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

肝脏，连同肾脏，在排毒中发挥重要作用的外源性药物。已经确定，循环血液中的药物通过基膜上的转运蛋白进入肝脏，然后通过胆小管膜上的转运蛋白排泄到胆汁中。关于摄取的转运体，Na^+依赖性胆汁酸转运体（Ntcp）和有机阴离子转运体1 （oatp1）已被确定。然而，还没有对这些转运蛋白对肝脏药物摄取的贡献进行定量研究。在本研究中，我们通过比较将药物带入肝细胞和进入转染dna的哺乳动物细胞的能力，确定了每种转运蛋白在肝脏药物摄取中的作用。结果表明，依赖Na^+的输运系统和独立输运系统都存在多重性。研究正在确定同源转运蛋白（如oatp2和oat3）的作用。关于胆小管膜的转运，利用大鼠和人分离的胆小管膜囊，鉴定了有机阴离子的转运特性。此外，我们还利用从转染dna的细胞中分离的膜泡表征了管状多特异性有机阴离子转运蛋白（cMOAT）的转运特性。此外，作为cMOAT的同源物，我们已经克隆了大鼠和人MRP3（多药耐药相关蛋白3）。对转染了MRP3 cDNA的哺乳动物细胞分离膜囊泡的研究表明，MRP3接受葡萄糖醛酸盐，而不是谷胱甘肽偶联物作为良好的底物。因此，MRP1/2和MRP1/2之间的输运特性存在差异。在培养的大鼠和HepG2细胞中，MRP3被苯巴比妥诱导，这表明MRP3表达水平的差异可能导致人类将外源性药物和/或其偶联物排泄到胆汁中的能力的个体间差异。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