NMDA receptor antagonists that bind to the strychnine-insensitive glycine site and inhibit NMDA-induced Ca2+ fluxes and [3H]GABA release.
We have examined the actions of putative antagonists of the strychnine-insensitive glycine-mediated modulation of the N-methyl-D-aspartate (NMDA) receptor using [3H]MK801 binding, Ca2+ influx and [3H]GABA release assays. Kynurenic acid and HA-966 inhibited [3H]MK801 binding, NMDA and glycine induced Ca2+ influx measured using fura-2 and NMDA and glycine simulated [3H]GABA release. The effects of kynurenic acid could be partially overcome by the addition of excess glutamate and glycine, indicating limited selectivity for the glycine binding site. In addition, a component of the action of kynurenic acid was insensitive to agonist concentration, indicating a third action of kynurenic acid at high concentrations. In contrast, HA-966 was 100-fold selective for the glycine compared to the NMDA site. HA-966 only partially inhibited [3H]MK801 binding (IC50 19.7 microM), NMDA-induced Ca2+ influx and neurotransmitter release. The failure of HA-966 to completely block NMDA responses, even at high concentrations, suggests that glycine may not be an absolute requirement for the activation of NMDA receptors under these experimental conditions.
Reynolds
I J
IJ
Department of Pharmacological and Physiological Sciences, University of Chicago, IL 60637.
Harris
K M
KM
Miller
R J
RJ
D000818:Animals; D000927:Anticonvulsants / Q000378:metabolism; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D003891:Desipramine / Q000494:pharmacology; D003986:Dibenzocycloheptenes / Q000378:metabolism; D016291:Dizocilpine Maleate; D007649:Ketamine / Q000494:pharmacology; D007737:Kynurenine / Q000494:pharmacology; D008566:Membranes / Q000378:metabolism; D016202:N-Methylaspartate; D010879:Piperazines / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D018009:Receptors, Glycine; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D013331:Strychnine / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D000927:Anticonvulsants; D003986:Dibenzocycloheptenes; D010879:Piperazines; D011760:Pyrrolidinones; D018009:Receptors, Glycine; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter; D001224:Aspartic Acid; D007737:Kynurenine; D005680:gamma-Aminobutyric Acid; D016202:N-Methylaspartate; D007649:Ketamine; D016291:Dizocilpine Maleate; C001369:1-hydroxy-3-amino-2-pyrrolidone; D013331:Strychnine; C015068:1-(3-chlorophenyl)piperazine; D002118:Calcium; D003891:Desipramine