THIOL-DISULFIDE EFFECTS ON HEPATIC GLUTATHIONE TRANSPORT - STUDIES INCULTURED RAT HEPATOCYTES AND PERFUSED LIVERS

In cultured rat hepatocytes, cystine led to an inhibition of GSH efflu x by lowering the V(max) by approximately 35% without affecting the K( m). The cystine-mediated inhibition of GSH efflux was rapid in onset ( < 1 h), with near maximum effect at 0.1 mM. Inhibition was still obser ved when cystine uptake was prevented. Cystine and sulfobromophthalein -GSH, a selective inhibitor of sinusoidal transport of GSH, did not ex hibit additive inhibitory effects on GSH efflux. Depletion of ATP or m embrane depolarization after cystine treatment were excluded as potent ial mechanisms. DTT not only reversed the cystine-mediated inhibition of GSH efflux, it stimulated GSH efflux up to 400-500%. The DTT effect was immediate in onset, reaching maximum after 30 min, and was partia lly reversed by cystine, suggesting that the two share a common site(s ) of action. DTT treatment did not alter cellular ATP levels or change the membrane potential. In cultured hepatocytes, DTT treatment increa sed the V(max) of GSH efflux by approximately 500% without affecting t he K(m). Inhibition of microtubular function and vesicular acidificati on did not affect basal or DTT stimulated efflux. Both cystine and DTT effects on sinusoidal GSH efflux were confirmed in perfused livers. I n summary, the capacity of the sinusoidal GSH transporter is markedly influenced by thiol-disulfide status.