Fernández-Checa J C, Ookhtens M, Kaplowitz N
Department of Medicine, University of Southern California School of Medicine, Los Angeles 90033.
J Biol Chem. 1993 May 25;268(15):10836-41.
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.
谷胱甘肽通过一种低亲和力、电驱动、不依赖ATP的转运系统排泄到胆汁中，该系统受到某些有机阴离子的顺式抑制和反式刺激（费尔南德斯 - 切卡，J.C.，滝川，H.，堀江，T.，奥克滕斯，M.，和卡普洛维茨，N.（1992年）《生物化学杂志》267卷，1667 - 1673页）。这个转运系统在几个方面与窦状隙载体不同，比如对转运的亲和力和抑制剂特异性。另一个不同之处是苯巴比妥预处理可选择性增加谷胱甘肽向胆汁中的排泄，而不改变其向血液中的窦状隙释放。为了确定苯巴比妥是否诱导胆小管膜中的谷胱甘肽转运体，以及这是否反映在有机阴离子转运的诱导上，我们使用了来自对照（生理盐水）和苯巴比妥处理大鼠肝脏的富含胆小管（cLPM）和窦状隙（bLPM）的膜囊泡。从苯巴比妥预处理大鼠制备的cLPM囊泡的转运Vmax显著增加了46%（9.02±0.3对6.17±0.5 nmol/mg/15 s），而谷胱甘肽转运的Km没有变化（分别为14.±1.1对16.7±2.7 mM）。苯巴比妥处理后，bLPM囊泡中谷胱甘肽转运的动力学参数与对照相比保持不变（Vmax，4.67±0.2对4.77±0.2 nmol/mg/15 s；Km，7.79±0.8对6.95±0.8 mM）。苯巴比妥处理增加了[35S]磺溴酞钠（BSP）（5和50 microM）的电驱动转运，但没有增加[14C]甘氨胆酸（10和200 microM）的电驱动摄取。此外，苯巴比妥处理未改变[35S]BSP、[3H]白三烯C4和[14C]甘氨胆酸向cLPM囊泡的ATP依赖性转运。cLPM中[35S]BSP的ATP非依赖性转运受到谷胱甘肽的顺式抑制和反式刺激，支持了BSP和谷胱甘肽共享一个共同的多特异性转运体的观点。因此，在各种胆小管转运系统中，多特异性电驱动有机阴离子和谷胱甘肽转运系统受到苯巴比妥处理的选择性诱导。
