title: Mechanism of glutathione S-conjugate transport in canalicular and basolateral rat liver plasma membranes.
abstract: Transport of S-(2,4-dinitrophenyl)glutathione (DNP-SG), a model compound of glutathione S-conjugates, was studied in purified canalicular and basolateral (i.e. sinusoidal and lateral) rat liver plasma membrane (LPM) vesicles. Incubation of canalicular LPM vesicles with DNP-SG in the presence of ATP resulted in an uptake of DNP-SG into the vesicles. In contrast, in basolateral LPM vesicles the initial rate of ATP-dependent DNP-SG uptake was 3-4-fold lower than that of the canalicular LPM. This suggests that the ATP-dependent glutathione S-conjugates transport is localized in the canalicular membrane of the hepatocytes. The rate of DNP-SG uptake into canalicular LPM vesicles exhibited saturation kinetics with apparent Km values of 4 microM for DNP-SG and 260 microM for ATP. The DNP-SG uptake was inhibited by various glutathione S-conjugates and GSSG, not GSH. The bulkiness of S-substituent alkyl groups in the conjugates and cysteinylglycine of glutathione are essential for the inhibition. In contrast to the ATP-dependent process, the uptake of DNP-SG to basolateral LPM in the presence of KCl was 4-fold higher than that of canalicular LPM. The rate of DNP-SG uptake was enhanced by a valinomycin-induced K+ diffusion potential, and was inhibited by GSH. These results suggest that electrogenic transport of glutathione S-conjugates is localized in the basolateral membrane of the hepatocytes. These studies provide evidence that the ATP-dependent canalicular transport system functions in biliary secretion of glutathione S-conjugates.
authors.affiliation: Institute of Scientific and Industrial Research, Osaka University, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Y
authors.initials: Y
authors.lastname: Sogame
authors.forename: H
authors.initials: H
authors.lastname: Hara
authors.forename: K
authors.initials: K
authors.lastname: Hayashi
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001648:Bile Canaliculi / Q000378:metabolism*; D001653:Bile Ducts, Intrahepatic / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D005978:Glutathione / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008297:Male; D011189:Potassium Chloride; D051381:Rats; D011919:Rats, Inbred Strains; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D014634:Valinomycin; C030190:S-(2,4-dinitrophenyl)glutathione; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D005978:Glutathione