Abstract
Binding of dermorphin to the two major opioid receptor types, μ and δ, in rat brain membranes was examined by displacement of [ 3H] [D-Ala 2,MePhe 4,Gly-(ol) 5]enkephalin (DAGO) and [ 3H]-[D-Ala 2,D-Leu 5]-enkephalin (DADLE) binding. Affinity of dermorphin binding to μ sites, K d = 1.24 nM, was almost 3 times greater than that of DAGO, K d = 3.35 nM. In contrast, the K d value of dermorphin binding to δ sites was 78 nM only, as compared to K d = 2.27 nM for DADLE. Dermorphin was ineffective in displacing [ 3H]ethylketocyclazocine (EKC) binding to κ receptors after prior blocking of [ 3H]EKC binding to μ and δ sites. Studies of dermorphin binding to μ sites revealed that the potency of dermorphin increased in the presence of Na + (+31%) but decreased in the presence of Mn 2+ (−81%) or Gpp(NH)p (−44%). Displacement of bound [ 3H]diprenorphine (DPN) by dermorphin from atrial membranes of the rat heart, left side, was detectable, suggesting the presence of μ sites in this section of the heart.
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