Characterization of ATP-dependent monoglucuronosyl bilirubin transport across rat canalicular membrane vesicles

Bilirubin conjugates are secreted from hepatocytes into bile. Monoglucurono syl bilirubin is an endogenous substrate for the multidrug resistance prote in ?, which is located in rat hepatocyte canalicular membrane. We have char acterized this ATP-dependent transport using rat canalicular membrane vesic les. Monoglucuronosyl bilirubin, H-3-labeled in the glucuronosyl moiety, wa s synthesized enzymatically using recombinant UDP-glycosyltransferase 1Al, and was stabilized with ascorbate. The rate for ATP-dependent transport of monoglucuronosyl bilirubin (at 0.5 muM) was 7.3 +/- 1.1 pmol mg protein(-1) min(-1) and the K-m value was 1.3 +/- 0.4 muM. This is the first time to d emonstrate this kinetic constant of monoglucuronosyl bilirubin for the rat hepatocyte canalicular membrane. The K-m value is similar to one for recomb inant rat multidrug resistance protein 2. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.