Roles of Inner Blood-Retinal Barrier Organic Anion Transporter 3 in the Vitreous/Retina-to-Blood Efflux Transport of p-Aminohippuric Acid, Benzylpenicillin, and 6-Mercaptopurine

The purpose of the present study was to characterize rat or-ganic anion transporter (Oat) 3 (Oat3, Slc22a8) in the efflux transport at the inner blood-retinal barrier (BRB). Reverse tran-scription-polymerase chain reaction analysis showed that rat (r) Oat3 mRNA is expressed in retinal vascular endothelial cells (RVECs), but not rOat1 and rOat2 mRNA. The expression of Oat3 in the retina and human cultured retinal endothelial cells was further confirmed by Western blot analysis. Immunohisto-chemical staining in RVECs showed that rOat3 is colocalized with glucose transporter 1, but not P-glycoprotein, suggesting that rOat3 is possibly located at the abluminal membrane of the RVEC. The contribution of rOat3 to the efflux of [3H]p-amino-hippuric acid ([3H]PAH), [3H]benzylpenicillin ([3H]PCG), and [14C]6-mercaptopurine ([14C]6-MP), substrates of rOat3, fro