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)

An open circuit kinetic model was developed to calculate the time course of proximal tubule cell pH, solute concentrations, and volume in response to induced perturbations in luminal or peritubular fluid composition. Solute fluxes were calculated from electrokinetic equations containing terms for known carrier saturabilities, allosteric dependences, and ion coupling ratios. Apical and basolateral membrane potentials were determined iteratively from the requirements of cell electroneutrality and equal opposing transcellular and paracellular currents. The model converged to membrane potentials accurate to 0.05% in one to four iterations. Model variables included cell concentrations of Na, K, HCO3, glucose, pH (uniform CO2), volume, and apical and basolateral membrane potentials. The basic model contained passive apical membrane transport of Na/H, Na/glucose, H and K, basolateral transport of Na/3HCO3, K, H, and glucose, and paracellular transport of Na, K, Cl, and HCO3; apical H and basolateral 3Na/2K-ATPases were present. Apical Na/H and basolateral K transport were regulated allosterically by pH. Apical Na/H transport, basolateral Na/3HCO3 transport, and the 3Na/2K-ATPase were saturable. Model parameters were chosen from data in the rat proximal tubule. Model predictions for the magnitude and time course of cell pH, Na, and membrane potential in response to rapid changes in apical and peritubular Na and HCO3 were in excellent agreement with experiment. In addition, the model requires that there exist an apical H-ATPase, basolateral Na/3HCO3 transport saturable with HCO3, and electroneutral basolateral K transport.
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PMID:Kinetic transport model for cellular regulation of pH and solute concentration in the renal proximal tubule. 358 Apr 82

The relationships between pHi (intracellular pH) and phosphate compounds were evaluated by nuclear magnetic resonance (NMR) in normo-, hypo-, and hypercapnia, obtained by changing fractional inspired concentration of CO2 in dogs anesthetized with 0.75% isoflurane and 66% N2O. Phosphocreatine (PCr) fell by 2.02 mM and Pi (inorganic phosphate) rose by 1.92 mM due to pHi shift from 7.10 to 6.83 during hypercapnia. The stoichiometric coefficient was 1.05 (r2 = 0.78) on log PCr/Cr against pHi, showing minimum change of ADP/ATP and equilibrium of creatine kinase in the pH range of 6.7 to 7.25. [ADP] varied from 21.6 +/- 4.1 microM in control (pHi = 7.10) to 26.8 +/- 6.3 microM in hypercapnia (pHi = 6.83) and 24.0 +/- 6.8 microM in hypocapnia (pHi = 7.17). ATP/ADP X Pi decreased from 66.4 +/- 17.1 mM-1 during normocapnia to 25.8 +/- 6.3 mM-1 in hypercapnia. The ADP values are near the in vitro Km; thus ADP is the main controller. The velocity of oxidative metabolism (V) in relation to its maximum (Vmax) as calculated by a steady-state Michaelis-Menten formulation is approximately 50% in normocapnia. In acidosis (pH 6.7) and alkalosis (pH 7.25), V/Vmax is 10% higher than the normocapnic brain. This increase of V/Vmax is required to maintain cellular homeostasis of energy metabolism in the face of either inhibition at extremes of pH or higher ATPase activity.
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PMID:Relationship between intracellular pH and energy metabolism in dog brain as measured by 31P-NMR. 359 78

