| Co-Investigator(Kenkyū-buntansha) |
ITO Kiyomi Faculty of Pharmaceutical Sciences, Kitasato University Assistant Professor, 薬学部, 講師 (60232435)
KATO Yukio Graduate School of Pharm.Sci., The Univ.of Tokyo Research Associate, 大学院・薬学系研究科, 助手 (30251440)
SUGIYAMA Yuichi Graduate School of Pharm.Sci., The Univ.of Tokyo Professor, 大学院・薬学系研究科, 教授 (80090471)
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| Research Abstract |
Liver, along with kidney, plays an important role in the detoxification of xenobiotics. In the present study, we have performed the cDNA cloning of canalicular multispecific organic anion transporter (cMOAT) and examined its function by using the membrane vesicles isolated from NIH3T3 cells transfected with this cDNA.By examining the transport properties of organic anions with isolated bile canalicular membrane vesicles (CMVs), we have also suggested the presence of multiplicity for the transporters located on the bile canalicular membrane. In addition, cDNA cloning of cMOAT family members was performed. With RT-PCR, we could amplify cDNA fragments of MRP3 and 6 from the liver of Eisai hyperbilirubinemic rats whose cMOAT function is hereditarily defective. We also succeeded in the cDNA cloning of full length rat and human MRP3 and rat MRP6. For MRP3, the cDNA-transfected cells were prepared to isolate the membrane vesicles. With thus prepared membrane vesicles, we could determine the s
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ubstrate specificity of MRP3. Although MRP3 accepts glucuronide conjugates as good substrates, glutathione conjugates were only poor substrates ; the transport properties of MRP3 were quite different from those of MRP1/2. Moreover, we have found that MRP3 is expressed in normal human liver and that its expression in HepG2 cells is induced by phenobarbital. We have also characterized the transport properties of organic anions using the isolated CMVs from rats and humans. Although comparable transport activity has been found among these two species, the transport activity of glutathione conjugates in humans was 1/5 of that in rats. If we consider the fact that MRP3 accepts glucuronide conjugates, but not glutathione conjugates, as good substrates and that MRP3 is expressed in normal human liver, but not in normal rat liver, it is suggested that the difference in the transport activity between rat and human CMVs can be accounted for by the difference in MRP3 expression levels. Since rat and human MRP3 are inducible, it is plausible that the difference in MRP3 expression level may result in the interindividual difference in the biliary excretion activity. Less
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