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)

Urinary acidification by the turtle bladder is due to a H+-ATPase that is located in the luminal membrane. The rate of H+ transport is stimulated by an increase in the ambient CO2. Using the fluorescent dye acridine orange, we showed that the mitochondria-rich cell of this equilibrium contains vesicles whose internal pH is acidic. We measured the pH of these vesicles by using endocytosed fluorescein isothiocyanate-labeled dextran and found it to be near 5.0. The pH increased after treatment with protonophores or metabolic inhibitors, suggesting that it was due to a H+ pump rather than to a Donnan effect. In bladders preloaded with fluorescent dextran, CO2 stimulated exocytosis and H+ transport measured simultaneously in the same bladder. The increase in the H+ current correlated well with the extent of exocytosis, and both were inhibited by pretreatment with colchicine. We conclude that the turtle bladder contains an intracellular reserve of vesicles containing H+ pumps and CO2 stimulates rapid fusion of these vesicles with the luminal membrane with consequent insertion of H+ pumps, thereby stimulating H+ secretion across the whole epithelium.
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PMID:Exocytosis regulates urinary acidification in turtle bladder by rapid insertion of H+ pumps into the luminal membrane. 628

Digitalis sensitivity of the heart is increased in patients with ischemic heart disease. Whether this elevation of digitalis sensitivity occurs as the result of ischemia-induced changes in the cardiac tissue and whether changes in the sarcolemmal Na,K-adenosine triphosphatase (ATPase) or reserve capacity of the sodium pump are responsible for the increased digitalis sensitivity were examined using isolated heart preparations obtained from guinea pigs. Ligation of the left anterior descending coronary artery (LAD) in Langendorff preparations 40 min before perfusion with a toxic concentration (either 1.8 or 2.5 microM) of digoxin decreased the time to the onset of arrhythmias. LAD-ligation by itself did not cause arrhythmias. The time to the onset of arrhythmias during digoxin perfusion was slightly longer in preparations obtained from reserpine-treated animals; however, the reserpine pretreatment failed to alter the effect of LAD ligation on digitalis sensitivity, indicating that the release of catecholamines is not involved in the sensitization. The effects of ischemia on Na,K-ATPase and sodium pump activities, glycoside binding to the enzyme and reserve capacity of the sodium pump were examined in globally ischemic Langendorff preparations. The preparations were perfused with a Krebs-Henseleit bicarbonate buffer solution (pH 7.4) saturated with a 95% O2-5% CO2 gas mixture at a control flow rate of 2.5 ml/g of tissue per min or at 5 or 0% of the control flow rate. After 6 hr of zero perfusion, Na,K-ATPase activity and the number of specific ouabain binding sites were reduced in ventricular muscle homogenates. However, the remaining Na,K-ATPase was not altered in its sensitivity to dihydrodigoxin-induced inhibition or affinity of binding sites for ouabain, sodium or potassium. Similar results were observed after reperfusion following 2 or 5 hr of zero perfusion. A 5% perfusion for 2 or 6 hr, or zero perfusion for 2 hr failed to affect Na,K-ATPase activity in muscle homogenates. Sodium pump activity in ventricular slices, estimated from the ouabain-sensitive 86Rb+ uptake, was unchanged after 5% perfusion or zero perfusion for 2 hr, but was significantly reduced after a 20-min reperfusion following 2 hr of zero perfusion. Reserve capacity of the sodium pump, as estimated from the differences in 42K+ uptake by right ventricular strips under 1.5 and 7 Hz stimulation, was unaffected by 2 hr of 5% perfusion. These results indicate that coronary artery occlusion enhances the arrhythmogenic action of digitalis in isolated heart preparations. This change in digitalis sensitivity produced by 40 min of occlusion cannot be explained by reductions in Na,K-ATPase activity or sodium pump reserve capacity as 2 hr of zero perfusion does not alter Na,K-ATPase or sodium pump activity in ventricular tissue.
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PMID:Ischemia-induced enhancement of digitalis sensitivity in isolated guinea-pig heart. 630 6

The effect of changing [K+], [Na+] and [Cl-] in nutrient solution was studied in bullfrog antrum with and without HCO3- in nutrient. In 25 mM HCO3- (95% O2/5% CO2) and in zero HCO3- (100% O2), nutrient pH was maintained at 7.3. Changing from 4 to 40 mM K+ or from 81 to 8.1 mM Cl- gave a decrease 10 min later in transmucosal PD (nutrient became more negative)--a normal response. These responses were less in zero than in 25 mM HCO3-. A decrease from 102 to 8 mM Na+ decreased PD (anomalous response of electrogenic NaCl symport). This effect was attenuated or eliminated in zero HCO3-. In contrast, change from 4 to 40 mM K+ gave initial anomalous PD response and change from 102 to 8 mM Na+, initial normal PD response with either zero or 25 mM HCO3-. Both responses were associated with (Na+ + K+)-ATPase pump and were greater in zero than in 25 mM HCO3-. Initial PD increases in zero HCO3- are explained as due to increase in the resistance of passive conductance and/or NaCl symport pathways. Thus, removal of HCO3- modifies conductance pathways of nutrient membrane.
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PMID:Potential difference responses due to K+, Na+ and Cl- changes in bullfrog antrum with and without HCO3-. 631 19

