Parallel inactivation of α2‐adrenergic agonist binding and Ni by alkaline treatment

Abstract

α₂-Adrenergic receptor-mediated inhibition of adenylate cyclase requires the guanine nucleotide-binding protein, N_i. This protein may also be required for stabilization of high-affinity α₂-adrenergic agonist binding. Human platelet membranes treated under alkaline conditions (pH 11.5) exhibited a selective loss of high-affinity agonist binding as measured by P-[³H]aminoclonidine and [³H]UK 14,304. Binding of the antagonist [³H]yohimbine was largely unaffected with retention of > 60% of control binding sites. N_i determined by pertussis toxin-catalyzed [³²P]ADP-ribosylation of cholate extracts from alkaline-treated membranes, was also markedly reduced. The parallel loss of of α₂-agonist binding and N_i provides additional evidence that N_i, is required for α₂-adrenergic agonist binding.