title: Properties of (Na+ plus K+)-activated ATPase in rat liver plasma membranes enriched with bile canaliculi.
abstract: Liver plasma membranes enriched in bile canaliculi were isolated from rat liver by a modification of the technique of Song et al. (J. Cell Biol. (1969) 41, 124-132) in order to study the possible role of ATPase in bile secretion. Optimum conditions for assaying (Na+ plus K+)-activated ATPase in this membrane fraction were defined using male rats averaging 220 g in weight. (Na+ plus K+)-activated ATPase activity was documented by demonstrating specific cation requirements for Na+ and K+, while the divalent cation, Ca(2+), and the cardiac glycosides, ouabain and scillaren, were inhibitory. (Na+ plus K+)-activated ATPase activity averaged 10.07 plus or minus 2.80 mumol Pi/mg protein per h compared to 50.03 plus or minus 11.41 for Mg(2+)-activated ATPase and 58.66 plus or minus 10.07 for 5'-nucleotidase. Concentrations of ouabain and scillaren which previously inhibited canalicular bile secretion in the isolated perfused rat liver produced complete inhibition of (Na+ plus K+)-activated ATPase without any effect on Mg(2+)-activated ATPase. Both (Na+ plus K+)-activated ATPase and Mg(2+)-activated ATPase demonstrated temperature dependence but differed in temperature optima. Temperature induced changes in specific activity of (Na+ plus K+)-activated ATPase directly paralleled previously demonstrated temperature optima for bile secretion. These studies indicate that (Na+ plus K+)-activated ATPase is present in fractions of rat liver plasma membranes that are highly enriched in bile canaliculi and provide a model for further study of the effects of various physiological and chemical modifiers of bile secretion and cholestasis.
mesh_terms: D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D001646:Bile / Q000378:metabolism*; D001652:Bile Ducts / Q000201:enzymology* / Q000648:ultrastructure; D002018:Bufanolides / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology / Q000648:ultrastructure; D002712:Chlorides / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008099:Liver / Q000201:enzymology* / Q000648:ultrastructure; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D009708:Nucleotidases / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D013696:Temperature
chemical_list: D002018:Bufanolides; D002712:Chlorides; D010042:Ouabain; D012964:Sodium; D009708:Nucleotidases; D000251:Adenosine Triphosphatases; D008274:Magnesium; D011188:Potassium; D002118:Calcium