The precise mechanisms by which the mammalian kidney proximal tubule transports H+ and HCO3- and regulates cytosolic pH (pHi) remain in doubt, though both a H+-ATPase pump and Na+/H+ exchange at the luminal membrane are known to function in the export of protons. The mechanisms of HCO3- transport are less clear though recent reports suggest an important role for an electrogenic Na+/HCO3- symport in the basolateral membrane. The importance of chloride-dependent bicarbonate transport is unknown. In the present studies, the pH-sensitive fluorescent dye, bis-(carboxyethyl)-carboxyfluorescein (BCECF) has been used to study pHi changes in suspensions of canine proximal tubule cells following acidification or alkalinization of the cytosol. Cells were acid-loaded to pH 6.5 by exposure to the H+/K+ ionophore, nigericin. Following removal of nigericin, pHi returned to basal levels (pHi = 7.1) when the cells were resuspended in a buffer containing 100 mM Na+. This recovery was blocked by removal of Na+ or addition of 0.2 mM amiloride to the cell suspension. In the presence of 0.2 mM amiloride and Na+, partial excretion of the acid load occurred if the buffer also contained HCO3-/CO2, but this effect was blocked by the removal of Na+ or the addition of 1 mM 4-acetomido-4'-isothiocyano-2,2'-stilbene disulfonic acid (SITS). When cell membrane potential was monitored in these experiments using the potential-sensitive fluorescent dye, bis-(1,3-dibutylbarbiturate) trimethine oxonol, the increase in pHi seen in the presence of Na+ was found to be electroneutral, whereas when that occurred in the presence of Na+, amiloride and HCO3-/CO2 was associated with membrane hyperpolarization.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cytoplasmic pH regulation in canine renal proximal tubule cells. 359 51

Isolated guinea pig distal colons secreted acid into the mucosal bathing solution at a rate of 1.0-1.5 mumol X cm-2 X h-1 when the preparations were mounted in Ussing chambers and bathed with HCO3(-)-CO2-free solution. The rates of the acidification and alkalinization of the solutions were measured by a pH stat system or calculated from changes in the pH of the solution. The acid secretion was localized in the middle and distal parts of the colon but absent in the proximal part of the colon and the cecum. The mucosal acidification was accompanied by serosal alkalinization, the rate of the latter being approximately 60% of the former. A carbonic anhydrase inhibitor, methazolamide (10(-4) M), reduced both the mucosal acidification and serosal alkalinization rates by a similar magnitude. The mucosal acidification was completely abolished by mucosal K+-free conditions but unaffected by mucosal Na+-free conditions. Ouabain added to the mucosal solution promptly inhibited the acid secretion. Dose dependency of the inhibition conformed to the Michaelis-Menten equation with a half-maximal effect at 4 X 10(-6) M. When the pH of the mucosal solution was reduced to 4.3, the rate of the mucosal acidification remained essentially the same as that at pH = 7.4. Vanadate (10(-4) M) added to both the mucosal and serosal solutions significantly reduced the mucosal acidification rate. These results suggest that CO2 derived from the epithelial metabolism is hydrated by carbonic anhydrase in the cell and released H+ enters the mucosal solution while HCO3- enters the serosal solution. H+ exit across the mucosal membrane may be mediated by H+-ATPase that is sensitive to ouabain.
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PMID:Acid secretion in isolated guinea pig colon. 365 23

The present investigation was undertaken to clarify the in vitro effect of zinc on bone metabolism in tissue culture. Calvaria were removed from weanling rats (3-week-old males) and cultured for periods up to 96 hr in Dulbecco's Modified Eagle Medium (high glucose, 4500 mg/dl) supplemented with antibiotics and bovine serum albumin. The experimental cultures contained 10(-7) to 10(-3) M zinc sulfate. All cultures were incubated at 37 degrees in 5% CO2/95% air. Zinc uptake by bone was increased significantly in cultures with concentrations of zinc greater than 10(-6) M. Bone calcium content was increased significantly by the presence of 10(-4) M zinc. This increase was blocked by the presence of 10(-6) M cycloheximide. Bone alkaline phosphatase activity was elevated in the presence of zinc (10(-6) to 10(-3) M), but the effect was inhibited by 10(-7) M cycloheximide or 10(-8) M actinomycin D. Zinc (10(-4) M) also significantly increased ATPase activity in the bone, whereas it did not alter significantly by pyrophosphatase, acid phosphatase and beta-N-acetylglucosaminidase activities. Furthermore, bone collagen content was raised by 10(-6) to 10(-4) M zinc. This elevation was prevented by 10(-7) cycloheximide or 10(-8) M actinomycin D. Bone DNA content and [3H]thymidine incorporation by the bone were not altered significantly by 10(-4) M zinc. These findings indicate that the zinc had a direct stimulatory effect on bone mineralization in vitro, and that bone protein synthesis was a necessary component of this response. Zinc may stimulate bone formation in tissue culture.
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PMID:Stimulatory effect of zinc on bone formation in tissue culture. 368 32

