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)

We have recently demonstrated that K(+)-induced dilation of cerebral resistance-sized vessels has two independent components, only one of which seemed sodium pump dependent. In our current investigation, potassium-induced dilation of spontaneous tone was compared in cerebral arteries from normotensive Wistar-Kyoto rats and age-matched stroke-prone spontaneously hypertensive rats. Branches of the posterior cerebral artery were cannulated and pressurized, and these vessels developed spontaneous tone. After a 5-minute period in K(+)-free physiological saline solution, K+ was increased in 1-mM increments to a final concentration of 15 mM. In the normotensive arteries, K+ concentrations between 0 and 5 mM K+ resulted in dilations that had a transient (sodium pump-dependent) component, and K+ concentrations in excess of 7 mM produced dilations that lacked a transient (sodium pump-independent) component. Similar branches from the hypertensive rat also responded with transient dilations to K+ (less than 5 mM), and these were significantly greater at 3 mM K+. However, the maintained dilations to K+ (greater than 7 mM), noted in preparations from Wistar-Kyoto rats, were absent in seven of eight preparations. Thus, the impaired dilations, in the hypertensive vessels, to K+ described here is a consequence of altered function of some sodium pump-independent component rather than altered Na+,K(+)-ATPase activity.
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PMID:Impaired potassium-induced dilation in hypertensive rat cerebral arteries does not reflect altered Na+,K(+)-ATPase dilation. 217 51

The response of sodium, potassium-adenosine triphosphatase (Na,K-ATPase) to cyclic adenosine monophosphate (cAMP)-dependent protein kinase was examined in membranes obtained from rabbit iris-ciliary body. In the presence of the protein kinase together with 10(-5) M cAMP, Na,K-ATPase activity was reduced. No change in Na,K-ATPase activity was detected in response to the protein kinase without added cAMP. Likewise cAMP alone did not alter Na,K-ATPase activity. Reduction of Na,K-ATPase activity was also observed in the presence of the cAMP-dependent protein kinase catalytic subunit. The response of the enzyme to the kinase catalytic subunit was also examined in membranes obtained from rabbit ciliary processes. In the presence of 8 micrograms/ml of the catalytic subunit, ciliary process Na,K-ATPase activity was reduced by more than 50%. To examine whether other ATPases were suppressed by the protein kinase, calcium-stimulated ATPase activity was examined; its activity was stimulated by the catalytic subunit. To test whether the response of the ciliary process Na,K-ATPase is unique, experiments were also performed using membrane preparations from rabbit lens epithelium or rabbit kidney; the catalytic subunit significantly reduced the activity of Na,K-ATPase from the kidney but not the lens. These Na,K-ATPase studies suggest that in the iris-ciliary body, cAMP may alter sodium pump activity. In parallel 86Rb uptake studies, we observed that ouabain-inhibitable potassium uptake by intact pieces of iris-ciliary body was reduced by exogenous dibutryl cAMP or by forskolin.
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PMID:Alteration of sodium, potassium-adenosine triphosphatase activity in rabbit ciliary processes by cyclic adenosine monophosphate-dependent protein kinase. 217 Feb 91

The aim of the present work was to evaluate the action of cyclosporin (CsA) both in vivo and in vitro on the active sodium transport across the erythrocyte membrane of rheumatoid arthritis (RA) patients. The in vivo study was performed on 20 patients affected by refractory RA and treated with CsA (5 mg/kg/die) or with azathioprine (2 mg/kg/die) before and after 7 days' therapy. The control group was formed of 25 healthy subjects. RA patients before treatment showed increased intra-erythrocyte Na+ concentration and decreased Na+, K+ ATPase activity in comparison with normal subjects. A rise in the activity of the sodium pump and a reduction in the intra-erythrocyte Na+ concentration were observed after cyclosporin treatment, but not after azathioprine. The in vitro study was performed on intact RBCs and on erythrocyte membranes from 15 healthy subjects and from 12 patients affected by classical RA, in the presence or absence of CsA (0.5-1-2 micrograms/ml). CsA (0.5 micrograms/ml) increased the Na+, K+ ATPase activity in intact RBCs and in erythrocyte membranes from both groups of subjects. Intracellular Na+ was decreased only in erythrocytes from RA patients after addition of 0.5 micrograms/ml CsA. A direct action of CsA on the membrane hydrophobic environment of the Na+, K+ ATPase is hypothesized on the basis of the present results.
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PMID:Cyclosporin effect on sodium and potassium transport across erythrocytes in rheumatoid arthritis. 217 Nov 39

