Effects of A23187 on platelet aggregation and protein phosphorylation.

To study further the role of Ca2+ and protein kinase C in platelet aggregation, suspensions of aspirin-treated, P-32-prelabled, washed pig platelets containing ABP scavenger in the buffer were stimulated by Ca2+ ionophore A23187 and PMA, a stimulator of protein kinase C. The results indicated that: (1) 1 similar to 20 mu mol/L A23187 induced platelet aggregation, as well as the phosphorylation of 40 ku and 20 ku proteins. There were dose-respone and time-respone effects of the protein phosphorylation in A23187-induced platelet activation. (2) A23187 and PMA were synergistic in platelet aggregation and protein phosphorylation. (3) Stauroporine, a protein kinase C inhibitor, in concentration of 1 mu mol/L, largely suppressed platelet aggregation and completely suppressed phosphorylation of 40 ku and 20 ku proteins induced by 20 mu mol/L A23187. The results imply that Ca2+ mobilization alone could activate protein kinase C in platelet, and Ca2+ induced platelet aggregation is largely dependent on activation of protein kinase C.