Structure-specific inhibition by bile acids of adenosine triphosphate—dependent taurocholate transport in rat canalicular membrane vesicles

Abstract

The adenosine triphosphate (ATP)-dependent transport system is a major determinant of canalicular bile acid secretion. The system transports bile acids and neither organic cations nor non—bile acid organic anions, such as glucuronides or glutathione adducts. To define the structural specificity of the ATP-dependent system, the authors examined the ability of various bile acids to inhibit ATP-dependent taurocholate transport by rat liver canalicular membrane vesicles. Only bile acids with a negative charge inhibited transport, which was unaffected by side chain length. Conjugated, but not unconjugated, mono- and di-hydroxy bile acids inhibited transport. The presence of 7α- and 12α-hydroxylation also influenced inhibition of ATP-dependent taurocholate transport. Inhibition of transport by bile acids was kinetically competitive. These results suggest that the canalicular ATP-dependent bile acid transport system depends on bile acid side chain charge, conjugation, and hydroxylation.