Bumetanide is not transported by the Ntcp or by the oatp: evidence for a third organic anion transporter in rat liver cells

Abstract The loop diuretic bumetanide which inhibits hepatic bile acid uptake competitively according to its transport kinetics has been proposed to serve as a substrate of a multispecific bile acid transport system in liver parenchymal cells. However, when the in vitro transcripts of two cloned hepatic bile acid uptake carriers, the Ntcp (Na + /taurocholate cotransporting polypeptide) and the oatp (organic anion transporting polypeptide), was expressed for three days in Xenopus laevis oocytes [ 3 H]bumetanide uptake was not increased although bile acid uptake was stimulated. The data presented show that bumetanide is taken up by a third organic anion transport system which is different from the cloned bile acid transporters.