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FEBS Lett. 1999 Oct 1;459(1):128-32.

Functional analysis of rat renal organic anion transporter OAT-K1: bidirectional methotrexate transport in apical membrane.

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Department of Pharmacy, Kyoto University Hospital, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto, Japan.


Renal organic anion transporter OAT-K1 was stably transfected in MDCK cells and examined for its transport characteristics and membrane localization. OAT-K1 mediated both uptake and efflux of methotrexate in the apical membranes. Immunoblotting showed that the apparent molecular mass of the expressed OAT-K1 was 50 kDa, which was comparable to that found in the rat renal brush-border membranes. The OAT-K1-mediated methotrexate transport was significantly inhibited in the presence of several organic anions such as folate and sulfobromophthalein. These findings suggest that OAT-K1 mediates bidirectional methotrexate transport across the apical membranes, and may be involved in the renal handling of methotrexate.

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