Opioid binding properties in bovine retina

Saturable binding sites for tritiated dihydromorphine ([(3)H]DHM), D-Ala(2)-D-Leu(5)-enkephalin ([(3)H]DADL) and etorphine were found in a crude synaptosomal preparation of bovine retina. Scatchard analysis of saturation binding curves of each ligand was curvilinear and the presence of two independent binding sites inferred. The density of binding sites of [(3)H]etorphine was similar to that reported in brain crude synaptosomal preparations, and the affinity for the high affinity binding site to each ligand was similar to values determined in brain. Moreover, the regulation of the binding sites by GTP and sodium was also similar to that observed in brain. Selective binding sites for [(3)H]DADL (?-sites) were not detectable, although binding sites similar in nature to ?-binding sites were detected.