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)

Despite previous reports [McLaughlin (1985) Mol. Biochem. Parasitol. 15, 189-201; Ghosh, Ray, Sarkar and Bhaduri (1990) J. Biol. Chem. 265, 11345-11351; Mazumder, Mukherjee, Ghosh, Ray and Bhaduri (1992) J. Biol. Chem. 267, 18440-18446] that the plasma membrane of different trypanosomatids only contains Ca(2+)-ATPase that does not show any demonstrable dependence on Mg2+, a high-affinity (Ca(2+)-Mg2+)-ATPase was demonstrated in the plasma membrane of Trypanosoma brucei. The enzyme became saturated with micromolar amounts of Ca2+, reaching a Vmax. of 3.45 +/- 0.66 nmol of ATP/min per mg of protein. The Km,app. for Ca2+ was 0.52 +/- 0.03 microM. This was decreased to 0.23 +/- 0.05 microM, and the Vmax. was increased to 6.36 +/- 0.22 nmol of ATP/min per mg of protein (about 85%), when calmodulin was present. T. brucei plasma-membrane vesicles accumulated Ca2+ on addition of ATP only when Mg2+ was present, and released it to addition of the Ca2+ ionophore A23187. In addition, this Ca2+ transport was stimulated by calmodulin. Addition of NaCl to Ca(2+)-loaded T. brucei plasma-membrane vesicles did not result in Ca2+ release, thus suggesting the absence of a Na+/Ca2+ exchanger in these parasites. Therefore the (Ca(2+)-Mg2+)-ATPase would be the only mechanism so far described that is responsible for the long-term fine tuning of the intracellular Ca2+ concentration of these parasites. The trypanocidal drug pentamidine inhibited the T. brucei plasma-membrane (Ca(2+)-Mg2+)-ATPase and Ca2+ transport at concentrations that had no effect on the Ca(2+)-ATPase activity of human or pig erythrocytes. In this latter case, pentamidine behaved as a weak calmodulin antagonist, since it inhibited the stimulation of the erythrocyte Ca(2+)-ATPase by calmodulin.
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PMID:A calmodulin-stimulated Ca2+ pump in plasma-membrane vesicles from Trypanosoma brucei; selective inhibition by pentamidine. 828 74

The retinal pigment epithelium (RPE) lying between the neural retina and the choroid, performs as a transport organ for solutes and water between the choriocapillaries and the subretinal space. It also has the function to maintain the microenvironment of photoreceptors including the regulation of calcium ions during light or dark adaptation. In order to further elucidate the transport functions of the RPE, apical membranes were isolated from RPE by differential precipitation with divalent ions. In this work bovine tissues were used as well as elasmobranch tissues. For the latter, we have already purified and characterized membrane vesicles in a previous paper. Na(+)-K(+)-ATPase, alkaline phosphatase, and 5'-nucleotidase, which are marker enzymes of the apical membrane, were highly enriched in the final membrane fraction. The majority of the fraction consists of right side out vesicles. The fluorescent indicator for sodium, SBFI, or the calcium specific indicator, Fura-2, were pre-loaded into the apical membrane vesicles of RPE of either dogfish eyes or bovine eyes. When an outwardly-directed Ca2+ gradient was formed across the vesicular membranes, the Ca2+ influx was also enhanced by 136% for dogfish RPE and 167% for bovine RPE. This Na+ gradient dependent Ca2+ influx was blocked by bepridil, an antiarrhythmic agent which is a Na+/Ca2+ exchanger inhibitor. These results indicate that a Na+/Ca2+ exchanger is present in the apical membrane of bovine and dogfish RPE.
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PMID:A Na+/Ca2+ exchange mechanism in apical membrane vesicles of the retinal pigment epithelium. 848 15

