Kusuhara Hiroyuki, He Zhonggui, Nagata Yoshinori, Nozaki Yoshitane, Ito Takashi, Masuda Hiroyuki, Meier Peter J, Abe Takaaki, Sugiyama Yuichi
Department of Biopharmaceutics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Pharm Res. 2003 May;20(5):720-7. doi: 10.1023/a:1023473216759.
It has been shown that transport(s) are involved in the uptake of estradiol 17beta glucuronide (E217betaG) by the choroid plexus (CP). The purpose of this study is to compare the substrate specificity of the transporter in the CP with those of rat organic anion transporting polypeptide 1 (rOatp1) and rOatp3.
The expression of rOatp1 and rOatp3 in rat CP was confirmed by RT-PCR and Western blot analyses. The substrate specificity of rOatp1 and rOatp3 was compared using cDNA-transfected LLC-PK1 cells. The uptake of E217betaG by rat isolated CP was determined by centrifugal filtration technique.
PCR analyses demonstrated that the mRNA expression of rOatp3 was abundant in the CP, whereas that of rOatp1 was low. Immunohistochemical staining revealed that rOatp3 is expressed on the apical membrane of the CP. Kinetic parameters (Km and Ki values) of rOatp3 were similar to those for rOatp1. The results of mutual inhibition study suggest that E217betaG and taurocholate share the same mechanism in the CP. Corticosterone, estrone-3-sulfate and indomethacin are moderate inhibitors, but no effects by digoxin, p-aminohippurate, benzylpenicillin and cimetidine were observed.
rOatp3 is most possible candidate transporter involved in the uptake of organic anions on the brush border membrane of the choroid epithelial cells.
已有研究表明，转运体参与了脉络丛（CP）对17β-葡萄糖醛酸雌二醇（E217βG）的摄取。本研究的目的是比较CP中转运体与大鼠有机阴离子转运多肽1（rOatp1）和rOatp3的底物特异性。
通过逆转录聚合酶链反应（RT-PCR）和蛋白质免疫印迹分析（Western blot）证实大鼠CP中rOatp1和rOatp3的表达。使用cDNA转染的LLC-PK1细胞比较rOatp1和rOatp3的底物特异性。采用离心过滤技术测定大鼠离体CP对E217βG的摄取。
PCR分析表明，rOatp3的mRNA在CP中表达丰富，而rOatp1的mRNA表达较低。免疫组织化学染色显示，rOatp3表达于CP的顶膜。rOatp3的动力学参数（Km和Ki值）与rOatp1相似。相互抑制研究结果表明，E217βG和牛磺胆酸盐在CP中具有相同的转运机制。皮质酮、硫酸雌酮和吲哚美辛是中度抑制剂，但未观察到地高辛、对氨基马尿酸、苄青霉素和西咪替丁有抑制作用。
rOatp3最有可能是参与脉络丛上皮细胞刷状缘膜上有机阴离子摄取的转运体。
