Pharmaceutical Research

, Volume 18, Issue 9, pp 1262–1269 | Cite as

Functional Characterization of Human Organic Anion Transporting Polypeptide B (OATP-B) in Comparison with Liver-Specific OATP-C

  • Ikumi Tamai
  • Takashi Nozawa
  • Minako Koshida
  • Jun-ichi Nezu
  • Yoshimichi Sai
  • Akira Tsuji


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-17β-glucuronide and estrone-3-sulfate were measured using radiolabeled compounds.

Results. OATP-C transported both estrone-3-sulfate and estradiol-17β-glucuronide, whereas OATP-B transported only the former. OATP-C-mediated uptake of estrone-3-sulfate exhibited biphasic saturation kinetics, whereas transports of estradiol-17β-glucuronide by OATP-C and estrone-3-sulafte 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-17β-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.

organic anion transporter OATP estrogen conjugates liver 


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Copyright information

© Plenum Publishing Corporation 2001

Authors and Affiliations

  • Ikumi Tamai
    • 1
    • 2
  • Takashi Nozawa
    • 1
  • Minako Koshida
    • 1
  • Jun-ichi Nezu
    • 3
  • Yoshimichi Sai
    • 1
  • Akira Tsuji
    • 1
    • 2
  1. 1.Faculty of Pharmaceutical SciencesKanazawa UniversityKanazawaJapan
  2. 2.CREST, Japan Science and Technology CorporationKawaguchiJapan
  3. 3.Chugai Research Institute for Molecular Medicine Inc.IbarakiJapan

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