Membrane vesicles were purified from resting corpus mucosa of pig stomachs by velocity-sedimentation on a sucrose-Ficoll step gradient. Two vesicular fractions containing the (H+ + K+)-ATPase were obtained. One fraction was tight towards KCl, the other was leaky. At 21 degrees C maximal (H+ + K+)-ATPase activities of 0.8 and 0.4 mumol X mg-1 X min-1, respectively, were observed in lyophilized vesicles. The vesicles contained a membrane-associated carbonic anhydrase, the activity of which was in 100-fold excess of the maximal ATPase activity. Both vesicular fractions were rich in phosphatidylcholine, phosphatidylethanolamine, sphingomyelin and cholesterol. The characteristics of ion permeability and transport in the tight vesicles were in agreement with corresponding data for vesicles of a tubulovesicular origin in the parietal cell. Measurement of the rate of K+ uptake into the vesicles was based on the ability of K+ to promote H+ transport. The uptake was slow and dependent on the type of anion present. The effectiveness in promoting uptake of K+ by anions was SCN- greater than NO3- greater than Cl- much greater than HCO3- greater than SO4(2-). Uptake of K+ was much more rapid at alkaline pH than at neutral or at acidic pH. Addition of CO2 at alkaline pH strongly stimulated the rate of H+ accumulation in the vesicles. The initial part of this stimulation was sensitive to acetazolamide, an inhibitor of carbonic anhydrase. A model how the (H+ + K+)-ATPase and the carbonic anhydrase may co-operate is presented. It is concluded that membrane vesicles of a tubulovesicular origin can produce acid.
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PMID:Characterization of proton-transporting membranes from resting pig gastric mucosa. 631 22

The effects of K+, Na+ and ATP on the gastric (H+ + K+)-ATPase were investigated at various pH. The enzyme was phosphorylated by ATP with a pseudo-first-order rate constant of 3650 min-1 at pH 7.4. This rate constant increased to a maximal value of about 7900 min-1 when pH was decreased to 6.0. Alkalinization decreased the rate constant. At pH 8.0 it was 1290 min-1. Additions of 5 mM K+ or Na+, did not change the rate constant at acidic pH, while at neutral or alkaline pH a decrease was observed. Dephosphorylation of phosphoenzyme in lyophilized vesicles was dependent on K+, but not on Na+. Alkaline pH increased the rate of dephosphorylation. K+ stimulated the ATPase and p-nitrophenylphosphatase activities. At high concentrations K+ was inhibitory. Below pH 7.0 Na+ had little or no effect on the ATPase and p-nitrophenylphosphatase, while at alkaline pH, Na+ inhibited both activities. The effect of extravesicular pH on transport of H+ was investigated. At pH 6.5 the apparent Km for ATP was 2.7 microM and increased little when K+ was added extravesicularly. At pH 7.5, millimolar concentrations of K+ increased the apparent Km for ATP. Extravesicular K+ and Na+ inhibited the transport of H+. The inhibition was strongest at alkaline pH and only slight at neutral or acidic pH, suggesting a competition between the alkali metal ions and hydrogen ions at a common binding site on the cytoplasmic side of the membrane. Two H+-producing reactions as possible candidates as physiological regulators of (H+ + K+)-ATPase were investigated. Firstly, the hydrolysis of ATP per se, and secondly, the hydration of CO2 and the subsequent formation of H+ and HCO3-. The amount of hydrogen ions formed in the ATPase reaction was highest at alkaline pH. The H+/ATP ratio was about 1 at pH 8.0. When CO2 was added to the reaction medium there was no change in the rate of hydrogen ion transport at pH 7.0, but at pH 8.0 the rate increased 4-times upon the addition of 0.4 mM CO2. The results indicate a possible co-operation in the production of acid between the H+ + K+-ATPase and a carbonic anhydrase associated with the vesicular membrane.
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PMID:Effects of pH on the interaction of ligands with the (H+ + K+)-ATPase purified from pig gastric mucosa. 631 23

Effect of changing [K+], [Na+] and [Cl-] in nutrient solution on potential difference (PD) and resistance was studied in bullfrog antrum with and without nutrient HCO3(-) but with 95% O2/5% CO2 in both cases. In both cases, changing from 4 to 40 mM K+ gave about the same initial PD maximum (anomalous response) which was followed by a decrease below control level. Latter effect was much less with zero than with 25 mM HCO3(-). Changing from 102 to 8 mM Na+ gave initial normal PD response about the same in both cases. However, 10 min later the change in PD with zero HCO3(-) was insignificant but with 25 mM HCO3(-) the PD decreased (anomalous response of electrogenic NaCl symport). PD maxima due to K+ and Na+ were largely related to (Na+ + K+)-ATPase pump. Changes in nutrient Cl- from 81 to 8.1 mM gave only a decrease in PD (normal response). Initial PD increases are explained by relative increases in resistance of simple conductance pathways and of parallel pathways of (Na+ + K+)-ATPase pump and Na+/Cl- symport. Removal of HCO3(-) and concurrent reduction of pH modify resistance of these pathways.
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PMID:Effect of reduced pH in absence of HCO3(-) on anomalous and normal potential responses in bullfrog antrum. 632 82

