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)

The Na(+)-K(+)-adenosine triphosphatase (Na(+)-K(+)-ATPase) activity and beta-endorphin immunoreactivity were determined in rat brain at the acute stage of ischemia produced by unilateral occlusion of the middle cerebral artery (MCA). The effect of pretreatment with naloxone on these activities was also evaluated in the same model. After MCA occlusion, Na(+)-K(+)-ATPase activity was promptly reduced in the ischemic hemisphere and remained at a lower level than in the contralateral hemisphere during 90 minutes of ischemia. A single intraperitoneal 0.5-mg injection of naloxone prior to MCA occlusion attenuated the inactivation. On the other hand, beta-endorphin immunoreactivity was significantly increased following ischemia. The increase was marked in the ischemic hemisphere and was also observed in the contralateral hemisphere; this increase was not affected by the administration of naloxone. These results indicate the possibility that naloxone contributes to protecting the brain from ischemia through stabilizing the cellular membrane. The possible mechanism by which naloxone attenuates the inactivation of Na(+)-K(+)-ATPase in the ischemic brain is discussed in view of alterations of the central beta-endorphin system during ischemia.
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PMID:Alterations in Na(+)-K(+)-ATPase activity and beta-endorphin content in acute ischemic brain with and without naloxone treatment. 215 61

The role of the Na/Ca exchanger in the control of cellular excitability and tension development is a subject of current interest in cardiac physiology. It has been suggested that this coupled transporter is responsible for rapid changes in intracellular calcium activity during single beats, generation of plateau currents, which control action potential duration, and control of intracellular sodium during Na/K pump suppression, which may occur during terminal states of ischemia. The actual behavior of this exchanger is likely to be complex for several reasons. First, the exchanger transports two ionic species and thus its instantaneous flux rate depends on both intracellular sodium and calcium activity. Secondly, the alteration in intracellular calcium activity, which is caused by a given transmembrane calcium flux, and which controls the subsequent exchanger rate, is a complex function of available intracellular calcium buffering. The buffers convert the ongoing transmembrane calcium fluxes into changes in activity that are a small and variable fraction of the change in total calcium concentration. Using a number of simple assumptions, we model changes in intracellular calcium and sodium concentration under the influence of Na/Ca exchange, Na/K ATPase and Ca-ATPase pumps, and passive sodium and calcium currents during periods of suppression and reactivation of the Na/K ATPase pump. The goal is to see whether and to what extent general notions of the role of the Na/Ca exchanger used in planning and interpreting experimental studies are consistent with its function as derived from current mechanistic assumptions about the exchanger. We find, for example, that based on even very high estimates of intracellular calcium buffering, it is unlikely that Na/Ca exchange alone can control intracellular sodium during prolonged Na/K pump blockade. It is also shown that Na/Ca exchange can contaminate measurements of Na/K pump currents under a variety of experimental conditions. The way in which these and other functions are affected by the dissociation constants and total capacity of the intracellular calcium buffers are also explored in detail.
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PMID:Interaction of intracellular ion buffering with transmembrane-coupled ion transport. 215 93

Ischemia-reperfusion heart cell injury may be mediated, at least in part, through the generation of oxy radicals. Therefore, mechanisms of action of two oxidants on a membrane model, partially purified Na,K,ATPase, were investigated. Effects of H2O2, an oxygen intermediate postulated to play a primary role in reperfusion injury, on the function of the enzyme were time-dependent and potentiated by Fe ions. The inhibition of enzyme activity was prevented by chelators, but not by hydroxyl radical scavengers. The results support the view that the possible mode of enzyme modification involves H2O2-derived, Fe ion-catalyzed, localized ("site-specific") hydroxyl radical formation. The action of hypochlorous acid (HOCl), a powerful oxidant postulated to be produced by activated neutrophils, was quantitatively similar to that of H2O2 plus Fe ions in causing enzyme dysfunction. This is partly because relatively large doses of oxidants were required, due to the presence of physiological anti-oxidant defense mechanisms in the membrane. Although a combination of deferoxamine (Fe ion chelator) and dithiothreitol (DTT) (sulfhydryl reducing agent) was most effective in preventing the enzyme modification, once enzyme inactivation by oxidants is in progress, deferoxamine plus DTT could only arrest further deterioration of the enzyme function. Therefore, the oxidant-induced change in membrane dysfunction advances with time; the advance can be stalled, but the enzyme activity cannot be restored to normal.
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PMID:Effect of oxidants on Na,K,ATPase and its reversal. 217 45

