Species and age-dependent differences of functional coupling between opioid δ-receptor and G-proteins and possible involvement of protein kinase C in striatal membranes

Abstract

[ d-Ser 2,Leu 5]-enkephalin-Thr 6 (DSLET) and [ d-Pen 2,5]-enkephalin (DPDPE), both δ-agonists, stimulated the high affinity GTPase in the rat striatal membranes in a naltrindole-reversible manner. Similar stimulation was also observed in the striatal membrane preparations of 16-week-old guinea pigs, while not in those preparations of 4-week-old ones. When calphostin C, a protein kinase C inhibitor, was added to the reaction mixture, DSLET showed a marked stimulation in this activity in 4-week guinea pig striatal membranes. There was no effect of KT5720, a cyclic AMP-dependent protein kinase inhibitor, on such δ-opioid-mediated responses. These findings suggest that protein kinase C is locally involved in the functional uncoupling of δ-receptors to G-proteins in the striatum of young guinea pigs.