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)

Normal adults with normal protein intakes have a urinary NH4 excretion of 40 to 50 mmol/24 hours and a variable urinary pH. In cases of metabolic acidosis a urinary pH less than 5.5 suggests an extra-renal origin whilst a urinary pH greater than 5.5 is in favour of renal acidosis, but there are many exceptions to this rule. On the other hand, urinary NH4 excretion is always greater than 70 mmol/24 hours in the first case and less than 40-50 mmol/24 hours in the second; and the use of the urinary anionic gap (Na + K - Cl), negative in the first case and positive in the second, enables the two situations to be distinguished. The acidosis of nephron reduction is easily recognised in cases of severe renal failure with an increase in unmeasured plasma anions whilst tubular acidoses are accompanied by a hyperchloremia. Measurement of fractional HCO3 excretion after an oral loading dose of NaHCO3, preferably by TmCHO3 with respect to GFR, distinguishes proximal tubular acidosis (low TmHCO3) from distal tubular acidosis (normal or high TmHCO3). In the latter case, the presence of hypokalemia suggests a distal tubular acidosis either due to deficiency of the H(+)-ATPase pumps (absence of increased urinary pCO2 after oral loading dose of NaHCO3) or to the inability of the kidney to maintain a normal H+ gradient (normal increase of urinary pCO2. The presence of hyperkalemia suggests diseases associated with hypoaldosteronism (low or inappropriate serum aldosterone concentrations), abnormal transepithelial voltages or with a pseudo-hypoaldosteronism syndrome (high plasma aldosterone concentration). The prevalence of distal tubular acidosis with hyperkalemia is on the increase whilst tubular acidosis with hypokalemia remains rare.
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PMID:[Renal acidosis]. 223 3

The apical membrane of the rabbit corneal endothelium contains a potassium-selective ionic channel. In patch-clamp recordings, the probability of finding the channel in the open state (Po) depends on the presence of either HCO3- or Cl- in the bathing medium. In a methane sulfonate-containing bath, Po is less than 0.05 at all physiologically relevant transmembrane voltages. With 0 mM [HCO3-]o at +60 mV, Po was 0.085 and increased to 0.40 when [HCO3-]o was 15 mM. With 4 mM [Cl-]o at +60 mV, Po was 0.083 and with 150 mM Cl-, Po increased to 0.36. Low Po's are also found when propionate, sulphate, bromide, and nitrate are the primary bath anions. The mechanism of action of the anion-stimulated K+ channel gating is not yet known, but a direct action of pH seems unlikely. The alkalinization of cytoplasm associated with the addition of 10 mM (NH4)2SO4 to the bath and the acidification accompanying its removal do not result in channel activation nor does the use of Nigericin to equilibrate intracellular pH with that of the bath over the pH range of 6.8 to 7.8. Channel gating also is not affected by bathing the internal surface of the patch with cAMP, cGMP, GTP-gamma-s, Mg2+ or ATP. Blockers of Na/H+ exchange, Na(+)-HCO3- cotransport, Na(+)-K+ ATPase and carbonic anhydrase do not block the HCO3- stimulation of Po. Several of the properties of the channel could explain some of the previously reported voltage changes that occur in corneal endothelial cells stimulated by extracellular anions.
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PMID:Potassium channel in rabbit corneal endothelium activated by external anions. 231 91

Proton secretion in the renal medullary collecting duct is thought to occur via a luminal proton-ATPase. In order to determine what mechanism(s) participate in proton transport across medullary collecting duct (MCD) cells membranes, intracellular pH (pHi) regulation and proton extrusion rates were measured in freshly prepared suspensions of rabbit outer MCD cells. Cells were separated by protease digestion and purified by Ficoll gradient centrifugation. pHi was estimated fluorometrically using the entrapped intracytoplasmic pH indicator, 6-carboxyfluorescein. Proton extrusion rates were measured using a pH stat. The resting pHi of MCD cells was 7.19 +/- 0.05 (SE) in a nonbicarbonate medium of pH 7.30. When cells were acidified by exposure to acetate salts or by abrupt withdrawal of ammonium chloride, they exhibited pHi recovery to the resting pHi over a 5-min time-course. Depletion of greater than 95% of cellular ATP content by poisoning with KCN in the absence of glucose inhibited pHi recovery. ATP depletion inhibited proton extrusion from MCD cells. Treatment with N-ethylmaleimide also inhibited pHi recovery. In addition, cellular ATP content was dependent on transmembrane pH gradients, suggesting that proton extrusion stimulated ATP hydrolysis. Neither removal of extracellular sodium nor addition of amiloride inhibited pHi recovery. These results provide direct evidence that a plasma membrane proton-ATPase, but not a Na+/H+ exchanger, plays a role in proton transport and pHi regulation in rabbit MCD.
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PMID:Intracellular pH regulation and proton transport by rabbit renal medullary collecting duct cells. Role of plasma membrane proton adenosine triphosphatase. 241 58

