Selective induction by phenobarbital of the electrogenic transport of glutathione and organic anions in rat liver canalicular membrane vesicles.

Glutathione is excreted into bile via a low affinity, electrogenic, ATP-independent transport system which is cis-inhibited and trans-stimulated by certain organic anions (Fernández-Checa, J. C., Takikawa, H., Horie, T., Ookhtens, M., and Kaplowitz N. (1992) J. Biol. Chem. 267, 1667-1673). This transport system differs from the sinusoidal carrier in several respects, such as affinity for transport and inhibitor specificity. Another differential aspect is the selective increase by phenobarbital pretreatment of GSH excretion into bile without changing the sinusoidal release into blood. To determine if phenobarbital induces the GSH transporter in the canalicular membrane and if this is reflected in the induction of organic anion transport, we have used rat liver canalicular (cLPM) and sinusoidal (bLPM) enriched membrane vesicles from liver of control (saline) and phenobarbital-treated rats. cLPM vesicles prepared from phenobarbital-pretreated rats exhibited a significant, 46% increase in Vmax for transport (9.02 +/- 0.3 versus 6.17 +/- 0.5 nmol/mg/15 s) without a change in the Km for GSH transport (14.0 +/- 1.1 versus 16.7 +/- 2.7 mM, respectively). Kinetic parameters for GSH transport in bLPM vesicles remained unchanged after phenobarbital treatment versus control (Vmax, 4.67 +/- 0.2 versus 4.77 +/- 0.2 nmol/mg/15 s; Km, 7.79 +/- 0.8 versus 6.95 +/- 0.8 mM, respectively). Phenobarbital treatment increased the electrogenic transport of [35S]sulfobromophthalein (BSP) (5 and 50 microM) but not the electrogenic uptake of [14C] glycocholic acid (10 and 200 microM). In addition, the ATP-dependent transport of [35S]BSP, [3H]leukotriene C4, and [14C]glycocholic acid into cLPM vesicles was not altered by phenobarbital treatment. The ATP-independent transport of [35S]BSP in cLPM was cis-inhibited and trans-stimulated by GSH, supporting the view that BSP and GSH share a common multispecific transporter. Thus, among the various canalicular transport systems, the multispecific electrogenic organic anion and GSH transport system is selectively induced by phenobarbital treatment.