Cell-specific expression of N-methyl-D-aspartate receptor subunits in Müller glia and neurons from the chick retina.
OBJECTIVE
Functional N-methyl-D-aspartate (NMDA) receptors (NMDARs) in Müller glia may influence glutamate neurotransmission through feedback loops between glia and neurons. The physiologic properties of NMDARs derive from the subunit composition of the tetrameric receptor. We characterized glycine binding to the NMDAR coagonist site in Müller cell membranes and determined NMDAR subunit expression in chick Müller glia compared with retinal neurons to make predictions about the heteromeric assembly of NMDARs.


METHODS
Kinetic and pharmacologic properties of the glycine coagonist site were determined by radiolabeled ligand binding to membrane preparations from chick Müller glia and retinal neurons in primary culture. The molecular composition of NMDARs was analyzed by RT-PCR amplification and Western blotting.


RESULTS
The NMDAR coagonist site in Müller cell membranes has 5-fold lower affinity for glycine and 30-fold lower affinity for D-serine compared with values obtained for synaptic membranes from whole retina and with reported values in brain tissue. NR1 subunit N-terminal and C-terminal splice-variant expression also differs in Müller cells and retinal neurons.


CONCLUSIONS
Pharmacologic characteristics of NMDAR coagonist-site differ in Müller glia and neurons from the retina, in agreement with the distinct subunit expression profile found. Whereas NMDARs in Müller glia contain exclusively exon 5 that lacks NR1 subunits, receptors in distinct subtypes of neurons may contain NR1 with or without exon 5, suggesting a cell-specific assembly of the NMDAR complex. Structural differences in NMDARs could underlie the differential participation of neurons and glia in the physiologic control of glutamate transmission in the retina.
Lamas
Mónica
M
Instituto de Fisiología Celular, Departamento de Neurociencias, Universidad Nacional Autónoma de México (UNAM).
Lee-Rivera
Irene
I
López-Colomé
Ana María
AM
D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D002642:Chick Embryo; D005998:Glycine / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D007736:Kynurenic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D009457:Neuroglia / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D011869:Radioligand Assay; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D012160:Retina / Q000196:embryology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012694:Serine / Q000378:metabolism; D013096:Spermine / Q000494:pharmacology; D013570:Synaptic Membranes / Q000187:drug effects / Q000378:metabolism
D007527:Isoenzymes; D016194:Receptors, N-Methyl-D-Aspartate; D013096:Spermine; D012694:Serine; D007736:Kynurenic Acid; C057013:7-chlorokynurenic acid; D005998:Glycine