Binding characteristics of the novel highly selective delta agonist, [ 3H]Ile 5,6deltorphin II

Abstract

Following the description of the [ 3H]deltorphin II, it has been reported that the modification of deltorphin II with the substitution of Val 5,6 residues by the more hydrophobic lle 5,6 residues leads to an increased affinity and selectivity. The lle 5,6deltorphin II (Tyr-D-Ala-Phe-Gly-lle-lle-Gly-NH 2) was tritiated by catalytic dehalogenation and labelled rat brain membrane sites with a K d value of 0.40 nM and a B max of 121 fmol/mg protein. Competition binding experiments with various unlabelled subtype specific opioid receptor ligands resulted in μ δ and κ δ selectivity ratios of 2400 and 18 000 respectively. Due to its high δ receptor affinity, δ selectivity and very low non-specific binding (<20%), [ 3H]lle 5,6deltorphin II, is a very useful tool for the identification and characterisation of δ opioid receptors.