Influence of bile salts on hepatic mdr2 P-glycoprotein expression.

Mdr2 P-glycoprotein is expressed in the canalicular membrane of the mouse hepatocyte and is responsible for phospholipid secretion into bile. It is our hypothesis that it functions as a flippase in the translocation of phosphatidylcholine from the inner leaflet to the outer leaflet of the canalicular membrane. We have investigated the influence of different types of bile salts on the expression levels of mdr2 Pgp. Feeding mice a cholate-supplemented diet results in an increased mdr2 mRNA level, and this is accompanied by an increased biliary phospholipid secretion capacity. Cholate is a more hydrophobic bile salt than the main endogenous bile salt, muricholate. The induction of mdr2 gene expression and concomitant increase in phospholipid secretion are in line with the function of biliary phospholipids to inactivate the detergent action of hydrophobic bile salts.