Na,K-ATPase concentration was measured by vanadate facilitated 3H-ouabain binding to intact samples taken from various parts of porcine and canine myocardium. In porcine and canine heart 3H-ouabain binding site concentration in ventricles was 1.4-2.5 times larger than in atria. Evaluation of 3H-ouabain binding kinetics revealed no major difference between atria and ventricles: Equilibrium was obtained after the same incubation time in right atrium (RA) as in left ventricle (LV), both in porcine and canine heart. Unspecific uptake and retention of 3H-ouabain was for porcine heart RA and LV 1.5 and 1.4, respectively, and for canine heart RA and LV, both 1.2% filling (i.e., volume (ml) of incubation medium 3H-radioactivity taken up per mass unit (g wet wt.) of tissue multiplied by 100). The apparent dissociation constant (KD) was 1.4 x 10(-8) and 1.9 x 10(-8) in porcine RA and LV and 2.6 x 10(-8) and 6.1 x 10(-8) mol/l in canine RA and LV. Loss of specifically bound 3H-ouabain during the washout procedure occurred with a half-life time (T1/2) of 16.7 and 28.6 in RA and LV of porcine heart and 91.2 and 151.6 h in RA and LV of canine heart. Duly corrected for these errors of the method--factor 1.16 and 1.13, respectively, for porcine RA and LV, and factor 1.11 and 1.13 for canine RA and LV, total 3H-ouabain binding site concentration was found to be 553 +/- 74 and 1037 +/- 45 pmol/g wet wt. (means +/- SEM, n = 5) in porcine RA and LV, and 569 +/- 37 and 1410 +/- 40 pmol/g wet wt. (means +/- SEM, n = 5) in the canine RA and LV. These values were confirmed by measurements of 3H-digoxin binding to the porcine heart. The present quantification of myocardial Na,K-ATPase gives values up to 154 times higher than measurements based upon Na,K-ATPase activities in membrane fractions where the recovery of Na,K-ATPase may be less than 1% due to loss during purification. A higher Na,K-ATPase concentration is found in small animals than in large animals. A relationship between higher concentration of Na,K-ATPase and larger pressure work in ventricles compared to atria is suggested. Myocardial 3H-ouabain binding sites were found to be stable for 20 min of ischemia, followed by 1 h of reperfusion, supporting the concept that myocyte injury induced by short term ischemia may be reversible and that reperfusion may result in normalization.
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PMID:Quantification of the total Na,K-ATPase concentration in atria and ventricles from mammalian species by measuring 3H-ouabain binding to intact myocardial samples. Stability to short term ischemia reperfusion. 217 46

Unilateral ischemia in the right cerebral hemisphere of the rat was induced by ligation of the right common carotid artery coupled with controlled hemorrhage to produce hypotension (25 +/- 8 mm/Hg). Where indicated after 30 min of ischemia, the withdrawn blood was reinfused to restore arterial pressure to normal. Mitochondria isolated from the ipsilateral hemisphere after 30 min of ischemia showed significantly lower respiratory rates than the organelles isolated from the contralateral side. Oxidation of NAD(+)-linked substrates was more sensitive to inhibition in ischemia (30%) than was of ferrocytochrome c (12%), succinate oxidation being intermediate. The activities of membrane-bound dehydrogenases (both NADH and succinate-linked) were also significantly lowered. Ischemia did not affect the cytochrome content of mitochondria. Respiratory activity (NAD(+)-linked) of mitochondria isolated from the ipsilateral hemisphere was twice as sensitive to inhibition by fatty acid as was of preparations from the contralateral side. Mitochondria isolated from cerebral cortex after 90 min of post-ischemic reperfusion showed no significant improvement in the rate of substrate oxidation. Adenine nucleotide translocase activity and energy-dependent Ca2+ uptake, both of which decreased significantly in mitochondria isolated from the ischemic brain, showed little recovery, on reperfusion. These observations suggested the strong possibility that the deleterious effects of ischemia on mitochondrial respiratory function might be mediated by free fatty acids that are known to accumulate in large amounts in ischemic tissues. The pattern of inhibition of ATPase activity was consistent with this view.
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PMID:Influence of cerebral ischemia and post-ischemic reperfusion on mitochondrial oxidative phosphorylation. 234 84

