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 (0.02 seconds)

Ouabain exhibits a dose-dependent choleretic effect in the isolated perfused rat liver. Its uptake from the perfusate into the liver is maintained against a concentration gradient and becomes clearly saturated at higher perfusate concentrations. A low extracellular sodium concentration inhibits the rate of ouabain transfer into liver cells, resulting in a marked decrease of the maximal transport rate. Dibucaine completely abolishes the uptake of the glycoside by the isolated liver. Determination of Na-22 tracer fluxes suggests that ouabain uptake is accompanied by a net flux of sodium into the cell, which seems to be due to a cotransport of sodium with ouabain rather than to the inhibition of the sinusoidal Na+ -K+ -ATPase. Sodium introduced into the cell in this way apparently is extruded into the bile canaliculi. The increase of isotonic bile flow, which is simultaneously observed, points to a dilution of the canalicular sodium gradient by water and electrolytes through an intercellular pathway. Our results present further evidence that bile secretion is controlled by transcellular sodium movements.
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PMID:Ouabain-mediated sodium uptake and bile formation by isolated perfused rat liver. 126 18

Recently, a beta subunit for the rat gastric H+,K(+)-ATPase (HK beta), which is structurally similar to the beta subunit of Na+, K(+)-ATPase, has been cloned and characterized. Using heterologous expression in yeast, we have tested the specificity of beta subunit assembly with different isoforms of the alpha subunit of Na+, K(+)-ATPase. Coexpression in yeast cells of the HK beta with both the sheep alpha 1 subunit and the rat alpha 3 subunit isoforms of Na+, K(+)-ATPase (alpha 1 and alpha 3, respectively) leads to the appearance of high-affinity ouabain-binding sites in yeast membranes. These ouabain-binding sites (alpha 1 plus HK beta, alpha 3 plus HK beta) have a high affinity for ouabain (Kd, 5-10 nM) and are expressed at levels similar to those formed with the rat beta 1 subunit of Na+, K(+)-ATPase (beta 1) (alpha 1 plus beta 1 or alpha 3 plus beta 1). Potassium acts as a specific antagonist of ouabain binding by alpha 1 plus HK beta and alpha 3 plus HK beta just like sodium pumps formed with beta 1. Sodium pumps formed with the HK beta, however, show quantitative differences in their affinity for ouabain and in the antagonism of K+ for ouabain binding. These data suggest that the structure of the beta subunit may play a role in sodium pump function.
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PMID:High-affinity ouabain binding by yeast cells expressing Na+, K(+)-ATPase alpha subunits and the gastric H+, K(+)-ATPase beta subunit. 131 69

Erythrocytes from 15 patients with cystic fibrosis (CF) aged 8 mo to 22 y (mean age 12.8 y) were analyzed for Na+,K(+)-ATPase activity and sodium, potassium, and ATP concentrations. Sodium concentrations and Na(+)-K+ ratio of erythrocytes were statistically significantly lower in the CF patients [6.6 (SD 1.9) versus 9.2 (SD 1.1) mmol/L (p less than 0.01) and 0.070 (SD 0.023) versus 0.104 (SD 0.016) mmol/L (p less than 0.01), respectively]. The Na+,K(+)-ATPase activity was similar compared with that of reference individuals [536 (SD 100) versus 488 (SD 92) nmol inorganic phosphate/mg protein/h]. Intraerythrocyte sodium concentration and Na(+)-K+ ratio were thus lower in relation to the recorded Na+,K(+)-ATPase activities in controls, indicating a change of the passive transmembrane movements of sodium ions in CF. There was a rise of erythrocyte sodium and Na(+)-K+ ratio despite unchanged Na+,K(+)-ATPase activity after regular infusion of a fat emulsion rich in essential fatty acids, inferring that an altered membrane composition by essential fatty acid deficiency could explain the low intracellular sodium concentration in CF.
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PMID:Erythrocyte sodium-potassium transport in cystic fibrosis. 131 37

