Substrate specificity of the rat liver Na + -bile salt cotransporter in Xenopus laevis oocytes and in CHO cells

• Published in: American journal of physiology: Gastrointestinal and liver physiology 1998-02, Vol.274 (2), p.G370-G375
• Main Authors: Schroeder, Alice, Eckhardt, Uta, Stieger, Bruno, Tynes, Ronald, Schteingart, Claudio D, Hofmann, Alan F, Meier, Peter J, Hagenbuch, Bruno
• Format: Article
• Language: English
• ISSN: 0193-1857; 1522-1547
• DOI: 10.1152/ajpgi.1998.274.2.g370

It has been proposed that the hepatocellular Na -dependent bile salt uptake system exhibits a broad substrate specificity in intact hepatocytes. In contrast, recent expression studies in mammalian cell lines have suggested that the cloned rat liver Na -taurocholate cotransporting polypeptide (Ntcp) may transport only taurocholate. To characterize its substrate specificity Ntcp was stably transfected into Chinese hamster ovary (CHO) cells. These cells exhibited saturable Na -dependent uptake of [ H]taurocholate [Michaelis constant ( K ) of ∼34 μM] that was strongly inhibited by all major bile salts, estrone 3-sulfate, bumetanide, and cyclosporin A. Ntcp cRNA-injected Xenopus laevis oocytes and the transfected CHO cells exhibited saturable Na -dependent uptake of [ H]taurochenodeoxycholate ( K of ∼5 μM), [ H]tauroursodeoxycholate ( K of ∼14 μM), and [ C]glycocholate ( K of ∼27 μM). After induction of gene expression by sodium butyrate, Na -dependent transport of [ H]estrone 3-sulfate ( K of ∼27 μM) could also be detected in the transfected CHO cells. However, there was no detectable Na -dependent uptake of [ H]bumetanide or [ H]cyclosporin A. These results show that the cloned Ntcp can mediate Na -dependent uptake of all physiological bile salts as well as of the steroid conjugate estrone 3-sulfate. Hence, Ntcp is a multispecific transporter with preference for bile salts and other anionic steroidal compounds.