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

Rat heart mitochondria oxidizing pyruvate (in the presence of 20% as much malate) took up nearly the amount of oxygen required for complete oxidation to CO2. Thus pyruvate, a physiological substrate of the citrate cycle, is oxidized through the entire cycle in these mitochondria, and they seem suitable for study of regulation of integrated mitochondrial energy transduction. By addition of graded amounts of hexokinase or pyruvate kinase to the suspending medium (in the presence of excess glucose or phosphoenolpyruvate), a wide range of steady-state values of the ATP/ADP concentration ratio was obtained. At a constant concentration of phosphate, the steady-state rate of oxygen uptake by rat heart mitochondria oxidizing pyruvate was a function of the adenylate energy charge or of the ATP/ADP ratio, and relatively independent of the absolute concentrations of these nucleotides. The oxygen uptake rates typically spanned a range of about 20-fold. At very high values of the ATP/ADP ratio, the rate of oxygen uptake is much lower than the "state 4" rate seen after added ADP has been phosphorylated. This result suggests that "state 4" respiration, at least in these freshly prepared mitochondria, measures the rate at which ADP is made available by ATPase activity, rather than indicating uncoupling of electron transport from phosphorylation. The concentration of orthophosphate affected the rate of oxygen uptake and the pattern of response to the ATP/ADP ratio or the energy charge, but the effects did not seem interpretable in terms of the mass-action expression for hydrolysis of ATP, (ATP)/ (ADP) (Pi).
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PMID:Adenine nucleotide control of the rate of oxygen uptake by rat heart mitochondria over a 15- to 20-fold range. 671 43

Recent in vitro studies from the rat and rabbit have suggested a tightly coupled sodium/hydrogen ion exchanger on the luminal membrane of proximal tubules. The steep sodium gradient from the lumen to cell supplies indirect energy for hydrogen ions to be pumped from the cell to the lumen. However, a proton translocating pump has been demonstrated in other epithelia, which is independent of sodium transport and directly driven by ATP. To examine the role that sodium might play in the process of acidification, rat proximal convoluted tubules and their surrounding peritubular capillaries were perfused in vivo with artificial ultrafiltrate-like perfusion solutions. Total CO2 absorption was measured by microcalorimetry during alterations in sodium transport by replacement of the sodium with an impermeant cation, choline, or by inhibition of the (Na+ + K+)-ATPase by removing potassium from both perfusion solutions. Under control conditions the absolute rate of total CO2 absorption was 140 pmol/mm X min. In the choline substitution and potassium removal experiments, absolute total CO2 absorption fell to 23 and 28 pmol/mm X min, respectively. The data suggest that: 1) in the rat superficial proximal convoluted tubule approximately 80% of the bicarbonate absorption is tightly coupled to sodium transport; 2) this process is driven indirectly by the (Na+ + K+)-ATPase system; and 3) the residual 20% of acidification appears to be mediated by another mechanism or may be a consequence of technical limitations.
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PMID:Evidence for coupled sodium/hydrogen exchange in the rat superficial proximal convoluted tubule. 681 17

The effects of infusions of ouabain on chemoreceptor activity recorded from the peripheral end of a sectioned carotid sinus nerve were studied in cats anaesthetized with pentobarbitone. Ouabain caused a marked increase in chemoreceptor discharge followed by a decline in discharge to frequencies near or below the pre-ouabain level; during the latter period further administration of ouabain had no effect. Infusion of ouabain during hypoxia further increased the chemoreceptor discharge, but this effect was short-lasting. On intracarotid administration ouabain was less effective in cats with the ganglioglomerular (sympathetic) nerves cut, whereas on intravenous administration no significant difference was observed. Following intravenous administration of ouabain the chemoreceptor peak discharge occurred with dose levels similar to those needed to cause cardiac arrhythmias, but following intracarotid administration the chemoreceptor discharge peaked at doses about 40% of those causing arrhythmias. During ouabain-induced excitation the stimulatory action of NaCN, CO2-equilibrated Locke solution and acetylcholine was potentiated, as was the chemo-inhibition induced by dopamine. During the post-excitatory period the responses evoked by these substances were reduced or abolished. Neither mecamylamine, a nicotinic antagonist, nor physostigmine, an anti-cholinesterase, affected the response of the carotid chemoreceptors to ouabain. The major finding of this study was that ouabain initially 'sensitizes' the carotid body chemoreceptors and then 'desensitizes' them. The most likely mechanism responsible for these effects is the well established Na+--K+-ATPase-inhibiting property of ouabain.
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PMID:Effects of ouabain on carotid body chemoreceptor activity in the cat. 687 75


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