AJP - Gastrointestinal and Liver Physiology, Vol 244, Issue 2 116-G124, Copyright © 1983 by American Physiological Society
Role of inorganic electrolytes in bile acid-independent canalicular bile formation
M. S. Anwer and D. Hegner
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.
