Selective alterations in guanine nucleotide regulation of opiate receptor binding and coupling with adenylate cyclase

Pretreatment of rat brain membranes at pH 4.5 increased GTP and Gpp(NH)p regulation of [3H]-D-ala2-met5-enkephalinamide (D-ala-enk) binding with no change in absolute binding itself. Pretreatment at pH 4.5 did not alter basal adenylate cyclase activity but did cause a loss (50-90%) in NaF- and Gpp(NH)p-stimulated activity, indicating a functional loss of GTP-coupling proteins. The addition of cis-vaccenic acid partially restored NaF- and Gpp(NH)p-stimulated cyclase after low pH pretreatment but, in the same membranes, did not reverse the increase in GTP regulation of agonist binding. These results suggest that GTP regulation of binding and stimulation of adenylate cyclase occur by fundamentally different mechanisms.