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Mugnaini M, Antolini M, Corsi M, van Amsterdam FT: [3H] 5,7-dichlorokynurenic acid recognizes two binding sites in rat cerebral cortex membranes. J Recept Signal Transduct Res. 1998 Mar-May;18(2-3):91-112.
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. |
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