The purpose of this study was to explore the relationship between the extent of sarcolemmal damage observed 2 h after reperfusion of myocardium which had been ischemic for either 0.5 or 1 h and the long-term recovery of function of that same myocardium. For this purpose we studied the Ca2+ pumping ATPase activity and protein phosphorylation of sarcolemmal vesicles isolated after 2 h reperfusion. Both activities declined depending on the duration of ischemia, which suggests the development of sarcolemmal Ca2+ pump failure. Morphological examination of the sarcolemma by thin-section and freeze-fracture electronmicroscopy, in biopsies obtained after 2 h of reperfusion, showed severe clustering of intramembranous particles and formation and extrusion of lipidic liposomal structures which also depended on the duration of ischemia. Except for the occurrence of minor particle aggregation in the samples which had been ischemic for 0.5 h, sarcolemmal disruption was only seen in those myocardial segments which had been subjected to 1 h of coronary artery ligation. Recovery of regional myocardial function, assessed by 2-D-echocardiography after 2 weeks of reperfusion, was closely related to the degree to which sarcolemmal integrity was maintained after 2 h reperfusion.
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PMID:Loss of functional and structural integrity of the sarcolemma: an early indicator of irreversible injury of myocardium? 244 91

The effects of different periods of myocardial ischemia on sarcoplasmatic reticulum function were studied in porcine hearts in which successive occlusions of branches of the left anterior descending coronary artery yielded myocardium ischemic for 0.5, 1 or 2 h. Sarcoplasmatic reticulum vesicles were isolated from transmural biopsies of control and ischemic segments. Ca2+ pumping ATPase was already impaired after 0.5 h of ischemia (77 +/- 9% of control, n = 5) and had decreased to 44 +/- 9% of control (n = 4) after 1 h of ischemia. The functional damage caused by ischemia may be related to an altered second messenger control of the Ca2+ pump because the in vitro phosphorylation of phospholamban by catalytic subunit was also reduced.
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PMID:Sarcoplasmatic reticulum function in the ischemic myocardium. 244 93

The voltage- and time-dependent slow channels in the myocardial cell membrane are the major pathway by which Ca2+ ions enter the cell during excitation for initiation and regulation of the force of contraction of cardiac muscle. These slow channels appear to behave kinetically, on a population basis, as if their gates open, close, and recover more slowly than those of the fast Na+ channels. In addition, the slow channel gates operate over a less negative (more depolarized) voltage range. Tetrodotoxin does not block the slow channels, whereas the calcium antagonistic drugs, Mn2+, Co2+, and La3+ ions do. The slow channels have some special properties, including functional dependence on metabolic energy, selective blockade by acidosis, and regulation by the intracellular cyclic nucleotide levels. Because of these special properties of the slow channels, Ca2+ influx into the myocardial cell can be controlled by extrinsic factors (such as autonomic nerve stimulation or circulating hormones) and by intrinsic factors (such as cellular pH or ATP level). During transient regional ischemia, the selective blockade of the slow channels, which results in depression of the contraction and work of the afflicted cells, might protect the cells against irreversible damage by helping to conserve their ATP content. Reperfusion arrhythmias may be caused by the breakdown of this protective mechanism, in that, upon reperfusion, the Ca2+ slow channels may recover before the cells are capable of handling the greater Ca2+ influx (Fig. 20). As depicted in this figure, the Ca2+ slow channels may recover their function before the ATP level is sufficiently recovered to allow bail-out of the intracellular Ca2+. In addition, the generation of free radicals upon reperfusion may injure the Ca-ATPase and other enzymes involved in Ca2+ metabolism. The net effect of this would be to cause Ca2+ overload of the cells and SR, with subsequent delayed after-depolarizations (DADs) leading to triggered automaticity and arrhythmias. Following blockade of the fast Na+ channels in myocardial cells with TTX or by voltage-inactivating them in 25 mM (K)0, catecholamines, angiotensin-II, histamine, and methylxanthines rapidly allow the production of slowly-rising Ca2+-dependent action potentials by increasing the number of Ca2+ slow channels available for voltage activation and/or their mean open time. Concomitantly, these compounds rapidly elevate intracellular cyclic AMP levels, suggesting that cyclic AMP is somehow related to the functioning of the slow channels. Exogenous cyclic AMP produces the same effect, but much more slowly.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Regulation of calcium slow channels of cardiac muscle by cyclic nucleotides and phosphorylation. 245 7

