INTERACTION OF OPIATES WITH OPIOID BINDING-SITES IN THE BOVINE ADRENAL-MEDULLA .2. INTERACTION WITH KAPPA-SITES

The interaction of opiates with .kappa. binding sites in the bovine adrenal medulla was examined. [3H]Ethylketocyclazocine (EKC), [3H]etorphine and [3H]bremazocine stereoselective bindings were used to assay these interactions. The .kappa. sites were found to be heterogeneous: [3H]bremazocine identified with high affinity all subtypes of these sites. [3H]EKC, in the presence of saturating concentrations of [D-Ala2, D-Leu5]-enkephalin (DADLE) (5 .mu.M), was used to identify .kappa.1 sites, on which dynorphin A (1-13) bound with high affinity. Either [3H]EKC or [3H]etorphine in the presence of 5 .mu.M DADLE identified the .kappa.2 subtype. This subtype was found to interact with .beta.-endorphin and especially with the octapeptide Met5-enkephalyl-Arg6-Gly7-Leu8. [3H]etorphine identified in the bovine adrenal medulla and 3rd high-affinity component, in the presence of 5 .mu.M DADLE. This residual interaction was found to be equally stereoselective and presenting .kappa. selectivity. Met5-enkephalyl-Arg6-Phe7 interacted preferentially with this site. The 3 .kappa. subtype interacted differentially with monovalent (Na+, K+, and Li+) and divalent (Ca2+, Mg2+, and Mn2+) ions by modification of the apparent concentration of the accessibe sites and/or by changes of the apparent Kd for radioligands. Modifying agents (proteolytic enzymes, thiol-modifying reagents, and A2-phospholipase) produced different effects on each subtype of the .kappa. site, suggesting a different protein (or protein-lipid?) composition.