[3H]5,7-dichlorokynurenic acid recognizes two binding sites in rat cerebral cortex membranes.
Binding of [3H]5,7-dichlorokynurenic acid ([3H]DCKA), a competitive antagonist of the strychnine-insensitive glycine site of the N-methyl-D-aspartate (NMDA) receptor channel complex, was characterized in synaptic plasma membranes from rat cerebral cortex. Non linear curve fitting of [3H]DCKA saturation and homologous displacement isotherms indicated the existence of two binding sites: a specific, saturable, high affinity site, with a pKD value of 7.24 (KD = 57.5 nmol/l) and a maximum binding value (Bmax) of 6.9 pmol/mg of protein and a second site, with micromolar affinity. The pharmacological profile of both binding components was determined by studying the effect on [3H]DCKA and [3H]glycine binding of a series of compounds known to interact with different excitatory and inhibitory amino acid receptors. These studies confirmed the identity of the high affinity site of [3H]DCKA binding with the strychnine-insensitive glycine site of the NMDA receptor channel complex. 3-[2-(Phenylaminocarbonyl)ethenyl]-4,6-dichloroindole-2-carb oxylic acid sodium salt (GV 150526A), a new, high affinity, selective glycine site antagonist (1), was the most potent inhibitor of this component of binding (pKi = 8.24, Ki = 5.6 nmol/l). The low affinity component of [3H]DCKA binding was insensitive to the agonists glycine and D-serine and the partial agonist (+/-)-3-amino-1-hydroxy-2-pyrrolidone (HA 966), though recognised by glycine site antagonists. The precise nature of this second, low affinity [3H]DCKA binding site remains to be elucidated.
Mugnaini
M
M
Glaxo Wellcome S.p.A., Medicines Research Centre, Verona, Italy.
Antolini
M
M
Corsi
M
M
van Amsterdam
F T
FT
D000818:Animals; D001667:Binding, Competitive; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000378:metabolism* / Q000494:pharmacology; D018684:Glycine Agents / Q000378:metabolism / Q000494:pharmacology; D066298:In Vitro Techniques; D007211:Indoles / Q000378:metabolism; D007736:Kynurenic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D018009:Receptors, Glycine / Q000187:drug effects / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013331:Strychnine / Q000378:metabolism / Q000494:pharmacology; D013570:Synaptic Membranes / Q000187:drug effects / Q000378:metabolism
C105319:3-(2-((phenylamino)carbonyl)ethenyl)-4,6-dichloroindole-2-carboxylic acid; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D018684:Glycine Agents; D007211:Indoles; D018009:Receptors, Glycine; D016194:Receptors, N-Methyl-D-Aspartate; D007736:Kynurenic Acid; D013331:Strychnine; C066192:5,7-dichlorokynurenic acid