PHARMACOLOGICAL CHARACTERIZATION OF THE N-METHYL-D-ASPARTATE (NMDA) RECEPTOR RECOGNITION SITE IN PORCINE CEREBRAL CORTICAL MEMBRANES USING [H-3] CGP-39653

The high-affinity NMDA receptor competitive antagonist [H-3]-CGP 39653 binds to Triton X-100 (0.04%) treated porcine cerebral cortex membranes in a saturable and reversible manner, with a K-D of 6.1 +/- 0.97 nM and a B-max of 944 +/- 55 fmol/mg protein. Association of ligand with the recognition site was rapid (estimated k(1) = 1.1 x 10(7) M(-1) min(-1)), and a steady state was reached within 30 min of incubation at 4 degrees C. Dissociation was also rapid (estimated k(-1) = 0.2 min(-1)). The pharmacology of the binding site was similar to that for the rat brain, with mean pIC(50) values (Hill slopes in parentheses, ''indicating significant difference from unity) of 7.54 (0.51*), 6.99 (0.68*), 6.98 (0.71), 6.63 (0.80*), 6.31 (0.62*) and 5.17 (0.78) for R-CPP, L-glutamate, CGS 19755, cis-2,4-methanoglutamate, L-aspartate and NMDA, respectively. Other compounds (glycine, MK-801, kainate, S-AMPA and magnesium ions), previously observed not to interact competitively with the NMDA binding recognition site, showed a low affinity for the porcine cerebral cortex [H-3]-CGP 39653 binding site. It is concluded that the pharmacological properties of the NMDA receptor recognition site labelled by [H-3]-CGP 39653 are similar in the pig and rat cerebral cortices.