title: Blood-to-retina transport of creatine via creatine transporter (CRT) at the rat inner blood-retinal barrier.
abstract: The purpose of this study was to elucidate the mechanisms of blood-to-retina creatine transport across the blood-retinal barrier (BRB) in vivo and in vitro, and to identify the responsible transporter(s). The creatine transport across the BRB in vivo and creatine uptake in an in vitro model of the inner BRB (TR-iBRB2 cells) were examined using [(14)C]creatine. Identification and localization of the creatine transporter (CRT) were carried out by RT-PCR, western blot, and immunoperoxidase electron microscopic analyses. An in vivo intravenous administration study suggested that [(14)C]creatine is transported from the blood to the retina against the creatine concentration gradient that exists between the retina and blood. [(14)C]Creatine uptake by TR-iBRB2 cells was saturable, Na(+)- and Cl(-)-dependent and inhibited by CRT inhibitors, suggesting that CRT is involved in creatine transport at the inner BRB. RT-PCR and western blot analyses demonstrated that CRT is expressed in rat retina and TR-iBRB2 cells. Moreover, using an immunoperoxidase electron microscopic analysis, CRT immunoreactivity was found at both the luminal and abluminal membranes of the rat retinal capillary endothelial cells. In conclusion, CRT is expressed at the inner BRB and plays a role in blood-to-retina creatine transport across the inner BRB.
authors.affiliation: Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama 930-0194, Japan.
authors.forename: Toshihisa
authors.initials: T
authors.lastname: Nakashima
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Tomi
authors.forename: Kazunori
authors.initials: K
authors.lastname: Katayama
authors.forename: Masanori
authors.initials: M
authors.lastname: Tachikawa
authors.forename: Masahiko
authors.initials: M
authors.lastname: Watanabe
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Terasaki
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Hosoya
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D001813:Blood-Retinal Barrier / Q000502:physiology*; D015153:Blotting, Western; D002250:Carbon Radioisotopes; D002478:Cells, Cultured; D003401:Creatine / Q000378:metabolism* / Q000493:pharmacokinetics; D006801:Humans; D008297:Male; D026901:Membrane Transport Proteins / Q000378:metabolism*; D051379:Mice; D008815:Mice, Inbred Strains; D008954:Models, Biological; D010539:Permeability; D051381:Rats; D017208:Rats, Wistar; D012160:Retina / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D002250:Carbon Radioisotopes; D026901:Membrane Transport Proteins; C080679:creatine transporter; D003401:Creatine