title: 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.
abstract: The purpose of the present study was to characterize rat organic anion transporter (Oat) 3 (Oat3, Slc22a8) in the efflux transport at the inner blood-retinal barrier (BRB). Reverse transcription-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. Immunohistochemical 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 [(3)H]p-aminohippuric acid ([(3)H]PAH), [(3)H]benzylpenicillin ([(3)H]PCG), and [(14)C]6-mercaptopurine ([(14)C]6-MP), substrates of rOat3, from the vitreous humor/retina to the circulating blood across the inner BRB was evaluated using the microdialysis method. [(3)H]PAH, [(3)H]PCG, [(14)C]6-MP, and [(14)C] or [(3)H]d-mannitol, a bulk flow marker, were biexponentially eliminated from the vitreous humor after vitreous bolus injection. The elimination rate constant of [(3)H]PAH, [(3)H]PCG, and [(14)C]6-MP during the terminal phase was approximately 2-fold greater than that of d-mannitol. This efflux transport was reduced in the retinal presence of probenecid, PAH, and PCG, whereas it was not inhibited by digoxin. In conclusion, rOat3 is expressed at the inner BRB and involved in the vitreous humor/retina-to-blood transport of PAH, PCG, and 6-MP. This transport system is one mechanism to limit the retinal distribution of PAH, PCG, and 6-MP.
authors.affiliation: Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan. hosoyak@pha.u-toyama.ac.jp
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Hosoya
authors.forename: Akihide
authors.initials: A
authors.lastname: Makihara
authors.forename: Yuki
authors.initials: Y
authors.lastname: Tsujikawa
authors.forename: Daisuke
authors.initials: D
authors.lastname: Yoneyama
authors.forename: Shinobu
authors.initials: S
authors.lastname: Mori
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Terasaki
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Akanuma
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Tomi
authors.forename: Masanori
authors.initials: M
authors.lastname: Tachikawa
mesh_terms: D000818:Animals; D000838:Anions / Q000494:pharmacology; D000890:Anti-Infective Agents / Q000378:metabolism*; D000964:Antimetabolites, Antineoplastic / Q000378:metabolism*; D001693:Biological Transport, Active; D001813:Blood-Retinal Barrier / Q000502:physiology*; D015153:Blotting, Western; D002196:Capillaries / Q000378:metabolism; D003627:Data Interpretation, Statistical; D007150:Immunohistochemistry; D008297:Male; D015122:Mercaptopurine / Q000378:metabolism*; D017551:Microdialysis; D029362:Organic Anion Transporters, Sodium-Independent / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010400:Penicillin G / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012039:Regional Blood Flow; D012171:Retinal Vessels / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014822:Vitreous Body / Q000098:blood supply / Q000378:metabolism*; D010130:p-Aminohippuric Acid / Q000378:metabolism*
chemical_list: D000838:Anions; D000890:Anti-Infective Agents; D000964:Antimetabolites, Antineoplastic; D029362:Organic Anion Transporters, Sodium-Independent; C114338:organic anion transport protein 3; D015122:Mercaptopurine; D010400:Penicillin G; D010130:p-Aminohippuric Acid