Net hepatic Ca2+ efflux, K+ uptake and glycogen breakdown in response to the alpha 1-adrenergic agonist phenylephrine were studied. Rat livers were perfused with CO2/bicarbonate-buffered solutions containing 10 microM Ca2+ and different amounts of Mg2+. K+-free medium and/or ouabain were used to block (Na+ + K+)-ATPase-dependent K+ uptake. In some experiments a sharp increase in extracellular Ca2+ concentrations was produced by infusing CaCl2 into the medium entering the liver. Perfusion with K+-free medium and ouabain enhanced the phenylephrine-induced Ca2+ efflux and diminished the glycogenolytic response, indicating a dissociation of Ca2+ release and glycogenolysis. Exogenous Ca2+ had practically no effect if livers were perfused with regular medium containing 1.2 mM Mg2+. In the presence of phenylephrine and if extracellular Mg2+ concentrations were lowered by omitting Mg2+ from the medium or by preperfusion with EGTA, exogenous Ca2+ was glycogenolytically effective and also produced a transient K+ uptake. Increased extracellular concentrations of Mg2+ inhibited the effects of exogenous Ca2+. In the presence of phenylephrine, higher concentrations of Mg2+ were needed than in the absence of alpha 1-adrenergic agonist to achieve a similar degree of inhibition. In one respect ouabain effects were comparable to those of phenylephrine: the glycoside also increased the metabolic response to exogenous Ca2+ and diminished the sensitivity towards Mg2+. Phenylephrine and ouabain may both enhance the permeability of plasma membranes for Ca2+.
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PMID:The hepatic response to Ca2+ is inhibited by Mg2+ and enhanced by phenylephrine or ouabain. 391 85

Three different isoenzymes of human carbonic anhydrase are now well characterized. Carbonic anhydrase I and II have been known for several years and are located in high amounts in red blood cells as well as in many other tissues. Carbonic anhydrase III, a protein showing CO2 hydratase and p-nitrophenylphosphatase activity was isolated from skeletal muscle some years ago. Earlier observations based on enzyme activity and radioimmunoassay studies have suggested that this protein is present in greater quantities in red skeletal muscles than in white ones. We have purified CA III from human soleus muscle and using obtained monospecific polyclonal antibody localized this protein in the same muscle fibers which show acid resistant ATPase activity. Using this protein as a marker for type I muscle fibers, fiber classification into type I and II could now be done also from paraffin embedded sections.
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PMID:Purification and localization of human carbonic anhydrase. III. Typing of skeletal muscle fibers in paraffin embedded sections. 393 Apr 40

Transport systems involved in proximal tubule HCO-3 reabsorption were examined in disaggregated renal cortical tubules from rabbits with metabolic alkalosis. The acid-base disorder was induced by first treating the animals with furosemide, and then maintaining them on low Cl--high HCO-3 diets. On this regimen, the rabbits had increases in blood pH and total CO2 values and decreases in serum K+ concentrations. Urine Cl- concentrations were less than 15 mEq/L in all cases. Na+-H+ exchange was evaluated by incubating tubules in rotenone in an Na+-free medium to deplete them of Na+ and adenosine triphosphate. Then the tubules were resuspended in media containing 65 or 12.5 mEq/L Na+ at either pH 7.1 or pH 7.6. The rise in cell pH estimated by dimethadione distribution was taken as a measure of Na+-H+ exchanger activity. At the high incubation pH, Na+-H+ exchanger activity appeared to be the same in tubules taken from alkalotic rabbits compared with those prepared from normal rabbits. At the low incubation pH, the activity of this transport system appeared to be depressed by 40% to 50% in alkalosis, with kinetics that suggested a decreased Vmax for the exchanger. Na+-independent H+ transport, presumably reflecting activity of an H+-adenosine triphosphatase, was evaluated by preincubating tubules in a Na+-free medium in the presence of ouabain, and then sequentially exposing them to and removing them from a solution containing 20 mmol/L NH4Cl.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Proximal tubule hydrogen ion transport processes in diuretic-induced metabolic alkalosis. 400 20

