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XB-ART-8183
Pharm Res 2001 Sep 01;189:1262-9. doi: 10.1023/a:1013077609227.
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Functional characterization of human organic anion transporting polypeptide B (OATP-B) in comparison with liver-specific OATP-C.

Tamai I , Nozawa T , Koshida M , Nezu J , Sai Y , Tsuji A .


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PURPOSE: To assess the functional characteristics of human organic anion transporter B (OATP-B) in comparison with those of the known, liver-specific OATP-C. METHODS: OATP-B or -C was expressed in HEK293 cells or Xenopus oocytes, and uptakes of estradiol-17beta-glucuronide and estrone-3-sulfate were measured using radiolabeled compounds. RESULTS: OATP-C transported both estrone-3-sulfate and estradiol-17beta-glucuronide, whereas OATP-B transported only the former. OATP-C-mediated uptake of estrone-3-sulfate exhibited biphasic saturation kinetics, whereas transports of estradiol-17beta-glucuronide by OATP-C and estrone-3-sulfate by OATP-B followed single-saturation kinetics. Inhibition kinetics showed that only the high-affinity site for estrone-3-sulfate on OATP-C was shared with glucuronide conjugates. Uptake of [3H]estrone-3-sulfate by OATP-B was inhibited by sulfate conjugates but not by glucuronide conjugates, whereas its uptake by OATP-C was inhibited by both types of conjugates. CONCLUSIONS: OATP-B accepted sulfate conjugates of steroids but not glucuronide conjugates, whereas OATP-C transported both types of steroid conjugates. Transport of estrone-3-sulfate by OATP-B and -C followed single- and biphasic-saturation kinetics, respectively, and the high-affinity site on OATP-C was the same as that for estradiol-17beta-glucuronide. Other OATPs, OATP-A and OATP-8, reportedly exhibit different preferences for steroid conjugates, and the specific recognition of sulfate conjugates seems to be unique to OATP-B.

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Species referenced: Xenopus
Genes referenced: slco1a2

References [+] :
Abe, Identification of a novel gene family encoding human liver-specific organic anion transporter LST-1. 1999, Pubmed