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)

At [Na+]o = 118 mM the concentrative transfer of cholic and taurocholic acid from the perfusate into the isolated rat liver displays saturation kinetics (taurocholate: V = 299 nmol-min-1-g-1, Km = 61 muM; Cholate: V=327 nmol-min-1-g-1, Km = 436 muM). Perfusion with an isotonic sodium-free medium did not change the feature of a carrier-mediated transport but did markedly reduce V without affecting Km (taurocholate: V = 65 nmol-min-1-g-1, Km = 78 muM; cholate: V = 104 nmol-min-1-g-1, Km = 354 muM). It was experimentally assured that the observed reduction of bile salt uptake was not a consequence of regurgitation of bile salts or due to an excessive intracellular accumulation during cholestasis in the sodium-free state. The rate of taurocholate efflux is very low when compared with the rapid rate of the uptake. A stimulatory action of extracellular sodium on this pathway was also observed. Inhibition of the (Na+ + K+)-ATPase by 1 mM ouabain resulted in a decrease of bile salt uptake. Activation of the enzyme by potassium readmission to a K+-deprived liver enhanced bile salt uptake. The immediate response to alteration of the enzyme activity suggests a close association of a fraction of bile acid active transport with the sodium pump.
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PMID:Investigations on the sodium dependence of bile acid fluxes in the isolated perfused rat liver. 13 26

We and others have published data that indicate that the role played by microtubules and microfilaments in biliary secretion is as follows: microtubules play a part in secretion and microfilaments play a part in the canalicular contraction. To further study the role of the cytoskeleton in canalicular contraction, we observed the contraction of bile canaliculi (BC) induced by vasopressin (VP) in cultured differentiated hepatocytes treated with several agents that selectively rearrange the cytoskeleton. The hepatocytes obtained from 14-day-old rats were cultured for 48 hours. The BC formed between the cells were dilated and closely sealed by junctional complexes. Ruthenium red stain showed that the junctional complexes of the BC were tightly sealed. Cytoskeletal changes were observed by double-labeled fluorescence microscopy. A spontaneous contraction of the BC was rarely seen during a 60-minute observation period in controls. When the hepatocytes were incubated with VP (10(-8) M), the canalicular contraction began at 30 minutes, gradually progressed, and was complete by 60 minutes. The contraction was reversed after 60 minutes of incubation in VP-free medium. In cytochalasin B-treated hepatocytes, actin appeared to form pools around the dilated BC, and the canalicular contraction after VP was rarely observed. In colchicine-treated hepatocytes, the microtubules were depolymerized. Although the BC appeared unaffected by colchicine alone, the canalicular contraction induced by VP was markedly decreased. beta-lumicolchicine had no effect on the cytoskeleton or on the canalicular contraction. Mg2(+)-ATPase histochemistry revealed that the BC that did not contract after VP contained little Mg2(+)-ATPase reaction product. When the BC contracted, diverticula came off to form diacytotic vesicles, as indicated by the presence of the BC marker enzyme reaction product within the vesicles. Colchicine treatment blocked the diacytotic process. This prevented the contraction stimulated by VP, because all of the routes of escape of the canalicular contents were blocked off, including diacytosis. In conclusion, the integrity of actin filaments and Mg2(+)-ATPase is necessary for VP-induced contraction, and the integrity of microtubules is essential for regurgitation of BC content (diacytosis).
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PMID:Role of cytoskeleton in canalicular contraction in cultured differentiated hepatocytes. 169 May 9

Myocardial Na+,K(+)-ATPase was studied in patients with aortic valve disease, and myocardial Na+,K(+)- and Ca(2+)-ATPase were assessed in spontaneously hypertensive rats (SHR) and hereditary cardiomyopathic hamsters using methods ensuring high enzyme recovery. Na+,K(+)-ATPase was quantified by [3H]ouabain binding to intact myocardial biopsies from patients with aortic valve disease. Aortic stenosis, regurgitation and a combination hereof were compared with normal human heart and were associated with reductions of left ventricular [3H]ouabain binding site concentration (pmol/g wet weight) of 56, 46 and 60%, respectively (p < 0.01). Na+,K(+)- and Ca(2+)-ATPases were quantified by K(+)- and Ca(2+)-dependent p-nitrophenyl phosphatase (pNPPase) activity determinations in crude myocardial homogenates from SHR and hereditary cardiomyopathic hamsters. When SHR were compared to age-matched Wistar Kyoto (WKY) rats an increase in heart-body weight ratio of 75% (p < 0.001) was associated with reductions of K(+)- and Ca(2+)-dependent pNPPase activities (mumol/min/g wet weight) of 42 (p < 0.01) and 27% (p < 0.05), respectively. When hereditary cardiomyopathic hamsters were compared to age-matched Syrian hamsters an increase in heart-body weight ratio of 69% (p < 0.001) was found to be associated with reductions in K(+)- and Ca(2+)-dependent pNPPase activities of 50 (p < 0.001) and 26% (p = 0.05), respectively. The reductions in Na+,K(+)- and Ca(2+)-ATPases were selective in relation to overall protein content and were not merely the outcome of increased myocardial mass relative to Na+,K(+)- and Ca(2+)-pumps. In conclusion, myocardial hypertrophy is in patients associated with reduced Na+,K(+)-ATPase concentration and in rodents with reduced Na+,K(+)- and Ca(2+)-ATPase concentrations. This may be of importance for development of heart failure and arrhythmia in hypertrophic heart disease.
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PMID:Reduced concentration of myocardial Na+,K(+)-ATPase in human aortic valve disease as well as of Na+,K(+)- and Ca(2+)-ATPase in rodents with hypertrophy. 908 35