OPIOID PEPTIDE RECEPTOR STUDIES - 9 - IDENTIFICATION OF A NOVEL NON-MU-LIKE NON-DELTA-LIKE OPIOID PEPTIDE BINDING-SITE IN RAT-BRAIN

Quantitative binding studies resolved two high-affinity [H-3] [D-Ala(2 ), D-Leu(5)]enkephalin binding sites in rat brain membranes depleted o f mu, binding sites by pretreatment with the irreversible agent BIT. - The two binding sites had lower (delta(ncx-2), Ki = 96.6 nM) and highe r (delta(ncx-1), Ki = 1.55 nM) affinity for DPDPE. The ligand-selectiv ity profile of the delta(ncx-1), site was that of a classic delta bind ing site. The ligand-selectivity profile of the delta(ncx-2) site was neither mu- or delta-like. The Ki values of selected agents for the de lta(ncx-2), site were: [pCl]DPDPE (3.9 nM), DPLPE (140 nhl), and DAMGO (2.6 nM). Under these assay conditions, [H-3]CD-Ala(2),D-Leu(5)]enkep halin binding to the cells expressing the cloned CL receptor is very l ow and pretreatment of cell membranes with BIT almost completely inhib its [H-3]DAMGO and [H-3][D-Ala(2),D-Leu(5)]enkephalin binding. Intrace rebroventricular administration of antisense DNA to the cloned delta r eceptor selectively decreased [H-3][D-Ala2,D-Leu5]enkephalin binding t o the delta(ncx-1) site. Administration of buprenorphine to rats 24 h prior to preparation of membranes differentially affected mu, delta(nc x-1), and delta(ncx-2), binding sites. Viewed collectively, these stud ies have identified a novel non-mu- non-delta-like binding site in rat brain. (C) 1998 Elsevier Science Inc.