TY - JOUR
T1 - Glycine and L-arginine transport in cultured Müller glial cells (TR-MUL)
AU - Hosoya, Ken Ichi
AU - Ichikawa, Takamichi
AU - Akanuma, Shin Ichi
AU - Hirose, Shirou
AU - Tachikawa, Masanori
N1 - Funding Information:
This study was supported, in part, by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS) .
PY - 2010/10
Y1 - 2010/10
N2 - 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, [14C]glycine and [3H]l-arginine uptake by Müller cells was characterized using a conditionally immortalized rat Müller cell line (TR-MUL5 cells). [14C]Glycine uptake by TR-MUL5 cells was Na+- and Cl--dependent, and a saturable process with Michaelis-Menten constants of 48.6μM and 4.53mM, 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 [14C]glycine uptake for the high- and low-affinity processes, respectively, in TR-MUL5 cells. [3H]l-Arginine uptake by TR-MUL5 cells was primarily an Na+-independent and saturable process with Michaelis-Menten constants of 15.0 and 403μM. 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 [3H]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.
AB - 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, [14C]glycine and [3H]l-arginine uptake by Müller cells was characterized using a conditionally immortalized rat Müller cell line (TR-MUL5 cells). [14C]Glycine uptake by TR-MUL5 cells was Na+- and Cl--dependent, and a saturable process with Michaelis-Menten constants of 48.6μM and 4.53mM, 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 [14C]glycine uptake for the high- and low-affinity processes, respectively, in TR-MUL5 cells. [3H]l-Arginine uptake by TR-MUL5 cells was primarily an Na+-independent and saturable process with Michaelis-Menten constants of 15.0 and 403μM. 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 [3H]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.
KW - CAT1
KW - GlyT1
KW - Glycine
KW - L-Arginine
KW - Müller cells
KW - System A
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U2 - 10.1016/j.neuint.2010.06.004
DO - 10.1016/j.neuint.2010.06.004
M3 - Article
C2 - 20558222
AN - SCOPUS:77955095993
VL - 57
SP - 262
EP - 268
JO - Neurochemistry International
JF - Neurochemistry International
SN - 0197-0186
IS - 3
ER -