Abstract
Neurochemical studies have indicated that the dissociative anesthetics, phencyclidine (PCP) and ketamine, act as non-competitive antagonists at the excitatory amino acid, N-methyl-D-aspartate (NMDA), receptor-gated ion channel. Since the binding of PCP and related psychotomimetics, i.e. (+)-N-allylnormetazocine [+)-SKF 10047), in mammalian brain is associated with multiple receptor subtypes, their modulation by NMDA agonists and antagonists was investigated. Binding of the potent PCP analog, [3H]PCP-3-OH to the high-affinity sigma/PCP (sigma p) site and (+)-[3H]SKF 10047 to the sigma/haloperidol sensitive (sigma h) site in rat brain membranes was not affected by L-glutamate and NMDA, nor by the competitive NMDA antagonists D-2-amino-5-phosphovaleric acid (AP-5), D-2-amino-7-phosphoheptanoic acid (AP-7). However, binding of [3H]PCP-3-OH to the low-affinity PCP-selective site was enhanced by 4- to 5-fold in the presence of glutamate or NMDA and reduced in a competitive manner by AP-5. The noncompetitive NMDA antagonist, MK-801, was however a potent inhibitor of the binding to both sigma p and PCP sites labeled with [3H]PCP-3-OH. The present results indicate that the high (sigma p) and low-affinity (PCP) sites, that are distinct from the sigma h site, are affected differently by NMDA agonists and antagonists, and thus may represent different receptor domains.