Isolated myocytes of rat heart, and sealed sarcolemmal vesicles of bovine heart, were used to examine the selectivity of the effects of partially reduced oxygen species (generated by a mixture of xanthine and xanthine oxidase) on cardiac sodium pump and several other ion transporters of the plasma membrane. When myocytes were exposed to xanthine plus xanthine oxidase, there were time-dependent inhibitions of ouabain-sensitive 86Rb+ uptake and (Na+ + K+)-ATPase activity that could be prevented by allopurinol, or by catalase and superoxide dismutase; suggesting the involvements of H2O2 or oxygen free radicals in the inhibition of the pump. This inhibition preceded any significant decrease in cellular ATP or in the number of viable cells. While ouabain increased 45Ca2+ uptake by myocytes as expected, exposure to xanthine plus xanthine oxidase decreased 45Ca2+ uptake; suggesting that the Na+, Ca2(+)-exchanger of the intact myocytes is also inhibited by oxygen metabolites. Simultaneous inhibitions of the pump, the Na+, Ca2(+)-exchange, the Na+, H(+)-exchange, and the Na+, Pi-cotransport activities also occurred in sarcolemmal vesicles that were treated with xanthine plus xanthine oxidase. These findings indicate that inactivations of the sodium pump and other sarcolemmal ion carriers are early events in the oxidant-induced damage to the cardiomyocyte. In the rat heart myocytes, a fraction of (Na+ + K+)-ATPase that seems to be more sensitive to ouabain, was inactivated more rapidly upon exposure of myocytes to xanthine plus xanthine oxidase; raising the possibility of the existence of different pump populations with different sensitivities to extracellularly generated oxygen metabolites.
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PMID:Studies on the specificity of the effects of oxygen metabolites on cardiac sodium pump. 217 59

The presence of an endogenous ouabain-like substance in bovine hypothalamus is demonstrated on the bas is of the ability of acid acetone extracts of hypothalamus to inhibit (NA+ + K+)-ATPase activity, 86Rb uptake, 22Na efflux and (3H)ouabain binding. Partial purification of the substance was achieved by acetic acid fractionation followed by sephadex-G25 chromatography and subsequent desalting by mixed-bed resin. The results are discussed with relation to the important role of the sodium pump inhibitor in the regulation of (N+ + K+)-ATPase activity and sodium transport and hence in the pathophysiologic mechanisms of essential hypertension.
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PMID:[(NA++K+)-ATPase inhibitor from bovine hypothalamus]. 217 83

Today it is accepted that estrogens mitigate the consequences of ischemic heart disease. Preliminary experiments revealed an increase in heart sarcolemmal (Na+ + K+)-ATPase activity after application of estradiol in vivo. It is also well known the key role of latter enzyme for heart function. The facts mentioned above indicate that estradiol may act on the heart just via modulation of the (Na+ + K+)-ATPase activity. In present paper it is confirmed that 17-beta-estradiol stimulates the activity of sarcolemmal (Na+ + K+)-ATPase by allosteric manner, particularly by increasing positive cooperativity between the K(+)-binding sites of the enzyme. This effect is manifested by enhancement in functional capacity of the sodium pump in sarcolemma. Stimulatory effect of estradiol is bound to integrated myocytes: neither is it manifested in isolated sarcolemma in vitro nor exhibits any influence on the affinity of binding sites for cardiac glycosides or on total capacity of the sarcolemma to bind ouabain. Basing on the data obtained it was assumed that estradiol acts on the (Na+ + K+)-ATPase not directly but by means of a mediator released within the myocyte.
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PMID:Mechanism of action of estradiol on sodium pump in sarcolemma from the myocardium. 217 17

Endogenous factors cross-reacting with antidigoxin antibodies have been found in several tissues and body fluids of animals and humans, using commercially available digoxin radioimmunoassay or enzyme immunoassay methods. The chemical characteristics of these endogenous factors are, at present, unknown, although it has been suggested that they could be substances with low molecular weight. Experimental studies and theoretical considerations indicate that endogenous digitalis-like factors (DDLFs), in addition to the ability to react with antibodies, might also bind to the specific cellular receptor of the cardiac glycosides and thus inhibit the membrane Na+/K(+)-ATPase (sodium pump). Therefore, EDLF can be an endogenous modulator of the membrane sodium-potassium pump and several authors have suggested that EDLF could play a role in the regulation of fluids and electrolytes, muscular tone of myocardial and also in the pathogenesis of arterial hypertension. In this review, the authors discuss the hypothesis that, in metabolic diseases such as diabetes mellitus, obesity and acromegaly, the sodium retention and volume expansion, possibly due to exaggerated sodium intake, and/or exogenously induced peripheral hyperinsulinemia and high levels of growth hormone, could trigger a sustained release of EDLF, which in turn increases the blood pressure.
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PMID:Is the endogenous digitalis-like factor the link between hypertension and metabolic disorders as diabetes mellitus, obesity and acromegaly? 222 23

