Pseudoallosteric modulation by (+)-MK801 of NMDA-coupled phencyclidine binding sites.

Two high affinity phencyclidine (PCP) binding sites, labelled by [3H] 1-[1-(2-thienyl)cyclohexyl]piperidine ([3H]TCP), have been identified in guinea pig brain, with one site coupled to the N-methyl-D-aspartate (NMDA) receptor (site 1) and the other site associated with the dopamine reuptake carrier complex (site 2). In this study, PCP enhanced the dissociation of [3H]TCP from PCP site 1 and site 2, while (+)-MK801 only enhanced dissociation of [3H]TCP from PCP site 1. Although additional studies will be required to determine the exact mechanism(s) of these effects, these data demonstrate that the interactions of PCP with both site 1 and site 2 are more complex than previously appreciated.