Preparation of rat brain membranes greatly enriched with either type-I-delta or type-II-delta opiate binding sites using site directed alkylating agents: Evidence for a two-site allosteric model

Although it is widely accepted that radiolabeled prototypic delta receptor agonists label two binding sites in vitro, the mechanism by which mu ligands inhibit peptide binding as well as the identity of the binding sites remains unsettled (Rothman and Westfall, Mol. Pharmacol. 21:538–547, 1982; Bowen et al., Proc. Natl. Acad. Sci. U.S.A. 78:4818–4822, 1981). Using the site directed, receptor selective alkylating agents, BIT and FIT (Rice et al., Science 220:314–316, 1983), we describe the preparation of membranes devoid of high affinity binding sites and demonstrate that the mu agonist oxymorphone noncompetitively inhibits the binding of [3H]DADL to the residual lower affinity binding sites.