In chromaffin granule ghosts, the Na+/Ca2+ exchanger in the granule membrane can provide a high affinity (Km 1-3 microM) and high capacity (Vmax 50-100 nmol mg min-2) mechanism for Ca2+ accumulation. The activity of the Na+/H+ antiporter can be used to couple Ca2+ uptake via Na+/Ca2+ exchange to ATP-dependent proton translocation via the granule membrane H(+)-ATPase. Therefore, Ca2+ uptake can be indirectly linked to the proton pump. However, under conditions designed to mimic the environment of a granule in the cytosol of a chromaffin cell, measured rates of Ca2+ uptake are low, a free Ca2+ concentration of about 5 microM in the ghost matrix being attained. Under such circumstances, the granules seem unlikely to play a major role in calcium homeostasis in the intact cell.
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PMID:Indirect coupling of calcium transport in chromaffin granule ghosts to the proton pump. 851 42

In heart failure alterations of intracellular Ca2+ handling are thought to be a major reason for impaired contraction and relaxation. Peak Ca2+ transients are reduced, resting Ca2+ levels elevated, and the time course of diastolic Ca2+ decline is markedly prolonged in failing hearts. The proteins of the sarcoplasmic reticulum and the sarcolemmal Na+/Ca2+ exchanger are the most important tools for Ca2+ homeostasis in the cardiomyocyte, and their molecular cloning has allowed prediction of structure/function analysis. The investigation of function and gene expression of these proteins in failing myocardium has been an area of intensive research in recent years in order to provide a more detailed understanding of the pathophysiology of heart failure. Quantitative changes in expression of the sarcoplasmic reticulum Ca(2+)-ATPase, the ryanodine receptor, and the Na+/Ca2+ exchanger with correlations to functional alterations have been reported both in experimental animal models and in the human failing heart. However, in human heart failure these findings are currently the subject of a lively discussion because observations have apparently been in part contradictory. This review discusses the proteins involved in myocardial Ca2+ handling and describes the current state of research on expressional and functional alterations and their potential implication in the pathomechanism of heart failure.
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PMID:Calcium transport proteins in the nonfailing and failing heart: gene expression and function. 858 10

The subcellular distribution of the calmodulin-stimulated plasma-membrane Ca(2+)-ATPase (PMCA) has been studied in rat and rabbit skeletal muscle cells by indirect (calmodulin gel overlays) and direct (Western blotting with specific antibodies) methods. It has also been studied in situ in immunocytochemistry experiments. The distribution of PMCA has been compared with that of the NA+/Ca2+ exchanger and of the dihydropyridine receptor, which has been studied by Western blotting with specific antibodies. Both PMCA and the Na+/Ca2+ exchanger had a dual localization, i.e., they were found in the plasma membrane and in the transverse-tubule fractions of the two main types of skeletal muscles studied. The pump and the exchanger were not diffusely distributed in the transverse-tubule-membrane system, but specifically confined to the membrane domain where the dihydropyridine receptor was also localized, i.e., the junctional membrane. Experiments with isoform-specific antibodies have shown that the pump isoform expressed in skeletal muscle is PMCA 1.
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PMID:Colocalization of the dihydropyridine receptor, the plasma-membrane calcium ATPase isoform 1 and the sodium/calcium exchanger to the junctional-membrane domain of transverse tubules of rabbit skeletal muscle. 864 89

Gentamicin nephrotoxicity may arise in part from alterations in the expression of genes critical for renal proximal tubule metabolism. We tested the hypothesis that gentamicin suppressed the gene expression of the Na+/Ca2+ exchanger (NaCaX), glucose transporter 1 (GLUT1) and alpha 1-subunit of Na(+)-K(+)-ATPase (alpha 1-NKA) in renal tubules. The products of these genes mediate Na(+)-dependent Ca2+ efflux, glucose efflux and influx, and ATP-dependent Na+ efflux across tubular basolateral membranes, respectively. After 10 days of gentamicin intoxication (40 mg/kg ip, twice daily), levels of mRNAs encoding NaCaX and the cognate protein declined. GLUT1 mRNA levels increased, although GLUT1 protein levels were also reduced. Moreover, whereas alpha 1-NKA mRNA levels remained unchanged, alpha 1-NKA protein levels were also reduced. We suggest that the higher GLUT1 mRNA level is part of the stress response to tubular injury. However, regardless of the mRNA level, the most consistent effect of gentamicin was reduction of specific protein levels. We propose that failure to translate high levels of mRNA into proportionally high levels of protein, as in the case of GLUT1, may attenuate the expression of stress response gene products, and thus diminish the possibility of recovery in gentamicin intoxication.
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PMID:Studies of renal injury. I. Gentamicin toxicity and expression of basolateral transporters. 877 84

