Vol. 63, Issue 3, 532-537, March 2003

In Vitro Study of the Functional Expression of Organic Anion Transporting Polypeptide 3 at Rat Choroid Plexus Epithelial Cells and Its Involvement in the Cerebrospinal Fluid-to-Blood Transport of Estrone-3-Sulfate

Sumio Ohtsuki, Takuya Takizawa, Hitomi Takanaga, Nobuyuki Terasaki, Takeo Kitazawa, Masako Sasaki, Takaaki Abe, Ken-ichi Hosoya, and Tetsuya Terasaki

Department of Molecular Biopharmacy and Genetics, Graduate School of Pharmaceutical Sciences (S.O., T.Ta., H.T., N.T., T.K., M.S., T.Te.), and New Industry Creation Hatchery Center (S.O., H.T., T.Te.), Tohoku University, Sendai, Japan; CREST (S.O., H.T., K.H., T.Ta.) and PREST (T.A.) of Japan Science and Technology Corporation, Japan (S.O., H.T., K.H., T.Ta.); Division of Nephrology, Endocrinology and Vascular Medicine, Department of Medicine, Tohoku University School of Medicine, Sendai, Japan (T.A.); and Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Toyama, Japan (K.H.)

The cerebrospinal fluid-to-blood efflux transport of estrone-3-sulfate (E₁S) via the blood-cerebrospinal fluid barrier (BCSFB) may play an important role in regulating E₁S levels in the brain. Here, we investigated the efflux transport of E₁S at the BCSFB using conditionally immortalized rat choroid plexus epithelial cells (TR-CSFB) and identified the responsible transporter. The [³H]E₁S uptake by TR-CSFB cells was composed of saturable and nonsaturable components, and the K_m and V_max values of the saturable component were determined to be 16.8 ± 5.1 µM and 12.3 ± 2.3 pmol/min/mg of protein, respectively. [³H]E₁S uptake was inhibited by probenecid, cholate, taurocholate, sulfobromophthalein, dehydroepiandrosterone sulfate, triiodothyronine, thyroxin, and digoxin but not by p-aminohippuric acid, -aminobutyric acid, or methotrexate, suggesting the involvement of organic anion transporting polypeptide (oatp) in the uptake. Reverse transcription-polymerase chain reaction analysis revealed that oatp3 was expressed in TR-CSFB cells and isolated rat choroid plexus, although oatp1 was not detected in either. Xenopus laevis oocytes expressing oatp3 exhibited [³H]E₁S uptake activity with a K_m of 8.09 ± 2.83 µM and V_max of 8.02 ± 0.87 pmol/h/oocyte. Moreover, oatp3 is localized at the brush-border membrane of choroid plexus epithelial cells. These results suggest that oatp3 is involved in the E₁S efflux transport at the BCSFB.