Analysis of multiplicity and polymorphism of drug transporters expressed in the liver.

肝脏和肾脏在外源物质的解毒中起着重要作用。众所周知，循环血液中的药物通过基底膜上的转运体进入肝脏，然后通过胆小管膜上的转运体排泄到胆汁中。对于负责摄取的转运体，钠离子依赖的胆汁酸转运体(Ntcp)和有机阴离子转运体1(Oatp1)已被鉴定。然而，还没有关于这些转运蛋白对肝脏药物摄取的贡献的定量研究。在本研究中，我们通过比较每种转运体对肝细胞和转基因哺乳动物细胞的药物摄取能力，确定了每种转运体在肝脏药物摄取中的作用。结果表明，钠离子依赖转运系统和独立转运系统都存在多重性。正在进行研究，以确定同源转运蛋白(如燕麦2和燕麦3)…的贡献更多。在胆小管跨膜转运方面，利用分离的大鼠和人胆小管膜泡，对有机阴离子的转运特性进行了研究。此外，我们还研究了小管多特异性有机阴离子转运体(CMOAT)的转运特性。此外，作为cMOAT的同源物，我们还克隆了大鼠和人多药耐药相关蛋白3(MRP3)。从哺乳动物细胞中分离的膜小泡的研究表明，MRP3可以接受葡萄糖醛酸苷而不是谷胱甘肽结合物作为良好的底物。因此，MRP1/2和MRP3的转运特性不同。在培养的大鼠和HepG2细胞中，MRP3是由苯巴比妥诱导的，提示MRP3表达水平的差异可能导致人类将异物和/或其结合物排泄到胆汁中的能力的个体间差异。较少

Liver, along with kidney, plays an important role in the detoxification of xenobiotics. It is well established that drugs in the circulating blood are taken up into the liver via transporters on the basal membrane, and then excreted into the bile via transporters on the bile canalicular membrane. Concerning the transporters responsible for the uptake, Na^+-dependent bile acid transporter (Ntcp) and organic anion transporter 1 (oatp1) have been identified. However, no quantitative studies have been performed on the contribution of these transporters to the hepatic uptake of drugs. In the present study, we determined the contribution of each transporter in hepatic drug uptake, by comparing the ability to take up drugs into hepatocytes and into cDNA-transfected mammalian cells. The results suggested the presence of multiplicity for both Na^+-dependent and independent transport systems. Studies are under way to determine the contribution of homologous transporters (such as oatp2 and oat 3) … More . Concerning the transport across the bile canalicular membrane, the transport properties of organic anions has been identified by using the isolated bile canalicular membrane vesicles isolated from rats and humans. In addition, we have characterized the transport properties of canalicular multispecific organic anion transporter (cMOAT) using the membrane vesicles isolated from cDNA-transfected cells. Moreover, as a homologue of cMOAT, we have cloned rat and human MRP3 (multidrug resistance associated protein 3). Studies with isolated membrane vesicles from mammalian cells transfected with MRP3 cDNA, it was demonstrated that MRP3 accepts glucuronides, but not glutathione-conjugates, as good substrates. Thus, the difference in the transport characteristics was demonstrated between MRP1/2 and 3. In rats and HepG2 cells in culture, MRP3 was induced by phenobarbital, suggesting that the difference in the expression level of MRP3 may result in the interindividual difference in the ability to excrete xenobiotics and/or their conjugates into the bile in humans. Less