In principal cells of rat cortical collecting ducts (CCD) the K+ conductance of the basolateral membrane is functionally coupled to the Na(+)-K(+)-ATPase. Inhibition of the Na(+)-K(+)-ATPase by ouabain resulted in a decrease of this conductance. This inhibition was absent in the presence of amiloride. In the present study we attempted to measure the activities of intracellular Na+ ([Na+]i) and intracellular Ca2+ ([Ca2+]i) fluorimetrically, and discuss their role for the functional coupling of the activity of the Na(+)-K+ pump and the recently identified K+ channels in the basolateral membrane [Na+]i and [Ca2+]i were measured in isolated CCD segments using the Na(+)-sensitive dye sodium-binding benzofuran isophthalate (SBFi) and the Ca2+-sensitive dye fura-2 as fluorescence indicators. Basal [Na+]i and [Ca2+]i were 22 +/- 4 mM (n = 23) and 84 +/- 13 nM (n = 28), respectively. With amiloride (10 microM) [Na+]i and [Ca2+]i decreased by 5 +/-1 mM (n = 18) and by 19 +/- 9 nM (n = 21), respectively. With ouabain (0.5 mM), [Na+]i and [Ca2+]i increased by 30 +/- 7 mM (n = 7) and by 25 +/- 10 nM (n = 13), respectively. In the presence of amiloride, ouabain increased [Na+]i by only 8 +/- 3 mM (n = 7), while [Ca2+]i did not change significantly (delta = -2 + 3 nM, n = 13). The observed parallel changes in [Ca2+]i and [Na+]i are compatible with the function of the Na+/Ca2+ exchanger present in the basolateral membrane of the CCD. The K+ channels in the basolateral membrane of rat CCD are inhibited by increases in [Ca2+]i. These These data suggest the changes in [Na+]i and consecutive changes in [Ca2]i as possible functional link between the K+ conductance of the basolateral membrane and the Na(+)-K(+)-ATPase of rat CCD.
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PMID:Correlation between intracellular activities of Ca2+ and Na+ in rat cortical collecting duct--A possible coupling mechanism between Na+-K+-ATPase and Basolateral K+ conductance. 881 14

In the present study, we have investigated the mechanism of affinity modulation of alpha IIb beta 3 by chymotrypsin. We first confirmed that alpha-chymotrypsin could activate alpha IIb beta 3 (approximately 7,000 molecules per platelet) without major intracellular signaling. However, we unexpectedly found that high concentrations of amiloride dose-dependently inhibited 125I-fibrinogen binding to the chymotrypsin-treated platelets, as well as the platelet aggregation (IC50 [50% inhibitory concentration] for fibrinogen binding, 530 mumol/L). In contrast, amiloride did not inhibit alpha IIb beta 3 activation induced by anti-alpha IIb beta 3 monoclonal antibody PT25-2 or AP5. To identify the pathway involved, the effects of alteration of Na+ gradient in platelets were examined. Lowering Na+ gradient by replacing extracellular Na+ with tetramethylammonium (TMA) increased the number of activated alpha IIb beta 3 by twofold, as assessed by fibrinogen-binding assay. The incubation of platelets with ouabain, a Na+/K(+)-adenosine triphosphatase (ATPase) inhibitor, further augmented alpha IIb beta 3 activation. These data suggested that a likely candidate for the pathway was Na+/Ca2+ exchanger. At 140 mmol/L [Na+]o, 45Ca2+ influx to the chymotrypsin-treated platelets was twofold greater than that to non-treated platelets. Replacement of Na+ with TMA further increased the Ca2+ influx, and the increase was inhibited by amiloride dose-dependently. 3',4'-Dichlorobenzamil (DCB) and bepridil, relatively specific inhibitors of Na+/Ca2+ exchanger, also inhibited the chymotrypsin-induced alpha IIb beta 3 activation, and the IC50 values of these inhibitors for fibrinogen binding were 25 mumol/L and 52 mumol/L, respectively. Moreover, platelet aggregation induced by various physiologic agonists was inhibited by DCB or bepridil, while platelet agglutination by ristocetin was not. Our data newly suggest that Na+/Ca2+ exchanger operating in reverse mode may be directly involved in inside-out signaling that activates alpha IIb beta 3.
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PMID:Affinity modulation of the platelet integrin alpha IIb beta 3 by alpha-chymotrypsin: a possible role for Na+/Ca2+ exchanger. 883 52

