Relationship between intracellular calcium-dependent process and protein-tyrosine phosphorylation in human platelets: studies of platelets from a patient with defective A23187-induced platelet aggregation

We had postulated that in a patient with defective calcium ionophore (A2318 7)-induced platelet aggregation, whose platelets showed normal intracellula r Ca2+ mobilization in either the presence or absence of extracellular Ca2 in response to A23187. A defect was present in an intracellular calcium-de pendent process. We have now investigated whether the agonist-induced prote in-tyrosine phosphorylation (PTP) was altered. Protein-tyrosine phosphoryla tion (PTP)-induced by,A23187 in the patient's platelets was greatly diminis hed but that induced by thrombin was almost normal. These results suggest t hat an intracellular calcium-dependent process plays a fundamental role in A23187-induced PTP, whereas it does not in thrombin -induced PTP.