VASOPRESSIN DEPENDENT TYROSINE PHOSPHORYLATION OF A 38 KDA PROTEIN IN HUMAN PLATELETS

Arginine vasopressin administration (10-10-10-6 M) to isolated human platelets induces an increase in the specific immunoblotting of a 38 kDa protein revealed by a phosphotyrosine antibody. This signal is biphasic with maximal stimulation within one minute. Neither forskolin (10-5 M) nor phorbol ester (10-6 M) produces a similar 38 kDa signal. The specific immunoblotted signals are competitively abolished by 1 mM phosphotyrosine but not phosphoserine or phosphothreonine. Electrophoretic separation at pH 3.5 of the acid hydrolysates of the 38 kDa proteins reveals a vasopressin dependent increase in levels of phosphotyrosine as well as phosphoserine and phosphothreonine. The 38 kDa phosphorylation is also induced by the specific arginine vasopressin V1 receptor agonist (Phe2Orn8Vastocina) and blocked by the V1 receptor antagonist [desGly(NH2d(CH2)5Tyr(Me) AVPb]. These observations suggest that arginine vasopressin signal transduction may be associated with the tyrosine phosphorylation of a 38 kDa protein. © 1990.