Renal distal convoluted tubules (DCT) are a major site of hormone-regulated, active calcium absorption. Calcium exit across basolateral plasma membranes is thought to be mediated by Na+/Ca2+ exchange and a Ca(2+)-ATPase. In this report the presence and function of Na+/Ca2+ exchangers in DCT cells were assessed. cDNAs encoding a conserved region and the variable regions of three alternatively spliced isoforms of the Na+/Ca2+ exchanger, NACA2, NACA3, and NACA6, were isolated in a ratio of 7:12:1 using homology-based reverse transcription-polymerase chain reaction (RT-PCR) with RNA from an immortalized mouse DCT cell line. Northern blots probed with a 32P-labeled PCR product from a conserved region of the exchanger were positive for a single transcript of 7 kb in primary cultures of distal tubule cells (cortical ascending limb + DCT cells), consistent with the reported size of the exchanger in other tissues. Na+/Ca2+ exchange was assessed by measuring sodium-dependent changes of intracellular calcium ([Ca2+]i), in single cells. In the presence of an outward Na+ gradient, [Ca2+]i increased by 240%. Collapsing the Na+ gradient with monensin inhibited the rise of [Ca2+]i. Removal of extracellular Ca2+ or the addition of an Na+ ionophore inhibited the rise of [Ca2+]i. The intracellular Na+ concentration decreased upon removal of extracellular Na+ in parallel with the rise of [Ca2+]i. Western analysis performed on membranes prepared from DCT cells or primary cultures of distal tubule cells with a polyclonal antibody revealed bands at approximately 125 and 85 kDa, consistent with reported sizes for exchanger protein. These findings show that Na+/Ca2+ exchanger transcripts, protein, and activity are present in DCT cells and that Na(+)-dependent Ca2+ efflux may be mediated by NACA2, NACA3, and NACA6.
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PMID:Structural and functional analysis of Na+/Ca2+ exchange in distal convoluted tubule cells. 885 17

The cardiac Na+ pump (Na+ -K+ -ATPase) provides the driving force for the Na+/Ca2+ exchanger, a determinant of intracellular Ca2+ stores. Three Na+ pump alpha-catalytic subunit isoforms are expressed in human heart, alpha1 and alpha2 are expressed in rat heart, and only alpha1 is expressed in guinea pig heart. The objective of this study was to determine whether there are isoform-specific patterns of expression in the transverse tubules (T tubules) vs. the peripheral sarcolemma. In adult rat cardiomyocytes, anti-alpha1-specific antibodies labeled the T tubules more intensely than the peripheral sarcolemma, in which labeling was patchy, the same pattern reported for distribution of the Na+/Ca2+ exchanger (J. S. Frank, G. Mottino, D. Reid, R. S. Molday, and K. D. Philipson, J. Cell Biol. 117: 337-345, 1992), whereas anti-alpha2- and anti-beta1-antibodies uniformly labeled T tubules and peripheral sarcolemma. In guinea pig cardiomyocytes, an anti-alpha-antibody against an extracellular epitope evenly labeled the peripheral sarcolemma and T tubules, and immunogold labeling demonstrated coincidence of alpha-subunits and intramembranous particles in sarcolemma. In summary, Na+ pumps are located in both peripheral sarcolemma and T tubules of cardiomyocytes expressing either multiple or single Na+ pump isoforms.
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PMID:Subcellular distribution of sodium pump isoform subunits in mammalian cardiac myocytes. 892 49


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