Eckhardt U, Schroeder A, Stieger B, Höchli M, Landmann L, Tynes R, Meier P J, Hagenbuch B
Division of Clinical Pharmacology and Toxicology, Department of Medicine, University Hospital, CH-8091 Zurich, Switzerland.
Am J Physiol. 1999 Apr;276(4):G1037-42. doi: 10.1152/ajpgi.1999.276.4.G1037.
The rat liver organic anion transporting polypeptide (Oatp1) has been extensively characterized mainly in the Xenopus laevis expression system as a polyspecific carrier transporting organic anions (bile salts), neutral compounds, and even organic cations. In this study, we extended this characterization using a mammalian expression system and confirm the basolateral hepatic expression of Oatp1 with a new antibody. Besides sulfobromophthalein [Michaelis-Menten constant (Km) of approximately 3 microM], taurocholate (Km of approximately 32 microM), and estradiol- 17beta-glucuronide (Km of approximately 4 microM), substrates previously shown to be transported by Oatp1 in transfected HeLa cells, we determined the kinetic parameters for cholate (Km of approximately 54 microM), glycocholate (Km of approximately 54 microM), estrone-3-sulfate (Km of approximately 11 microM), CRC-220 (Km of approximately 57 microM), ouabain (Km of approximately 3,000 microM), and ochratoxin A (Km of approximately 29 microM) in stably transfected Chinese hamster ovary (CHO) cells. In addition, three new substrates, taurochenodeoxycholate (Km of approximately 7 microM), tauroursodeoxycholate (Km of approximately 13 microM), and dehydroepiandrosterone sulfate (Km of approximately 5 microM), were also investigated. The results establish the polyspecific nature of Oatp1 in a mammalian expression system and definitely identify conjugated dihydroxy bile salts and steroid conjugates as high-affinity endogenous substrates of Oatp1.
大鼠肝脏有机阴离子转运多肽（Oatp1）主要在非洲爪蟾表达系统中被广泛表征为一种多特异性载体，可转运有机阴离子（胆盐）、中性化合物，甚至有机阳离子。在本研究中，我们使用哺乳动物表达系统扩展了这一表征，并使用一种新抗体证实了Oatp1在肝脏基底外侧的表达。除了磺溴酞钠[米氏常数（Km）约为3微摩尔]、牛磺胆酸盐（Km约为32微摩尔）和雌二醇-17β-葡萄糖醛酸苷（Km约为4微摩尔），这些底物先前已显示在转染的HeLa细胞中由Oatp1转运，我们还测定了在稳定转染的中国仓鼠卵巢（CHO）细胞中胆酸盐（Km约为54微摩尔）、甘氨胆酸盐（Km约为54微摩尔）、硫酸雌酮（Km约为11微摩尔）、CRC-220（Km约为57微摩尔）、哇巴因（Km约为3000微摩尔）和赭曲霉毒素A（Km约为29微摩尔）的动力学参数。此外，还研究了三种新底物，牛磺鹅去氧胆酸盐（Km约为7微摩尔）、牛磺熊去氧胆酸盐（Km约为13微摩尔）和硫酸脱氢表雄酮（Km约为5微摩尔）。结果证实了Oatp1在哺乳动物表达系统中的多特异性性质，并明确鉴定了共轭二羟基胆盐和类固醇共轭物为Oatp1的高亲和力内源性底物。
