Role of inorganic electrolytes in bile acid-independent canalicular bile formation.
Ion-replacement studies were carried out in the isolated perfused rat liver to obtain insight into the role played by inorganic electrolytes in bile acid-independent canalicular bile flow (BAICF). The BAICF decreased significantly when Na+ (146 mM) was replaced by 120 mM K+, Rb+, Cs+, or choline and when Cl- (127 mM) was replaced by 120 mM acetate or isethionate; there was no reduction in BAICF when Na+ was replaced by Li+ (146 mM) and Cl- by NO-3. K+, Rb+, and Cs+, however, also caused a simultaneous decline in the perfusion rate. The BAICF decreased by 50% when HCO-3 was replaced by equimolar tricine; under this condition replacement of Cl- by NO-3, but not Na+ by Li+, decreased BAICF by 45%. Thus the hepatic transport of Cl- cannot be explained by simple diffusion only, and a special mechanism, probably Na+-coupled Cl- transport, may contribute about 30% of the BAICF. With Li+ replacing Na+ in the medium, the intracellular concentration of Li+ in isolated rat hepatocytes was less than that calculated for electrochemical equilibrium and was increased by 2 mM KCN, indicating active extrusion of this ion. Li+ was unable to activate Mg2+-ATPase of isolated rat liver plasma membranes, and 1 mM ouabain did not affect the Li+ distribution. These results suggest the potential importance of ion pumps other than Na+-K+-ATPase in BAICF.
D000818:Animals; D001646:Bile / Q000187:drug effects / Q000502:physiology*; D001647:Bile Acids and Salts / Q000494:pharmacology*; D002414:Cations, Monovalent; D002462:Cell Membrane / Q000201:enzymology; D004573:Electrolytes / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D001647:Bile Acids and Salts; D002414:Cations, Monovalent; D004573:Electrolytes; C030704:magnesium sodium potassium ATPase; D000254:Sodium-Potassium-Exchanging ATPase