Cationic amino acid transporter 1-mediated L-arginine transport at the inner blood-retinal barrier.
The purpose of this study was to identify the transporter mediating l-arginine transport at the inner blood-retinal barrier (BRB). The apparent uptake clearance of [(3)H]L-arginine into the rat retina was found to be 118 microL/(min.g retina), supporting a carrier-mediated influx transport of L-arginine at the BRB. [(3)H]L-arginine uptake by a conditionally immortalized rat retinal capillary endothelial cell line (TR-iBRB2 cells), used as an in vitro model of the inner BRB, was primarily an Na(+)-independent and saturable process with Michaelis-Menten constants of 11.2 microM and 530 microM. This process was inhibited by rat cationic amino acid transporter (CAT) 1-specific small interfering RNA as well as substrates of CATs, L-arginine, L-lysine, and L-ornithine. The expression of cationic amino acid transporter (CAT) 1 mRNA was 25.9- and 796-fold greater than that of CAT3 in TR-iBRB2 and magnetically isolated rat retinal vascular endothelial cells, respectively. The expression of CAT1 protein was detected in TR-iBRB2 cells and immunostaining of CAT1 was observed along the rat retinal capillaries. In conclusion, CAT1 is localized in retinal capillary endothelial cells and at least in part mediates L-arginine transport at the inner BRB. This process seems to be closely involved in visual functions by supplying precursors of biologically important molecules like nitric oxide in the neural retina.
Tomi
Masatoshi
M
Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Sugitani, Toyama, Japan.
Kitade
Naohisa
N
Hirose
Shirou
S
Yokota
Noriko
N
Akanuma
Shin-Ichi
S
Tachikawa
Masanori
M
Hosoya
Ken-ichi
K
D000818:Animals; D001120:Arginine / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D001813:Blood-Retinal Barrier / Q000187:drug effects / Q000502:physiology*; D027201:Cationic Amino Acid Transporter 1 / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D008297:Male; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012160:Retina / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D012171:Retinal Vessels / Q000166:cytology; D013997:Time Factors; D014162:Transfection / Q000379:methods; D014316:Tritium / Q000378:metabolism
D027201:Cationic Amino Acid Transporter 1; D034741:RNA, Small Interfering; D014316:Tritium; D001120:Arginine