Glycine and L-arginine transport in cultured Müller glial cells (TR-MUL).
We have reported previously that creatine is biosynthesized from glycine and L-arginine in Müller cells, but the mechanism responsible for glycine and L-arginine uptake by Müller cells remains elusive. To explore this issue, [(14)C]glycine and [(3)H]L-arginine uptake by Müller cells was characterized using a conditionally immortalized rat Müller cell line (TR-MUL5 cells). [(14)C]Glycine uptake by TR-MUL5 cells was Na(+)- and Cl(-)-dependent, and a saturable process with Michaelis-Menten constants of 48.6 microM and 4.53 mM, and inhibited by glycine transporter 1 (GlyT1) and system A substrates. Under Cl(-)-free conditions, the high-affinity process was abolished. RT-PCR analysis demonstrated that GlyT1 and system A (encoding ATA1 and ATA2) mRNA are expressed in TR-MUL5 cells. These uptake studies suggest that GlyT1 and system A are involved in [(14)C]glycine uptake for the high- and low-affinity processes, respectively, in TR-MUL5 cells. [(3)H]l-Arginine uptake by TR-MUL5 cells was primarily an Na(+)-independent and saturable process with Michaelis-Menten constants of 15.0 and 403 microM. This process was inhibited by substrates of cationic amino acid transporter (CAT)s, such as L-arginine, L-lysine, and L-ornithine. The expression of CAT1 protein was detected in TR-MUL5 cells. These results suggest that CAT1 is at least involved in [(3)H]l-arginine uptake by TR-MUL5 cells. In conclusion, GlyT1 and CAT1 most likely mediate glycine and L-arginine uptake, respectively, by Müller cells and are expected to play an important role in supplying precursors for creatine biosynthesis in Müller cells.
Hosoya
Ken-ichi
K
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
Ichikawa
Takamichi
T
Akanuma
Shin-ichi
S
Hirose
Shirou
S
Tachikawa
Masanori
M
D026924:Amino Acid Transport System A / Q000235:genetics / Q000378:metabolism; D026905:Amino Acid Transport Systems / Q000235:genetics* / Q000378:metabolism*; D000818:Animals; D001120:Arginine / Q000378:metabolism*; D001693:Biological Transport, Active; D015153:Blotting, Western; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis / Q000235:genetics; D003627:Data Interpretation, Statistical; D004305:Dose-Response Relationship, Drug; D005998:Glycine / Q000378:metabolism*; D050487:Glycine Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D007202:Indicators and Reagents; D007700:Kinetics; D008297:Male; D009457:Neuroglia / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050916:TRPV Cation Channels / Q000235:genetics / Q000378:metabolism
D026924:Amino Acid Transport System A; D026905:Amino Acid Transport Systems; D050487:Glycine Plasma Membrane Transport Proteins; D007202:Indicators and Reagents; C486716:Slc38a1 protein, rat; C412568:Slc38a2 protein, rat; C493266:Slc6a9 protein, rat; D050916:TRPV Cation Channels; C120776:TRPV6 channel; D004247:DNA; D001120:Arginine; D005998:Glycine