Fehrenbach Thomas, Cui Yunhai, Faulstich Heinz, Keppler Dietrich
Division of Tumor Biochemistry, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 280, D-69120, Heidelberg, Germany.
Naunyn Schmiedebergs Arch Pharmacol. 2003 Nov;368(5):415-20. doi: 10.1007/s00210-003-0814-4. Epub 2003 Oct 3.
Phalloidin, the major phallotoxin of the mushroom Amanita phalloides, enters hepatocytes by a carrier-mediated mechanism. The molecular identity of the transport proteins mediating phalloidin uptake was so far unknown. Earlier studies in rat liver indicated that phalloidin may share a common mechanism of uptake with organic anions like bile salts. In the current study on human transporters, we analyzed the uptake of phalloidin into transfected HEK293 cells stably expressing the recombinant hepatocyte-specific organic anion uptake transporters OATP2 (also termed OATP1B1, OATP-C, LST1, symbol SLC21A6) or OATP8 (OATP1B3 or SLC21A8). Time-dependent uptake of phalloidin was observed with SLC21A6-expressing cells and was inhibited by typical substrates of SLC21A6 such as bromosulfophthalein or cholyltaurine. A K(m) value of 39+/-11 micro M was determined for SLC21A6-mediated phalloidin uptake. Additional inhibitors of phalloidin uptake mediated by SLC21A6 included the immunosuppressive drugs cyclosporin A, FK506, and rapamycin, whereas alpha-amanitin was only a weak inhibitor. Cyclosporin A was a most potent competitive inhibitor for SLC21A6-mediated phalloidin transport with a K(i) value of 51 nM.
鬼笔环肽是毒鹅膏菌的主要鬼笔毒素，通过载体介导的机制进入肝细胞。迄今为止，介导鬼笔环肽摄取的转运蛋白的分子身份尚不清楚。早期对大鼠肝脏的研究表明，鬼笔环肽可能与胆盐等有机阴离子具有共同的摄取机制。在当前关于人类转运蛋白的研究中，我们分析了鬼笔环肽在稳定表达重组肝细胞特异性有机阴离子摄取转运蛋白OATP2（也称为OATP1B1、OATP-C、LST1，符号为SLC21A6）或OATP8（OATP1B3或SLC21A8）的转染HEK293细胞中的摄取情况。在表达SLC21A6的细胞中观察到鬼笔环肽的时间依赖性摄取，并受到SLC21A6的典型底物如溴磺酞或牛磺胆酸的抑制。测定SLC21A6介导的鬼笔环肽摄取的K(m)值为39±11微摩尔。SLC21A6介导的鬼笔环肽摄取的其他抑制剂包括免疫抑制药物环孢素A、FK506和雷帕霉素，而α-鹅膏菌素只是一种弱抑制剂。环孢素A是SLC21A6介导的鬼笔环肽转运的最有效竞争性抑制剂，K(i)值为51纳摩尔。