Over a period of 2-3 wk after plating, cultured LLC-PK1 (pig kidney) cells develop a high capacity for Na+-dependent accumulation of alpha-methyl-D-glucoside. To further the analysis of this developmental process, we have developed a method for separating transporting from nontransporting cells on the basis of density changes accompanying hexose accumulation and the corresponding uptake of water. Volume regulation was prevented by suspending the cells in a K+-free, Cl(-)-free Na-gluconate medium. Na+-dependent transport was maintained at nearly control levels by addition of low concentrations of (NH4)2SO4, since NH+4 stimulates Na+-K+-ATPase at the K+ site and allows for the extrusion of accumulated Na+; NH+4-stimulated hexose uptake is ouabain sensitive. With volume regulation blocked but with transport near normal, transporting cells exhibited a phlorizin-sensitive density shift in methylglucoside-containing medium and could be separated from nontransporting cells on Percoll gradients.
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PMID:Separation of hexose-transporting from nontransporting LLC-PK1 cells on density gradients. 242 Jan 87

Fluorescein isothiocyanate-conjugated dextran (FITC-dextran) is internalized by endocytosis into the lysosome-like vacuoles of Saccharomyces cerevisiae (Makarow, M., 1985, EMBO (Eur. Mol. Biol. Organ.) J. 4:1861-1866). Here we show that under energy depletion conditions FITC-dextran accumulated in a cytoplasmic compartment, from which it could be chased to the vacuole when the energy block was removed. The internal pH of the intermediate compartment under energy depletion was determined by fluorometry to be 5.8. The pH could be raised by the lysosomotropic agent ammonium chloride, the protonophore carbonyl cyanide p-trifluoromethoxyphenyl-hydrazone (CCCP) and the ATPase inhibitors dicyclohexylcarbodiimide (DCCD) and sodium vanadate. The pH of the vacuole was found to be 6.5. It was raised by ammonium chloride, CCCP, and DCCD, but not with sodium vanadate. Efrapeptin had no effect on the internal pH of either compartment. By dissecting the endocytic pathway, two portions of the route leading to the vacuole could be studied separately. The internalization of FITC-dextran from the extracellular fluid to the intermediate compartment followed linear kinetics, was independent of energy, and occurred at temperatures of between 15 degrees and 37 degrees C. Transfer of the marker from the intermediate compartment to the vacuole required energy, took place at temperatures between 19 degrees and 37 degrees C, and had a half-time of 7 min at 37 degrees C. Transport of the marker from the exterior of the cell to the vacuole did not require acidic pH values in the intermediate compartment or the vacuole. We suggest that the cytoplasmic compartment revealed by FITC-dextran, under energy depletion, represents the equivalent of the endosomes of mammalian cells.
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PMID:Transport of a fluorescent macromolecule via endosomes to the vacuole in Saccharomyces cerevisiae. 243 74

Ca uptake by isolated SR membranes is inhibited by a cytosolic factor derived from heart cells. The inhibitory activity resides in the fraction of soluble proteins which precipitates in 30% saturated (NH4)2SO4 [Narayanan et al. (1982) Biochem. Biophys. Res. Commun. 108, 1158-1164]. In the present study, the mechanism of inhibition and the properties of the inhibitor have been analysed. The cytosolic inhibitor activates a Ca-release pathway, thereby uncoupling Ca loading and Ca-dependent ATPase activity of SR vesicles. Analysis of some general physiochemical characteristics of the endogenous inhibitor (e.g. thermolability, protein profile, solubility properties, interaction with ion-exchange resins) showed it to be distinct from free fatty acids which might contaminate the cytosolic fraction. Rather, it indicated that the inhibitor is related to myofibrillar or cytoskeletal structures. By means of an affinity-chromatography procedure using muscle albumin coupled to Sepharose 4B, a protein component was obtained from the inhibitor fraction. The characteristics of this protein closely resembled those of the endogenous inhibitor. A protein with similar characteristics was also obtained using a DNase-I-affinity chromatography column. The isolated protein was identified as actin. Inhibition of Ca uptake by the isolated inhibitor protein was reversed by muscle albumin and by stoichiometric amounts of DNase I. The potency of inhibition of various actin preparations was found to be highly variable and dependent on the tissue source. Our results indicate that particular minor actin isoforms present in heart cytosol display the greatest inhibitory activity (IC50 15-20 micrograms/ml).
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PMID:Characterization of heart cytosolic proteins capable of modulating calcium uptake by the sarcoplasmic reticulum. 2. Identification of actin isoforms with inhibitory activity. 243 34