Total renal ischemia for various time intervals (0-50 min) resulted in the rapid and duration-dependent redistribution of polarized membrane lipids and proteins in renal proximal tubule cells. Following only 15 min of ischemia, apical membrane enrichment of NaK-ATPase, normally a basolateral membrane (BLM) enzyme, had increased (1.6 +/- 0.6 vs. 2.9 +/- 1.2, P less than 0.01). In vivo histochemical localization of NaK-ATPase showed reaction product throughout the apical microvillar region. PTH-stimulatable adenylate cyclase, another BLM protein, was also found in ischemic but not control apical membrane fractions. One dimensional SDS-PAGE showed four bands, present in control BLM and ischemic apical membranes, which could not be found in control apical membrane fractions. Immunohistochemical localization of leucine aminopeptidase (LAP) showed the enzyme was limited to the apical domain in control cells. Following ischemic injury (50 min), LAP staining could be seen within the cell and along the BLM. Following 24 hr of reperfusion, the BLM distribution of LAP was further enhanced. With cellular recovery from ischemic injury (5 days), LAP was again only visualized in the apical membrane. Duration-dependent alterations in apical and BLM lipids were also observed. Apical sphingomyelin and phosphatidylserine and the cholesterol-to-phospholipid ratio decreased rapidly while apical phosphatidylcholine and phosphatidylinositol increased. Taken together, these results indicate renal ischemia causes rapid duration-dependent reversible loss of surface membrane polarity in proximal tubule cells.
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PMID:Characterization of ischemia-induced loss of epithelial polarity. 246 76

We hypothesize that enhanced activity of capillary Na,K-ATPase promotes Na+ influx into the brain and causes early edema formation in focal cerebral ischemia. The pharmacologic suppression of brain capillary Na,K-ATPase as a means to ameliorate edema formation was examined using the middle cerebral artery occlusion model in 36 cats. With the help of a catheter inserted into the middle cerebral artery, the ischemic brain area was directly perfused with 10(-5) M ouabain. Perfusion was maintained as intermittent 15-second pulse injections given every 5 (n = 6) or 2 (n = 6) minutes. By this method, the naturally occurring circulatory conditions during ischemia were not altered. Four hours after ischemia, the cortical specific gravity at each of six locations over the ischemic area was compared with the corresponding ischemic blood flow measured by the H2 clearance technique. The results show that ouabain perfused every 2 minutes significantly ameliorated edema formation compared with six control cats perfused with Krebs-Ringer solution. In a separate series of experiments, the Na+ flux across the blood-brain barrier was studied by injecting 22NaCl together with an intravascular reference (cobalt-57-labeled microspheres 15 microns in diameter) into the ischemic area. The brain uptake index of 22Na was markedly increased in the ischemic cortex of six control cats; ouabain treatment in six cats suppressed the increase of Na+ influx. The results support our hypothesis that brain capillary Na,K-ATPase activity increases during early focal ischemia, leading to enhanced Na+ together with H2O flux across the blood-brain barrier.
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PMID:Effect of enhanced capillary activity on the blood-brain barrier during focal cerebral ischemia in cats. 247 24


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