The platelet activation induced by wheat germ agglutinin.

In human platelets, wheat germ agglutinin (WGA) induced serotonin release without cell agglutination. WGA induced the phosphorylation of both 40-kDa and 20-kDa proteins in a parallel manner, and at least, the phosphorylation of 40-kDa protein was preceded by transient formation of endogenous diacylglycerol (DG) accompanied by a decrease in phosphatidylinositol (PI). Both phosphorylation of these two proteins and serotonin release were inhibited by prior treatment of platelets with dibutyryl cyclic AMP, W-7, or TMB-8. These results suggest that both phosphatidylinositol turnover and Ca2+ mobilization play an essential role in WGA-induced platelet activation.