Gentamicin can cause proximal tubule necrosis. We have shown that inhibition of PT Na+,K(+)-ATPase activity is rapidly induced by gentamicin. We have now investigated whether manipulations known to attenuate the negative effects of gentamicin on renal excretory capacity, i.e. high calcium intake and L-thyroxine treatment, will also attenuate gentamicin-induced inhibition of Na+,K(+)-ATPase activity and ameliorated signs of proximal tubule damage. Rats were gentamicin- or vehicle-treated for 7 days. Sub-groups were given 4% calcium (Ca) supplements or L-thyroxine 20 micrograms 100 g-1 body weight daily. Gentamicin significantly reduced the glomerular filtration rate and increased the urinary excretion of the proximal tubule lysosomal enzyme, N-acetyl-beta-D-glucosaminidase. Gentamicin significantly reduced proximal tubule Na+,K(+)-ATPase activity, measured in single permeabilized proximal tubule segments. Sodium excretion was inversely correlated to proximal tubule Na+,K(+)-ATPase activity. Both calcium and L-thyroxine alleviated all gentamicin-induced side-effects on renal function as well as on proximal tubule Na+,K(+)-ATPase activity. Calcium and L-thyroxine had no significant effect on renal function. L-thyroxine, but not calcium, increased proximal tubule Na+,K(+)-ATPase activity in control rats. Renal cortical tissue gentamicin concentration was not influenced by calcium but was significantly lowered by L-thyroxine. Two procedures which, via different mechanisms, afford protection from gentamicin-induced changes in renal function also give protection from gentamicin-induced inhibition of Na+,K(+)-ATPase activity. This suggests that loss of integrity of the Na+,K(+)-ATPase enzyme contributes to gentamicin-induced nephrotoxicity.
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PMID:Calcium supplementation and thyroid hormone protect against gentamicin-induced inhibition of proximal tubular Na+,K(+)-ATPase activity and other renal functional changes. 132 21

Addition of lithium fluoride to a suspension of Na,K-ATPase undergoing turnover produced a slow (minutes) complete loss of ouabain-sensitive ATPase activity. Persistence of the effect in the presence of deferoxamine showed that fluoride inhibits independent of aluminum. The time course of onset of inhibition was adequately fit by a function corresponding to a monophasic transformation with a pseudo first-order rate constant (k(obs)). This constant varied hyperbolically with [Mg2+] (half-maximal effect at 9 mM Mg2+), whereas it increased with no sign of approaching saturation as the square of [F-], implying that inhibition requires binding of two fluorides/ATPase. The value of k(obs) was found to be increased by greater than 10-fold in the presence of potassium ([K+]1/2 = 0.6 mM) or ouabain. Sodium, ATP, and ADP, which favor the E1 form of the enzyme, had a protective effect. These results implicate the potassium-occluded MgE2(K2) complex as the main fluoride-susceptible form. Protection by Pi and orthovanadate suggests that fluoride exerts its effect at the phosphorylation site. Inhibition was reversible, although slowly, with t1/2 = 7 h at 37 degrees C. Sodium greatly accelerated reversal (t1/2 = 3 min with 150 mM Na+ present), and potassium antagonized this acceleration. The value of k(obs) for reactivation increased steeply with [Na+], with the sodium dependence being about the same at pH 8.0 as at pH 7.4. All of these effects have parallels to effects of fluoride on the sarcoplasmic reticulum CaATPase (Murphy, A. J., and Coll, R. J. (1992) J. Biol. Chem. 267, 5229-5235).
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PMID:Inhibition of the Na,K-ATPase by fluoride. Parallels with its inhibition of the sarcoplasmic reticulum CaATPase. 132 18

Sodium gradient-dependent 45Ca2+ transport occurred across the lens membrane both in the direction of Ca2+ uptake by inside-out vesicles and Ca2+ efflux after Ca2+ loading of right-side-out vesicles. Using the calcium ionophore, A23187, greater than 90% of the Na+ gradient-dependent Ca2+ uptake was estimated to be free Ca2+. A normal Na+ gradient was also required to maintain calcium homeostasis in the intact lens. The Na+ gradient contributed to Ca2+ efflux from lenses pre-loaded in medium containing 15 mM CaCl2. Therefore, a Na/Ca-exchange functions to control Ca efflux in rat lens, in addition to the Ca-ATPase. In the preweanling rat mature nuclear cataracts occurred by 96 h after subcutaneous injection of sodium selenite (30 nmol/g animal wt). A 3-5 fold increase of Ca2+ accompanied cataract formation. The loss of Ca2+ homeostasis can be detected by 48 h after treatment selenite treatment. At this time the initial rate of Na+ gradient-dependent Ca2+ uptake was 30% lower in lens vesicles from selenite-treated rats compared to controls. No significant reduction of Na+,K(+)-ATPase activity was detected. Altered Na/Ca-exchange may contribute directly to the loss of Ca2+ homeostasis that leads to nuclear cataract.
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PMID:Calcium efflux in rat lens: Na/Ca-exchange related to cataract induced by selenite. 132 93

