Regional heterogeneity of rat brain phencyclidine (PCP) receptors revealed by photoaffinity labeling with [3H] azido phencyclidine

Photoaffinity labeling and binding studies reveal the existence of two types of phencyclidine receptors in the NCB-20 cell line

The mouse neuroblastoma-Chinese hamster brain hybrid cell line NCB-20 is the only clonal cell line in which binding studies indicate the presence of phencyclidine (PCP) receptor-like sites. We report here that polypeptide components of NCB-20 cell PCP sites were identified with the photolabile PCP derivative [3H]N-[1-(3-azidophenyl)cyclohexyl]piperidine ([3H]AZ-PCP). The pharmacological selectivity of [3H]AZ-PCP binding (under reversible conditions) was similar to that observed for [3H]N-[1-(2-thienyl)cyclohexyl]piperidine ([3H]TCP) binding to NCB-20 cell membranes. Inhibition of [3H]TCP binding by AZ-PCP, dexoxadrol or MK-801 was biphasic, suggesting the presence of two types of PCP sites on NCB-20 cells. Photolysis of NCB-20 cell membranes pre-equilibrated with [3H]AZ-PCP, followed by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), revealed the presence of 5 major labeled bands (Mr 90,000, 68,000, 49,000, 40,000 and 33,000), a pattern similar to that observed for rat brain membranes. MK-801 and D-2-amino-5-phosphonovaleric acid (D-(-)-AP5) selectively inhibited the labeling of Mr 68,000 and 90,000 polypeptides. These results indicate that the labeled bands represent constituents of at least two different PCP binding proteins. The Mr 68,000 and 90,000 components appear to correspond to a high-affinity site, which comprises approximately 20% of total [3H]TCP sites in these cells, and exhibits the pharmacology expected for the PCP receptor of the N-methyl-D-aspartate (NMDA)-gated channel.

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][1-(2-thienyl)cyclohexyl] piperidine ([3H]TCP) to the soluble receptors was saturable (KD = 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 (Ki = 31 nM) and the anticonvulsant MK-801 (Ki = 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.

Binding studies and photoaffinity labeling identify two classes of phencyclidine receptors in rat brain

Binding and photoaffinity labeling experiments were employed in order to differentiate 1-(1-phenylcyclohexyl)piperidine (PCP) receptor sites in rat brain. Two classes of PCP receptors were characterized and localized: one class binds [3H]-N-[1-(2-thienyl)cyclohexyl]piperidine [( 3H]TCP) with high affinity (Kd = 10-15 nM) and the other binds the ligand with a relatively low affinity (Kd = 80-100 nM). The two classes of sites have different patterns of distribution. Forebrain regions are characterized by high-affinity sites (hippocampus greater than frontal cortex greater than thalamus greater than olfactory bulb greater than hypothalamus), but some parts (e.g., hippocampus, hypothalamus) contain low-affinity sites as well. In the cerebellum only low-affinity sites were detected. Binding sites for [3H]PCP and for its photolabile analogue [3H]azido-PCP showed a regional distribution similar to that of the [3H]TCP sites. The neuroleptic drug haloperidol did not block binding to either the high- or the low-affinity [3H]TCP sites, whereas Ca2+ inhibited binding to both. Photoaffinity labeling of the PCP receptors with [3H]AZ-PCP indicated that five specifically labeled polypeptides of these receptors (Mr 90,000, 62,000, 49,000, 40,000, and 33,000) are unevenly distributed in the rat brain. Two of the stereoselectively labeled polypeptides (Mr 90,000 and 33,000) appear to be associated with the high- and low-affinity [3H]TCP-binding sites; the density of the Mr 90,000 polypeptide in various brain regions correlates well with the localization of the high-affinity sites, whereas the density of the Mr 33,000 polypeptide correlates best with the distribution of the low-affinity sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple mode of binding of phencyclidines: high affinity association between phencyclidine receptors in rat brain and a monovalent ion-sensitive polypeptide

Two populations of phencyclidine (PCP) binding sites are shown to exist in the rat brain: a high-affinity monovalent ion-sensitive site (Kd of 10-14 nM for [3H]TCP, [3H]N-[1-(2-thienyl)cyclohexyl]piperidine), which exists in both the frontal cortex and the hippocampus, and a lower affinity site (Kd of 80-130 nM for [3H]TCP) which is found in the hippocampus but not in the frontal cortex. The nature of the interactions between the ion-binding sites and the high affinity PCP receptors depend on both ligand structure (PCP or TCP) and the ion involved (K' or Na'). The high-affinity sites are associated with an Mr 90,000 polypeptide whose labeling by [3H]azido phencyclidine is selectively inhibited by monovalent ions.

Acylating phencyclidines irreversibly enhance brain calcium antagonist binding

Phencyclidine was previously shown to allosterically increase the apparent affinity of the dihydropyridine ( [3H]nitrendipine) calcium antagonist binding site in a lysed synaptosomal membrane preparation of rat forebrain. Treatment of a similar preparation of mouse forebrain with 4-isothiocyanato-1-(1-phenylcyclohexyl) piperidine (FOURPHIT), an acylating phencyclidine derivative, resulted in a concentration dependent (0.1-10 microM), irreversible, increase in the apparent affinity of [3H]nitrendipine in contrast to the effects of phencyclidine which were reversible. The FOURPHIT isomer, 1-[1-(3-isothiocyanatophenyl) cyclohexyl] piperidine (METAPHIT), (10 microM) also irreversibly increased the apparent affinity of [3H]nitrendipine, but was much less efficacious than FOURPHIT. Phencyclidine blocked the irreversible increase in the apparent affinity of [3H]nitrendipine produced by FOURPHIT. The interactions of multivalent cations and the calcium antagonist diltiazem with the [3H]nitrendipine binding site were altered following treatment of membranes with FOURPHIT. These studies suggest that FOURPHIT irreversibly interacts with the same sites as PCP, and thus may be a useful tool with which to further probe both the behavioral and biochemical interactions between phencyclidine and the dihydropyridine calcium antagonist binding site.