Functional reconstitution of the canalicular bile salt transport system of rat liver.
Recent studies have suggested that the canalicular bile salt transport system of rat liver corresponds to a 100-kDa membrane glycoprotein. In the present study we attempted to functionally reconstitute the 100-kDa protein into artificial proteoliposomes. Canalicular membrane proteins were solubilized with octyl glucoside in the presence of asolectin phospholipids. The extracts were treated with preimmune serum or the 100-kDa protein selectively immunoprecipitated with a polyclonal antiserum. Proteins remaining in the supernatant were then incorporated into proteoliposomes by gel-filtration chromatography. Canalicular proteoliposomes containing the 100-kDa protein exhibited transstimulatable taurocholate uptake that could be inhibited by 4,4'-diisothiocyanato-2,2'-stilbenedisulfonic acid (DIDS). In contrast, no DIDS-sensitive transstimulatable taurocholate uptake was found in 100-kDa protein-free canalicular proteoliposomes. However, when the immunoprecipitated 100-kDa protein was dissociated from the antibodies and exclusively incorporated into liposomes, reconstitution of DIDS-sensitive transstimulatable and electrogenic taurocholate anion transport was again positive. Although incorporation of solubilized basolateral membrane proteins into liposomes also resulted in a prompt reconstitution of Na+ gradient-driven taurocholate uptake, the anti-100-kDa antibodies had no effects on the reconstituted transport activity of basolateral proteins. Thus, the findings establish that the previously characterized canalicular-specific 100-kDa protein is directly involved in the transcanalicular secretion of bile salts.
Ruetz
S
S
Department of Medicine, University Hospital, Zurich, Switzerland.
Hugentobler
G
G
Meier
P J
PJ
D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism*; D001648:Bile Canaliculi / Q000378:metabolism*; D001653:Bile Ducts, Intrahepatic / Q000378:metabolism*; D001692:Biological Transport; D002352:Carrier Proteins / Q000032:analysis; D006023:Glycoproteins / Q000032:analysis; D008297:Male; D011510:Proteolipids / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
D001647:Bile Acids and Salts; D002352:Carrier Proteins; D006023:Glycoproteins; D011510:Proteolipids; C020485:proteoliposomes