Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.3.5 (5'-nucleotidase)
 3,167 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of Triton WR-1339 and phenobarbital on ethinyl estradiol bile secretory failure were examined to determine the mechanism responsible for decreased bile salt excretion. When administered to ethinyl estradiol-treated rats, Triton WR-1339 restored bile salt independent bile flow and maximum taurocholate transport, whereas phenobarbital corrected bile flow only. Ethinyl estradiol decreased the activities of Na(+)-K(+)-ATPase, 5'-nucleotidase, while increasing the activities of Mg(++)-ATPase and alkaline phosphatase. In contrast to these heterogeneous changes in surface membrane enzyme activities, the number and affinity of [(14)C]cholic acid carriers were not altered. When administered in vivo or added directly to surface membrane fractions Triton WR-1339 restored the activities of Na(+)-K(+)-ATPase and Mg(++)-ATPase of rats treated with ethinyl estradiol through a process that did not require protein synthesis (unaffected by cycloheximide). Phenobarbital also restored the activity of Na(+)-K(+)-ATPase to control levels, but, unlike Triton WR-1339 it did not correct the defect responsible for reduced bile salt secretion. Ethinyl estradiol increased the concentration of cholesterol esters in surface membrane fractions. When administered to ethinyl estradiol-treated rats, Triton WR-1339 restored cholesterol ester concentrations to normal, whereas phenobarbital did not. These combined data suggest that decreased or altered bile salt carriers or reduced sodium driving forces resulting from impaired activity of Na(+)-K(+)-ATPase are not responsible for decreased bile salt excretion in ethinyl estradiol-treated rats. It is proposed that the diverse changes in surface membrane function, which are associated with ethinyl estradiol bile secretory failure, may be the result of a generalized alteration in membrane lipid structure.
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PMID:Reversal of ethinyl estradiol-induced bile secretory failure with Triton WR-1339. 624 35

Luminal extracellular ATP evoked a bumetanide-sensitive short-circuit current in cultured T84 cell epithelia (90.2 +/- 18.2 microA/cm2 at 100 microM ATP, apparent 50% effective concentration, 11.5 microM). ATP appeared to increase the Cl- conductance of the apical membrane but not the driving force for Cl- secretion determined by basolateral membrane K+ conductance. Specifically, the magnitude of Cl- secretion stimulated by ATP was independent of basal current, and forskolin pretreatment abolished subsequent stimulation of Cl- secretion by ATP. Whereas ATP stimulated modest production of adenosine 3',5'-cyclic monophosphate (cAMP) by T84 cells, ATP caused smaller increases in intracellular Ca2+ and inositol phosphate activities than the Ca(2+)-signaling Cl- secretagogue carbachol. An inhibitor of 5'-nucleotidase, alpha,beta-methyleneadenosine 5'-diphosphate, blocked most of the response to luminal ATP. The adenosine receptor antagonist 8-(p-sulfophenyl)theophylline blocked both the luminal ATP-dependent generation of cAMP and Cl- secretion when administered to the luminal but not submucosal bath. These results demonstrate that the Cl- secretion stimulated by luminal ATP is mediated by a A2-adenosine receptor located on the apical cell membrane. Thus metabolism of extracellular ATP to adenosine regulates the activity of cystic fibrosis transmembrane conductor regulator (CFTR) in the apical membrane of polarized T84 cells.
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PMID:Activation of CFTR Cl- conductance in polarized T84 cells by luminal extracellular ATP. 753 59

Luminal and abluminal membrane vesicles derived from bovine brain endothelial cells, the site of the blood-brain barrier, were fractionated in a discontinuous Ficoll gradient. A mathematical analysis was developed to determine the membrane distribution of membrane marker enzyme activities as well as the ratio of luminal to abluminal membrane in each fraction of the gradient. The results of this analysis indicate that gamma-glutamyl transpeptidase and amino acid transport system A are located on the luminal and abluminal membranes, respectively. Conversely, 5'-nucleotidase and alkaline phosphatase activities are evenly distributed between both membranes. Although Na+/K(+)-ATPase activity is primarily located on the abluminal membrane, approximately 25% of the activity is of luminal origin. Na+/K(+)-ATPase activities associated with each membrane showed different ouabain sensitivities, suggesting that different isoenzymes are located in luminal and abluminal membranes. The analytical procedure used in this study provides a quantitative means to determine the distribution of marker enzymes and transport proteins in partially purified membrane vesicle populations.
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PMID:Biochemical discrimination between luminal and abluminal enzyme and transport activities of the blood-brain barrier. 779 69