Functional characterization of pH-sensitive organic anion transporting polypeptide OATP-B in human
Functional characterization of pH-sensitive organic anion transporting polypeptide OATP-B in human
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DOI：
10.1124/jpet.103.060194
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发表时间：
2004-02-01
影响因子：
3.5
通讯作者：
Tamai, I
中科院分区：
文献类型：
--
作者：
Nozawa, T;Imai, K;Tamai, I
在人小肠上皮细胞的顶膜上表达的人有机阴离子转运多肽OATP-B的pH敏感活性进行了功能表征。当OATP的典型底物雌酮-3-硫酸酯的初始摄取动力学研究时，我们观察到V-max随着pH从7.4降低到5.0而增加，而K-m的变化可以忽略不计。OATP-B介导的雌酮-3-硫酸盐摄取不依赖于钠、氯、碳酸氢盐或谷胱甘肽，而质子离子载体羰基氰化物对三氟甲氧基苯腙表现出pH依赖性抑制作用，表明质子梯度是OATP-B的驱动力。当OATP-B在人胚肾293细胞中表达时，对阴离子化合物的摄取活性表现出各种pH敏感性。在中性和酸性pH下，OATP-B均转运硫酸脱氢表雄酮、雌酮-3-硫酸酯和非索非那定，而雌二醇-17 β-葡糖苷酸、乙酸和乳酸则完全不转运。仅在酸性pH下观察到OATP-B对牛磺胆酸和普伐他汀的转运，证明了OATP-B的pH敏感性底物特异性。由于接近肠上皮细胞表面的生理pH为酸性，OATP-B在小肠中的作用可能与其他组织（如肝基底外侧膜）中的作用不同。尽管尚未完全确定OATP-B的驱动力，但澄清影响OATP-B活性的因素（如pH值）对于了解小肠中转运蛋白的生理学和药理学相关性至关重要。
The pH-sensitive activity of human organic anion transporting polypeptide OATP-B, which is expressed at the apical membrane of human small intestinal epithelial cells, was functionally characterized. When initial uptake of estrone-3-sulfate, a typical substrate of OATP, was studied kinetically, we observed an increase in V-max with decrease of pH from 7.4 to 5.0, whereas the change in K-m was negligible. OATP-B-mediated uptake of estrone-3-sulfate was independent of sodium, chloride, bicarbonate, or glutathione, whereas the proton ionophore carbonylcyanide p-trifluoromethoxyphenylhydrazone exhibited a pH-dependent inhibitory effect, suggesting that a proton gradient is a driving force for OATP-B. When OATP-B was expressed in human embryonic kidney 293 cells, uptake activities for anionic compounds showed various kinds of pH sensitivity. Dehydroepiandrosterone-sulfate, estrone-3-sulfate, and fexofenadine were transported by OATP-B at both neutral and acidic pH, whereas estradiol-17beta-glucuronide, acetic acid, and lactic acid were not transported at all. Transport of taurocholic acid and pravastatin by OATP-B was observed only at acidic pH, demonstrating a pH-sensitive substrate specificity of OATP-B. Because the physiological pH close to the surface of intestinal epithelial cells is acidic, the roles of OATP-B in the small intestine might be different from those in other tissues, such as liver basolateral membrane. Although the driving force for OATP-B has not been fully established, the clarification of factors, such as pH, that affect the OATP-B-activity is essential for an understanding of the physiological and pharmacological relevance of the transporter in the small intestine.