Biliary transport of glutathione disulfide studied with isolated rat-liver canalicular-membrane vesicles

Abstract

Canalicular plasma membrane vesicles isolated from rat liver (right side out) were used to study glutathione disulfide (GSSG) transport. GSSG is transported into an osmotically sensitive compartment. Extrapolation to an external osmolarity of infinity indicates 35% binding after 10 min of incubation, e.g. as mixed disulfides between glutathione and SH-groups in membrane proteins. Glutathione disulfide uptake occurred with equal rates in the presence of KCl or NaCl. After equilibration, no significant GSSG concentration gradient across the canalicular membrane was found. The temperature dependence of uptake is consistent with a carrier-mediated transport for GSSG (Q10 X 1.6) and seems to exclude simple diffusion. Concentration dependence of GSSG uptake shows Michaelis-Menten kinetics at concentrations up to 1 mM; a Km of 0.4 mM and a V of 1.1 nmol X min-1 X mg protein-1 is calculated. At higher concentrations a linear dependence is observed without saturation kinetics. It is concluded that transport of glutathione disulfide is mediated by a carrier present in the canalicular membrane of the hepatocyte.