Solubilization of Rat Brain Phencyclidine Receptors in an Active Binding Form That Is Sensitive to N‐Methyl‐d‐Aspartate Receptor Ligands

Phencyclidine (PCP) receptors were successfully solubilized from rat forebrain membranes with 1% sodium cholate. Approximately 58% of the initial protein and 20–30% of the high‐affinity PCP binding sites were solubilized. The high affinity toward PCP‐like drugs, the stereo‐selectivity of the sites, and the sensitivity to N‐methyl‐d‐aspartate (NMDA) receptor ligands were preserved. Binding of the potent PCP receptor ligand N‐[³H][l‐(2‐thienyl)cyclohexyl] piperidine ([³H]TCP) to the soluble receptors was saturable (K_D= 35 nM), and PCP‐like drugs inhibited [³H]TCP binding in a rank order of potency close to that observed for the membrane‐bound receptors; the most potent inhibitors were TCP (K_i= 31 nM) and the anticonvulsant MK‐801 (K_i= 50 nM). The NMDA receptor antagonist 2‐amino‐5‐phosphonovaleric acid inhibited‐binding of [³H]TCP to the soluble receptors; glutamate or NMDA diminished this inhibition in a dose‐dependent manner. Taken together, the results indicate that the soluble PCP receptor preparation contains the glutamate recognition sites and may represent a single receptor complex for PCP and NMDA, as suggested by electrophysiological data. The successful solubilization of the PCP receptors in an active binding form should now facilitate their purification.