DIFFERENTIATION OF GLYCINE ANTAGONIST SITES OF N-METHYL-D-ASPARTATE RECEPTOR SUBTYPES - PREFERENTIAL INTERACTION OF CGP-61594 WITH NR1 2B RECEPTORS/

The binding site for the co-agonist glycine on N-methyl-D-aspartate (N MDA) receptors has been mapped to the NR1 subunit whereas binding of t he principal agonist glutamate is mediated by the NR2 subunits, Using the novel glycine site antagonist and photoaffinity label CGP 61594, d istinct contributions of the NR2 subunit variants to the glycine antag onist binding domains of NMDA receptor subtypes are demonstrated. High affinity sites for CGP 61594 were exclusively displayed by NR1/2B rec eptors, as shown by their co-distribution with the NR2B subunit, by su bunit-selective immunoprecipitation and by functional analysis of NR1/ 2B receptors expressed in Xenopus oocytes (inhibitory potency, IC50 = 45 +/- 11 nM). Other NMDA receptor subtypes are clearly distinguished by reduced inhibitory potencies for CGP 61594, being low for NR1/2A an d NR1/2D receptors (IC50 = 430 +/- 105 nm and 340 +/- 61 nM, respectiv ely) and intermediate for NR1/2C receptors (IC50 = 164 +/- 27 nM). Gly cine antagonist sites with low and intermediate affinity for [H-3]CGP 61594 were detected also in situ by radioligand binding in brain areas predominantly expressing the NR2A and NR2C subunits, respectively. Th us, [H-3]CGP 61594 is the first antagonist radioligand that reliably d istinguishes the gig-cine site of NMDA receptor subtypes. [H-3]CGP 615 94 is a promising tool to identify the NR2 subunit domains that contri bute to differential glycine antagonist sites of NMDA receptor subtype s.