsequestrin (CS). CS, IP3R, and Ca(2+)-ATPase were first detected by light-microscopic immunofluorescence in migrating Purkinje cells at E11-E12 and throughout late phases of embryonic development. Ontogenesis of CS, IP3R, and Ca(2+)-ATPase accompanied well-defined stages of cerebellum histogenesis and cytogenesis and was accomplished before hatching. High-resolution immunogold electronmicroscopy revealed that, at E18-P1, CS was still largely distributed to the endoplasmic reticulum (ER) lumen and began to be segregated to ER subcompartments (calciosomes) only by P2, whereas the IP3R was concentrated into ER cisternal stacks as early as E18. Both ionotropic and metabotropic plasma membrane receptors were present in dissociated single chicken Purkinje cells from E16 onward, as indicated by measurements of membrane currents (whole cell recording mode) and of cytoplasmic Ca2+ transients monitored with the cell-trappable fluorescent indicator fura 2-acetoxymethyl ester, respectively. Cytoplasmic Ca2+ transients were detected after either activation of glutamate metabotropic receptors, i.e., evidence of IP3-sensitive Ca2+ channels, or application of caffeine, i.e., evidence of ryanodine-sensitive Ca2+ channels. Intracellular Ca2+ stores appear to be functional during embryonic development.
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PMID:Intracellular Ca2+ stores in chick cerebellum Purkinje neurons: ontogenetic and functional studies. 749 12

1. The modulation of whole-cell K+ and Ca2+ currents by stimulation of histamine H1-receptors in freshly isolated single smooth muscle cells from the rabbit coronary artery was characterized using the patch-clamp technique at 35 degrees C. Single-channel K+ currents were also analysed using the cell-attached patch configuration. 2. The histamine H1-receptor agonist, 2-(2-aminoethyl)pyridine (AEP) (0.1 mM), increased the amplitude of voltage-activated inward Ba2+ currents, recorded using the perforated-patch recording technique, which could be completely blocked by the dihydropyridine antagonist, nicardipine (1 microM). 3. Whole-cell outward K+ currents in rabbit coronary artery cells could be classified into at least two components: (a) a slowly inactivating, 4-aminopyridine (4-AP)-sensitive low-noise current, and (b) a non-inactivating, tetraethylammonium (TEA)-sensitive high-noise current. 4. AEP (0.1 mM) caused changes in whole-cell outward K+ currents which depended upon membrane voltage. Specifically: (a) AEP enhanced the amplitude of outward currents at voltages between -30 and 0 mV, and (b) AEP decreased the outward currents at more positive potentials. 5. The removal of extracellular Ca2+ caused little inhibition of the effects of AEP on K+ currents, whereas the depletion of intracellular Ca2+ stores by pretreatment with ryanodine and caffeine prevented the effects of AEP on K+ channels. Moreover, acute exposure to ryanodine (10 microM) or thapsigargin (1 microM), a Ca(2+)-ATPase inhibitor, caused voltage-dependent changes in the outward currents similar to those observed with AEP. These results suggest that the voltage-dependent effects of AEP on K+ currents are mainly mediated by release of Ca2+ from intracellular stores. 6. The dual stimulatory and inhibitory effect of AEP on whole-cell K+ currents was shown to be due to a differential effect on two distinct types of K+ channels. The stimulatory effect observed over the voltage range -30 to 0 mV was prevented by pretreatment of cells with low concentrations of TEA (1 mM), whereas the inhibitory effect observed at positive potentials was prevented by pretreatment of cells with 4-AP (3 mM). 7. Single-channel recordings revealed two types of unitary K+ currents with conductances of 225 and 70 pS in the cell-attached configuration with symmetrical K+ solutions (150 mM K+ in pipette-150 mM K+ in bath). Bath application of AEP (0.1 mM) caused a marked increase in the open probability of the large conductance channels.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Modulation of K+ and Ca2+ channels by histamine H1-receptor stimulation in rabbit coronary artery cells. 750 29

Whether phosphatidylinositol hydrolysis and a subsequent Ca2+ mobilization are responsible for muscarine-induced transient outward currents (IO) and non-selective cation currents (INS) in the guinea-pig chromaffin cell was investigated using the perforated patch method. IO, but not INS, failed to be reproduced in Ca(2+)-free solution and was markedly reduced by prior exposure to caffeine under Ca(2+)-free conditions or by addition to normal solution of cyclopiazonic acid (CPA), a Ca2+ ATPase inhibitor. Application of CPA in Ca(2+)-free solution, however, suppressed INS by about 50% in 73% of the cells tested. Bath application of 1.5 mM neomycin, a phospholipase C inhibitor, induced the time-dependent decline of IO with near abolition at 20 min or less, whereas it produced a time-independent decrease of INS and an inwardly rectifying K+ current. INS in the presence or absence of neomycin was well fitted to rectangular hyperbolas with the same ED50 of 2.17 microM, but with a 33% smaller maximum amplitude in the former, indicating a non-competitive inhibition by neomycin. We conclude that, while phosphatidylinositol hydrolysis mediates the production of IO, it does not mediate that of INS by muscarine.
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PMID:Phosphatidylinositol hydrolysis is involved in production of Ca(2+)-dependent currents, but not non-selective cation currents, by muscarine in chromaffin cells. 754 Jan 39


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