Altered opiate receptor binding in synaptosomes: Implication of phosphorylation

There is thus strong evidence that exposure to phosphorylating conditions resulted in demonstrable stimulation of DADLE binding but not of dihydromorphine or EKC binding. The effect occurred at a concentration far below the reported high affinity K(d) for DADLE of 1.9 nM (9). Biochemical processes have been demonstrated to be in operation during the various experimental procedures, and these would alter the phosphorylated state of the synaptosome. The observed results were thus the product of a balance between opposing processes. The observation that both the substrate and the co-factor were required in the preincubation to achieve stimulation of DADLE binding activity supported the implication that this was due to an enzymatically mediated process. Phosphorylation regulated opiate receptor binding thus remains an attractive model for a mechanism of opiate action. Better understanding of the functional differences of the sites which bind the various classes of opiates might illuminate the significance of the observation that only DADLE binding was affected.