To examine the possible contribution of active H+ secretion mediated by brush border enzymes to proximal tubule HCO-3 absorption, paired reperfusions of surface proximal convoluted tubules were performed with the inhibitor dicyclohexylcarbodiimide (DCCD). In control studies using a solution devoid of HCO-3 but containing 5.5 mM glucose, 1 mM DCCD had no effect on glucose or fluid (Na+) absorption, suggesting that this inhibitor did not interfere with sodium entry at the brush border or mitochondrial energy production (ATP synthesis). In experiments using a perfusion solution containing 18-25 mM HCO-3, DCCD caused a fall in absolute CO2 absorption of approximately 15% under eucapneic conditions and 30% during acute hypercapnia. One millimole per liter amiloride (an inhibitor of the passive Na+-H+ exchanger) caused a 15% inhibition of CO2 absorption during acute hypercapnia and a disproportionately large reduction in fluid (Na+) absorption. The latter was not due to cell poisoning, since 1 mM amiloride had no inhibitory effect on fluid or glucose absorption when a HCO-3-free perfusion solution was used. Addition of 1 mM DCCD to a perfusion solution containing either 10(-3) M amiloride or 10(-4) M acetazolamide caused a significant inhibition of CO2 absorption compared with amiloride or acetazolamide alone. The observations are consistent with the view that in addition to passive Na+-H+ exchange, active transport mediated by either a H+-ATPase or a redox-driven H+ pump in the brush border contributes significantly to HCO-3 absorption in the proximal tubule.
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PMID:Evidence for a DCCD-sensitive component of proximal bicarbonate reabsorption. 406 52

The monovalent cationic ionophores monensin and nigericin stimulated rapid guinea pig sperm acrosome reactions in the presence of extracellular Na+, Ca2+ and bicarbonate (HCO3-/CO2). Extracellular K+ (mM concentrations), in contrast, was not required for the stimulatory effect of the ionophores. The effect of HCO3-/CO2 is concentration, pH and temperature dependent, with maximal responses obtained with 50 microM monensin or 25 microM nigericin at a concentration of 30 mM HCO3-, 2.5% CO2 and pH 7.8 at 25 degrees C. At a constant HCO3- concentration (30 mM), monensin stimulated acrosome reactions within the pH range 7.5-7.8, whereas a higher or lower pH did not support acrosome reactions at 25 degrees C. At constant extracellular pH (7.8), monensin stimulated acrosome reactions in the presence of 30 mM HCO3-, whereas higher and lower concentrations did not support acrosome reactions at 25 degrees C. The permeant anions pyruvate and lactate were essential to maintain sperm motility when treated with monensin under these conditions. NH4Cl, sodium acetate and 4,41-diisothiocyano-2, 21-disulfonic acid stibene (DIDS; 25 microM), an anion transport inhibitor, blocked the ability of monensin to stimulate acrosome reactions. Verapamil (100 microM), a putative Ca2+ transport antagonist, in contrast, did not prevent the monensin-induced acrosome reactions. Physiological concentrations of Na+ were needed for monensin to stimulate acrosome reactions, but high concentrations of Mg2+ prevented the monensin stimulation. The Ca2+ ionophore A23187 (75 nM) also required physiological concentrations of Na+ for the rapid induction of maximal acrosome reactions at an elevated pH (8.3) but did not require the presence of extracellular HCO3-. These studies suggest that a monovalent ionophore-induced rise in sperm intracellular Na+ concentrations is a pre-Ca2+ entry event, that stimulates an endogenous Ca2+/Na+ exchange that allows a Ca2+ influx which in turn induces the acrosome reaction. The possible regulatory role of the sperm intracellular pH and Na+, K+-ATPase during the capacitation process under physiological conditions is discussed.
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PMID:Bicarbonate- and calcium-dependent induction of rapid guinea pig sperm acrosome reactions by monovalent ionophores. 608 22


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