The human platelet vasopressin receptor and its intracellular messengers: key role of divalent cations.

The effects of divalent cations on human platelet vasopressin receptor binding characteristics and effects of receptor occupancy on endogenous protein phosphorylation were investigated. Binding of vasopressin to its receptor is modulated by both the nature and the concentration of ions. Whatever the cation present, guanosine 5'-triphosphate or 5' guanylylimidodiphosphate do not alter the receptor binding characteristics. In the presence of extracellular calcium, vasopressin stimulates the phosphorylation of a 45,000-dalton protein and to a lesser degree of a 20,000-dalton protein following a pattern observed with thrombin and 12-O-tetradecanoylphorbol-13-acetate, a phorbol ester. Phosphorylation is also stimulated by a V1 vascular agonist, but not V2 renal agonists, and is more potently blocked by a V1 vascular antagonist than by a V2 renal antagonist. These results suggest that human platelets bear typical V1 vascular vasopressin receptors which stimulate the phosphorylation of specific substrates of protein kinase C and myosin light-chain kinase.