The glycine site modulates NMDA-mediated changes of intracellular free calcium in cultures of hippocampal neurons.
Recent evidence indicates that the N-methyl-D-aspartate (NMDA) receptor-channel complex contains a glycine subunit whose activation may be necessary for channel operation. It has been previously shown that stimulation of the NMDA receptor leads to an increase in intracellular ionic Ca2+ [( Ca2+]i); therefore, we examined the role of the NMDA receptor-associated glycine site in modulating [Ca2+]i using the fluorescent dye Fura II in hippocampal neuron cultures. A 3-s pulse of 200 microM NMDA resulted in a mean [Ca2+]i increase of 363 nM above the average resting concentration of 122 nM. Perfusion of the glycine site antagonist 7-chlorokynurenate (Cl-Kyn) essentially eliminated the NMDA-induced alteration in [Ca2+]i. Either 40 microM glycine or 50 microM D-serine completely reversed the effect of Cl-Kyn, indicating that the drug was acting at the glycine site. The NMDA receptor antagonists 2-amino-5-phosphonovalerate (AP5) and ketamine, which bind to the glutamate recognition site and the ion channel, respectively, also blocked the NMDA-mediated [Ca2+]i response; however, glycine or D-serine did not reverse this effect. These data show that the glycine binding site coupled to the NMDA receptor modulates the NMDA-mediated increase in [Ca2+]i. Antagonists of the glycine site provide a new tool to investigate and possibly control neuroplasticity and neurotoxicity related to the NMDA receptor complex.
Oliver
M W
MW
Center for the Neurobiology of Learning and Memory, Bonney Center, University of California, Irvine 92717.
Shacklock
J A
JA
Kessler
M
M
Lynch
G
G
Baimbridge
K G
KG
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004622:Embryo, Mammalian; D005998:Glycine / Q000494:pharmacology; D006624:Hippocampus / Q000502:physiology*; D007649:Ketamine / Q000494:pharmacology; D007700:Kinetics; D007736:Kynurenic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D046911:Macromolecular Substances; D016202:N-Methylaspartate; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D018009:Receptors, Glycine; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter / Q000502:physiology*; D012694:Serine / Q000494:pharmacology
D046911:Macromolecular Substances; D018009:Receptors, Glycine; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter; D001224:Aspartic Acid; D012694:Serine; D016202:N-Methylaspartate; D007649:Ketamine; D015763:2-Amino-5-phosphonovalerate; D007736:Kynurenic Acid; C057013:7-chlorokynurenic acid; D002118:Calcium; D005998:Glycine