Characteristics of glycine transport across the inner blood-retinal barrier.
Although glycine plays a pivotal role in neurotransmission and neuromodulation in the retina and is present in high concentration in the retina, the source of retinal glycine is still unclear. The purpose of the present study was to investigate glycine transport across the inner blood-retinal barrier (inner BRB). [(14)C]Glycine transport at the inner BRB was characterized using a conditionally immortalized rat retinal capillary endothelial cell line (TR-iBRB2 cells) as an in vitro model of the inner BRB and in vivo vascular injection techniques. [(14)C]Glycine uptake by TR-iBRB2 cells was Na(+)- and Cl(-)-dependent, and concentration-dependent with Michaelis-Menten constants of 55.4 microM and 8.02 mM, and inhibited by glycine transporter 1 (GlyT1) and system A inhibitors. These uptake studies suggest that GlyT1 and system A are involved in [(14)C]glycine uptake by TR-iBRB2 cells. RT-PCR analysis demonstrated that GlyT1 and system A (encoding ATA 1 and ATA2) mRNA are expressed in TR-iBRB2 cells. An in vivo study suggested that [(14)C]glycine is transported from blood to the retina whereas [(14)C]alpha-methylaminoisobutyric acid, a selective substrate for system A, is not. In conclusion, GlyT1 most likely mediates glycine transport at the inner BRB and is expected to play an important role in regulating the glycine concentration in the neural retina.
Okamoto
Masashi
M
Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan.
Akanuma
Shin-ichi
S
Tachikawa
Masanori
M
Hosoya
Ken-ichi
K
D026924:Amino Acid Transport System A / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology; D001812:Blood-Brain Barrier / Q000378:metabolism*; D002461:Cell Line, Transformed; D002713:Chlorine / Q000378:metabolism; D005998:Glycine / Q000378:metabolism*; D050487:Glycine Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D012161:Retinal Artery / Q000166:cytology / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D026924:Amino Acid Transport System A; D050487:Glycine Plasma Membrane Transport Proteins; D012333:RNA, Messenger; C493266:Slc6a9 protein, rat; D002713:Chlorine; D012964:Sodium; D005998:Glycine