Sphingomyelin liposomes and brain microsomes were oxidized by exposure to hydrogen peroxide and ferrous ion. Lipid peroxidation were measured by the formation of thiobarbituric acid- reactive substances (TBAR). Hydroxyl radical was detected using the spin- trapping technique. Incubation of sphingomyelin liposomes with H2O2-Fe2+ resulted in an increase in the formation of TBAR. Na(+)-K(+)-ATPase activity was markedly inhibited and the SH group content decreased during incubation of microsomes in the presence of H2O2-Fe2+. Sodium ferulate effectively inhibited TBAR formation, protected Na(+)-K(+)-ATPase activity and prevented the oxidative modification of SH groups. Spin-trapping experiments showed that sodium ferulate effectively scavenged the hydroxyl radicals.
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PMID:Effect of hydroxyl radical on Na(+)-K(+)-ATPase activity of the brain microsomal membranes. 133 Mar 32

The coprodaeum of the domestic hen maintained on a low-NaCl diet adapts by enhanced sodium transport. This study examines the adaptive response at the single cell and whole organ levels. Surface areas of apical (microvillous) and basolateral plasma membranes of columnar absorptive epithelial cells were estimated by use of ultrastructural stereology. The activities of succinic dehydrogenase (a mitochondrial enzyme) and ouabain-sensitive, potassium-dependent paranitrophenyl phosphatase (a sodium pump enzyme) were determined in tissue homogenates. Sodium, potassium-ATPase (pump enzyme) activity in cell membranes was localized by ultrastructural cytochemistry. Apical and basolateral membranes responded differently. In high-NaCl hens, the membrane signature of the average cell was 32 microns 2 (apical), 932 microns 2 (lateral) and 17 microns 2 (basal). Cells from low-NaCl hens had more apical membrane (49 microns 2 per cell) but essentially the same area of basolateral membrane. However, total surfaces per organ were greater for all membranes. Sodium pump enzymes were localized in basolateral membranes. Enzyme activities per unit mitochondrial volume and per unit basolateral membrane surface were higher in low-NaCl birds. These findings are discussed in the context of known mechanisms of transcellular sodium transport via apical ion channels and basolateral pumps.
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PMID:Structural and enzymatic studies on the plasma membrane domains and sodium pump enzymes of absorptive epithelial cells in the avian lower intestine. 133 14

The technique for X-ray microanalysis of frozen-hydrated bulk specimens was used to determine the intracellular and luminal fluid electrolyte concentrations in the proximal tubules of kidneys from chickens infected with infectious bronchitis virus. Eight days post-infection with this virus there were significant changes in the electrolyte composition when compared with values from normal control chickens. The intracellular sodium decreased from 43 to 36 mmol/l, the chloride fell from 41 to 31 mmol/l and the potassium went from 125 to 115 mmol/l. Sodium counts in the luminal fluid rose from .73 to 1.03 cps. These disturbances in electrolyte composition are consistent with alterations in sodium reabsorption in the proximal tubule due to decreased transport of sodium into the cells across the microvillus membrane. It appears that the Na-K-ATPase pump is unaffected. The results demonstrate the value of X-ray microanalysis methods for the study of electrolyte transport in pathologically affected cells and provide further information for the definition of viral-host cell interactions in the pathogenesis of viral disease. As a check on methodology two normal rat kidneys were analysed in the same way. Intracellular sodium and potassium concentrations were 22 and 138 mmol/l respectively.
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PMID:X-ray microanalytical investigation of the response of chicken proximal tubule cells to infection with avian infectious bronchitis virus. 164 25

The purpose of this study was to establish a method for preparing brush border membrane vesicles (BBMV) from bovine choroid plexus epithelium. Using the technique of divalent cation precipitation and differential centrifugation, we established and validated a procedure. The specific activity of Na+/K+ ATPase, a specific marker for choroid plexus brush border membranes, was enhanced greater than 14-fold in the final membrane preparation in comparison to its specific activity in the homogenate. The specific activities of marker enzymes for basolateral membranes, lysosomal membranes, and endoplasmic reticulum were enhanced less than fourfold in the final preparation. The presence of intact vesicles was ascertained by electron micrography and studies of osmotic sensitivity using isotopic uptake methods. Sodium-driven proline uptake was demonstrated confirming the presence of functional tightly sealed choroid plexus BBMV.
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PMID:Preparation of brush border membrane vesicles from bovine choroid plexus. 164 71


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