The glycine site of the N-methyl-D-aspartate receptor channel: differences between the binding of HA-966 and of 7-chlorokynurenic acid.
The mechanisms of action of three different glycine-site antagonists of the N-methyl-D-aspartate (NMDA)-receptor channel were analyzed employing [3H]glycine direct binding assays, as well as functional glycine- and glutamate-induced uncompetitive blocker binding assays. The latter assays measure apparent channel opening. All three antagonists tested, viz., 7-chlorokynurenic acid (7-Cl-KYNA), kynurenic acid (KYNA), and 1-hydroxy-3-aminopyrrolidone-2 (HA-966), inhibited the binding of [3H]glycine to the NMDA receptor in a dose-dependent manner. These antagonists also inhibited the glycine-induced increase in accessibility of the uncompetitive blocker [3H]N-[1-(2-thienyl)cyclohexyl]-piperidine ([3H]TCP) to the channel. 7-Cl-KYNA and KYNA, but not HA-966, completely blocked the glutamate-induced binding of [3H]TCP, in a manner similar to the non-competitive manner in which the selective NMDA antagonist D-(-)-2-amino-5-phosphonovaleric acid (AP-5) inhibited glycine-induced [3H]TCP binding. The inhibitory effects of HA-966 and of AP-5 on glutamate-induced [3H]TCP binding were overcome when glutamate concentrations were increased. Of the three antagonists, 7-Cl-KYNA appears to be the most potent (Ki = 0.4-1.0 microM) and the most selective glycine antagonist. KYNA was found to act at both the glycine (Ki = 40-50 microM) and the glutamate sites. In contrast, HA-966 (Ki = 6-17 microM) appears to act either on a domain distinct from the glutamate and the glycine sites, but tightly associated with the latter, or at the glycine site, but according to a mechanism distinct from that of 7-Cl-KYNA.(ABSTRACT TRUNCATED AT 250 WORDS)
Kloog
Y
Y
Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel.
Lamdani-Itkin
H
H
Sokolovsky
M
M
D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D005998:Glycine / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism*; D007736:Kynurenic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D010622:Phencyclidine / Q000031:analogs & derivatives / Q000378:metabolism; D011760:Pyrrolidinones / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D013331:Strychnine / Q000494:pharmacology
D007473:Ion Channels; D011760:Pyrrolidinones; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter; C012058:tenocyclidine; C001369:1-hydroxy-3-amino-2-pyrrolidone; D007736:Kynurenic Acid; D013331:Strychnine; D010622:Phencyclidine; C057013:7-chlorokynurenic acid; D005998:Glycine