Substrate specificity of the rat liver Na(+)-bile salt cotransporter in Xenopus laevis oocytes and in CHO cells.
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 [3H]taurocholate [Michaelis constant (K(m)) of approximately 34 microM] 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 [3H]taurochenodeoxycholate (Km of approximately 5 microM), [3H]tauroursodeoxycholate (Km of approximately 14 microM), and [14C]glycocholate (Km of approximately 27 microM). After induction of gene expression by sodium butyrate, Na(+)-dependent transport of [3H]estrone 3-sulfate (Km of approximately 27 microM) could also be detected in the transfected CHO cells. However, there was no detectable Na(+)-dependent uptake of [3H]bumetanide or [3H]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.
Schroeder
A
A
Department of Medicine, University Hospital, Zurich, Switzerland.
Eckhardt
U
U
Stieger
B
B
Tynes
R
R
Schteingart
C D
CD
Hofmann
A F
AF
Meier
P J
PJ
Hagenbuch
B
B
D000818:Animals; D016466:CHO Cells; D002352:Carrier Proteins / Q000378:metabolism*; D006224:Cricetinae; D004970:Estrone / Q000031:analogs & derivatives / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism*; D029363:Organic Anion Transporters, Sodium-Dependent; D051381:Rats; D013379:Substrate Specificity; D027981:Symporters; D013656:Taurocholic Acid / Q000493:pharmacokinetics; D014982:Xenopus laevis
D002352:Carrier Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D027981:Symporters; C071908:sodium-bile acid cotransporter; D004970:Estrone; D013656:Taurocholic Acid; C017296:estrone sulfate