Characterisation of opioid receptor binding in guinea-pig cerebellum

The binding of the non-selective opioid receptor ligand [3H]bremazocine to guinea-pig cerebellum membranes in HEPES buffer was found to be selective for the opioid kappa receptor, as defined in the literature. However, displacement curves to dynorphin A (1-17) and a number of other peptides, suggested the presence of a "dynorphin resistant" binding site, comprising 15¬–20% of the specific binding. This component was not abolished by high concentrations of the mu/delta selective ligand [D-Ala2,D-Leu5]enkephalin, suggesting the presence of an additional binding-site, labelled by [3H]bremazocine, that could not be defined as high affinity mu, delta or kappa. [Continues.]