The steroid nature of the cardiac glycosides (CG) suggests that an endogenous steroid (or steroids) may be the natural ligand for the specific receptor site, i.e., Na+,K+-ATPase. Derivatives of progesterone (PROG) that compete in a [3H]ouabain radioreceptor binding assay (RRA) are characterized by 17 alpha-acetylation and modifications in the B ring. Chlormadinone acetate (CMA) is the most potent analog identified thus far, having about one-twentieth the RRA potency of ouabain. CMA interacts at the ouabain site on Na+,K+-ATPase, inhibits the enzyme in the same rank order of species sensitivity as do the CG, and inhibits the sodium pump in vitro in guinea pig atrium and perfused heart, cardiac myocytes, rat diaphragm, and red blood cells. CMA does not cross-react with digoxin antiserum, which indicates that CG antibodies are not necessarily directed at molecular determinants of biological activity. By crystallographic analysis, the 20-carbonyl moiety in CMA is seen spatially oriented so as to be equivalent to the lactone 23-oxygen atom in the CG. CMA exerts primarily cardiodepressant effects, in accordance with the often-reported similar action of PROG. Negative inotropy may be mediated other than by Na+,K+-ATPase because PROG itself has no significant CG-like actions. Positive inotropy by CG, cardiodepression by CMA and PROG or low concentrations of CG, occasional transient enhancement of contractility by CMA, and pump stimulation by low concentrations of CMA or CG may reflect different affinities of the compounds for sites that mediate Na+,K+-ATPase/pump inhibition, positive inotropy, and negative inotropy. Thus, PROG derivatives related to CMA appear to be likely candidates for endogenous digitalis-like hormones. Body tissues possess the enzymes for conversion of PROG to derivatives related even more closely than the semisynthetic CMA to the CG configuration.
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PMID:Progesterone derivatives that bind to the digitalis receptor: effects on Na+,K+-ATPase and isolated tissues. 241 7

The direct effects of amiloride on myocardial contractility were examined in electrically stimulated left atrial muscle of guinea-pig heart. Amiloride (0.3 to 1.5 mM) produced a positive inotropic effect which, at higher concentrations, was followed by a decline in developed tension. These effects were not accompanied by contracture or arrhythmia and were not affected by a combination of phentolamine, nadolol, cimetidine, tripelennamine and atropine. The above concentrations of amiloride prolonged the action potential duration during the development of the positive inotropic effect; however, no further change in the action potential duration was observed during the decline in developed tension caused by high concentrations of amiloride. Myocardial membrane Na,K-ATPase, ouabain-sensitive 86Rb+ uptake and Na+-dependent Ca2+ efflux from sarcolemmal membrane vesicles were all inhibited by amiloride. The positive inotropic effect of the agent is reduced and the negative inotropic action is enhanced in low Na+ solutions, i.e., under conditions likely to favor Ca2+ influx via Na+/Ca2+ exchange. These results suggest that amiloride, under the present conditions, has a complex interaction with cardiac muscle fibers. Amiloride may produce its inotropic effects in guinea-pig atrial muscle by several mechanisms including sodium pump inhibition, Na+/Ca2+ exchange inhibition, prolongation of the action potential duration, and/or actions such as Na+/H+ exchange inhibition which were not directly addressed in this study.
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PMID:Amiloride: effects on myocardial force of contraction, sodium pump and Na+/Ca2+ exchange. 242 Sep 97

The possibility that H+ might substitute for Na+ at Na+ sites of Na+,K+-ATPase was studied. Na+,K+-ATPase purified from pig kidney showed ouabain-sensitive K+-dependent ATPase activity in the absence of Na+ at acid pH (H+,K+-ATPase). The specific activity was 1.1 mumol Pi/mg/min at pH 5.7, whereas the specific activity of Na+,K+-ATPase was 14 mumol Pi/mg/min at pH 7.5. The enzyme was phosphorylated from ATP in the absence of Na+ at the acid pH. The initial rate of the phosphorylation was also accelerated at the acid pH in the absence of Na+, and the maximal rate obtained at pH 5.5 without Na+ was 9% of the rate at pH 7.0 with Na+. The phosphoenzyme was sensitive to K+ but almost insensitive to ADP. The phosphoenzyme was sensitive to hydroxylamine treatment and the alpha-subunit of the enzyme was found to be phosphorylated. H+,K+-ATPase was inhibited as effectively as Na+,K+-ATPase by N-ethylmaleimide but was less inhibited by oligomycin or dimethyl sulfoxide. These results indicate that protons have an Na+-like effect on the Na+ sites of Na+,K+-ATPase and suggest that protons can be transported by the sodium pump in place of Na+.
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PMID:Proton transport catalyzed by the sodium pump. Ouabain-sensitive ATPase activity and the phosphorylation of Na,K-ATPase in the absence of sodium ions. 242 57


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