A modified ATPase method for the simultaneous demonstration of capillaries and fiber types in skeletal muscle is presented. Muscle biopsies were obtained from mice, hamsters, rats, cats, and dogs, quick frozen, and sectioned at 8 microns in a cryostat. The frozen slides were fixed in a neutral formalin solution at 4 C for 5 min, and then incubated at 37 C for 1 hr in a medium containing ATP, Pb2+, and Ca2+ in a tris-maleate buffer (pH 7.2). Dilute (NH4)2S was used as a developer. To test the reliability of the proposed method, serial sections of each biopsy were stained separately for capillaries (amylase-PAS method) and for fiber types by a standard myosin ATPase (m-ATPase) method. Fiber type percent and capillary parameters were determined for each biopsy. No difference in results was observed for parameters determined using the modified ATPase method compared to the standard capillary and fiber type staining methods. This modified technique is therefore suitable for the simultaneous demonstration of capillaries and fiber types in skeletal muscle.
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PMID:A histochemical method for the simultaneous demonstration of capillaries and fiber type in skeletal muscle. 244 Jan 55

Microspectrofluorimetry of the pH-sensitive, fluorescent dye 2',7'-biscarboxyethyl-5 (6)-carboxyfluorescein (BCECF) was used to measure intracellular pH (pHi) in single parietal cells (PC) of intact rabbit gastric glands during resting and stimulated conditions. In 61% of PC, histamine plus isobutylmethylxanthine (IBMX) (both 100 microM) caused a small increase in pHi, ranging from 0.04 to 0.21 pH units (average delta pHi = 0.09 +/- 0.04 units over a 6-min period). In the other 39% of PC, pHi remained constant or decreased slightly (maximum decrease was 0.10 unit). The specific inhibitors omeprazole (50 microM, blocks H+- K+-ATPase), 4,4'-diisothiocyanodihydrostilbene-2,2'-disulfonic acid (H2DIDS; 100-200 microM, blocks Cl-HCO3 exchange) and amiloride (1 mM, blocks Na-H exchange) were added to both resting and stimulated PC. In stimulated PC, omeprazole caused pHi to decrease by 0.08 unit, but this inhibitor had no effect on pHi of resting PC. H2DIDS caused pHi to increase in stimulated PC five times faster compared with resting PC. Amiloride or Na-free solution (which should reverse the Na-H exchanger and cause cellular acidification) caused pHi to decrease 2.5 or 5 times, respectively, more slowly in stimulated PC compared with resting PC. Also, recovery from NH4-induced acidification (due primarily to Na-H exchange) was 1.8 times faster (measured at pHi 6.7) in resting vs. in stimulated PC. During histamine plus IBMX-induced stimulation, increased H secretion by the H+-K+-ATPase at the apical membrane is accompanied by an increase in activity of the Cl-HCO3 exchanger at the serosal membrane.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Regulation of intracellular pH in resting and in stimulated parietal cells. 247 37

Madin-Darby canine kidney (MDCK) cells plated at confluence and incubated for 20 h in low (5 microM) Ca2+ have no tight junctions (TJs), and their Na+-K+-ATPase is randomly distributed over the surface. On transfer to normal Ca2+ levels (1.8 mM) ("Ca2+ switch"), TJs and transepithelial resistance develop quickly, trapping a considerable fraction (35%) of the surface Na+-K+-ATPase on the apical (incorrect) side. This misplaced enzyme is subsequently removed from this region or inactivated, demonstrating that polarization proceeds despite TJs. Simultaneously, the amount of Na+-K+-ATPase on the basolateral side increases in a higher proportion (125%), than could be accounted for by relocation of the misplaced apical enzyme. This incorporation is prevented by cycloheximide, ammonium chloride, primaquine, or chloroquine, suggesting that Na+-K+-ATPase originates in an intracellular pool and that its surface insertion requires synthesis of new enzyme or of a protein factor, since it is carried to the surface membrane through a mechanism of exocytosis. In summary, asymmetric distribution of ion pumps depends 1) on polarized insertion of Na+-K+-ATPase as well as 2) on removal or inactivation of misplaced enzyme.
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PMID:Repolarization of Na+-K+ pumps during establishment of epithelial monolayers. 248 Jul 15

We have studied the properties of membrane-bound ATPase of a facultatively anaerobic alkalophile. The enzyme could not be solubilized without detergent, suggesting an integral membrane protein. The activity was accelerated by NH4+ and acetate anion, and inhibited by NH3-. The enzyme required Mg2+ or Mn2+ as a divalent cation for the maximal activity. In addition to ATP, the enzyme utilized other triphosphates of nucleosides as a substrate, but not di- nor monophosphates. The enzyme was suggested to crossreact with an antibody against the alpha-subunit of Na+/K+-ATPase from dog kidney.
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PMID:Characterization of the membrane-bound ATPase from a facultatively anaerobic alkalophile. 252 97


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