SITE-DIRECTED ALKYLATION OF MULTIPLE OPIOID RECEPTORS .1. BINDING SELECTIVITY

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  • 1 January 1984
    • journal article
    • research article
    • Vol. 25  (3) , 337-342
Abstract
A method for measuring and expressing the binding selectivity of ligands for .mu., .delta. and .kappa. opioid binding sites is reported. Radioligands that are partially selective for these sites were used in combination with membrane preparations enriched in each site. Enrichment was obtained by treatment of [guinea pig brain] membranes with the alkylating agent .beta.-chlornaltrexamine in the presence of appropriate protecting ligands, sufentanil for .mu. sites [D-Ala2, D-Leu5] enkephalin for .delta. sites and dynorphin A for .kappa. sites. After enrichment for .mu. receptors, [3H]dihydromorphine bound to a single type of site as judged by the slope of competition binding curves. After enrichment for .delta. or .kappa. receptors, binding sites for [3H][D-Ala2,D-Leu5]enkephalin and [3H]ethylketocyclazocine, respectively, were still not homogeneous. There were residual .mu. sites in .delta.-enriched membranes but no evidence for residual .mu. or .delta. sites was found in .kappa.-enriched membranes. This method was used to identify ligands that are highly selective for each of the 3 types of sites: Tyr-D-Ala-Gly-(Me)Phe-Gly-ol, sufentanil and morphiceptin for .mu. sites; (D-Pen2, D-Pen5]enkephalin and [D-Pen2,L-Pen5]enkephalin for .delta. sites; and tifluadom and U50488 [trans-3,4-dichloro-N-methyl-N-[.alpha.-(1-pyrrolidinyl)cyclohexyl-1-]benzeneacetamide] for .kappa. sites.