Multispecific amphipathic substrate transport by an organic anion transporter of human liver.
BACKGROUND: Hepatic uptake of differently charged amphipathic endo- and xenobiotics is thought to occur via distinct carrier-mediated transport systems. Alternatively, a single rat organic anion transporting polypeptide ( oatp) has recently been demonstrated to mediate hepatocellular uptake of differently charged amphipathic substrates. AIM: To investigate whether a cloned human liver organic anion transporting polypeptide ( OATP) also can mediate charge- and class-independent hepatocellular uptake of amphipathic substrates. METHODS: Xenopus laevis oocytes were injected with OATP-cRNA. Sodium-independent uptake of estrone-3-sulfate, ouabain and the organic cation N-(4,4-azo-n-pentyl)-21-ajmalinium was compared in OATP-expressing and uninjected (or water injected) control oocytes. RESULTS: Our results indicate that OATP, in addition to bromosulfophthalein and bile salts, can also transport anionic estrone-3-sulfate (Km approximately 59 microM), neutral ouabain (K(m) approximately 5.5 mM) and cationic N-(4,4-azo-n-pentyl)-21-ajmalinium. For each of these compounds, OATP- mediated uptake was cis- inhibited by the OATP substrate taurochenodeoxycholate and the transport activities correlated well with the amounts of cRNA injected. CONCLUSION: Similar to the rat liver oatp, the human liver OATP can also mediate multispecific and charge-independent uptake of lipophilic amphipathic organic compounds. Thus, OATP may play an important role in the first pass clearance of drugs and other xenobiotics by the human liver.[1]References
- Multispecific amphipathic substrate transport by an organic anion transporter of human liver. Bossuyt, X., Müller, M., Meier, P.J. J. Hepatol. (1996) [Pubmed]
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