Brouwer K L, Durham S, Vore M
Department of Pharmacology, University of Kentucky College of Medicine, Lexington 40536.
Mol Pharmacol. 1987 Oct;32(4):519-23.
The transport of the cholestatic steroid glucuronide, 3H-estradiol-17 beta-(beta-D-glucuronide) (E2 17G), was examined in isolated female rat hepatocytes over a broad substrate concentration range (0.1-100 microM). Two different carrier systems were identified with the following kinetic parameters: Km1 = 4.54 microM; Vmax1 = 0.149 nmol/min/mg protein; Km2 = 149 microM; Vmax2 = 0.641 nmol/min/mg protein. Taurocholate and testosterone glucuronide selectively and competitively inhibited [3H]-E2 17G uptake at the high affinity site. Ki values calculated for taurocholate (43 microM) and testosterone glucuronide (28 microM) indicated that these two inhibitors were relatively weak competitors for this E2 17G transport site. Conversely, E2 17G inhibited [3H]taurocholate uptake into isolated hepatocytes (Ki = 43 microM). Bromosulfophthalein (10 microM) inhibited uptake of 0.5-50 microM [3H]-E2 17G by 55-85%, whereas morphine glucuronide (100 microM) had no significant effect on uptake of [3H]-E2 17G at these concentrations. The effects of taurocholate, testosterone glucuronide, bromosulfophthalein, and morphine glucuronide on [3H]-E2 17G uptake into isolated rat hepatocytes correlated with the ability of these agents to inhibit binding of [3H]-E2 17G to specific sites in rat liver plasma membranes. These data support the postulate that the two [3H]-E2 17G binding sites identified in female rat liver plasma membranes represent two distinct organic anion carriers and indicate that the high affinity site for [3H]-E2 17G represents a carrier that is shared by organic anions and bile acids.
在广泛的底物浓度范围（0.1 - 100微摩尔）内，对分离出的雌性大鼠肝细胞中胆汁淤积性类固醇葡萄糖醛酸苷——3H - 雌二醇 - 17β - （β - D - 葡萄糖醛酸苷）（E2 17G）的转运进行了研究。确定了两种不同的载体系统，其动力学参数如下：Km1 = 4.54微摩尔；Vmax1 = 0.149纳摩尔/分钟/毫克蛋白质；Km2 = 149微摩尔；Vmax2 = 0.641纳摩尔/分钟/毫克蛋白质。牛磺胆酸盐和睾酮葡萄糖醛酸苷在高亲和力位点选择性且竞争性地抑制[3H] - E2 17G的摄取。计算得出的牛磺胆酸盐（43微摩尔）和睾酮葡萄糖醛酸苷（28微摩尔）的Ki值表明，这两种抑制剂对于该E2 17G转运位点而言是相对较弱的竞争者。相反，E2 17G抑制[3H]牛磺胆酸盐摄取到分离的肝细胞中（Ki = 43微摩尔）。溴磺酚酞（10微摩尔）使0.5 - 50微摩尔[3H] - E2 17G的摄取减少55 - 85%，而吗啡葡萄糖醛酸苷（100微摩尔）在这些浓度下对[3H] - E2 17G的摄取没有显著影响。牛磺胆酸盐、睾酮葡萄糖醛酸苷、溴磺酚酞和吗啡葡萄糖醛酸苷对[3H] - E2 17G摄取到分离的大鼠肝细胞中的影响，与这些试剂抑制[3H] - E2 17G与大鼠肝细胞膜上特异性位点结合的能力相关。这些数据支持这样一种假设，即在雌性大鼠肝细胞膜中鉴定出的两个[3H] - E2 17G结合位点代表两种不同的有机阴离子载体，并表明[3H] - E2 17G的高亲和力位点代表一种有机阴离子和胆汁酸共用的载体。
