IONOMYCIN-STIMULATED ARACHIDONIC-ACID RELEASE IN HUMAN PLATELETS - A ROLE FOR PROTEIN-KINASE-C AND TYROSINE PHOSPHORYLATION

Collagen (10-90 mu g/ml) and ionomycin (1 mu M; a calcium ionophore) e ach evoked rises in intracellular free calcium, protein kinase C activ ity and arachidonic acid release in human platelets, and as previously demonstrated for collagen, ionomycin (1 mu M) stimulated protein tyro sine phosphorylation. However, at lower concentrations (60 and 250 nM) ionomycin selectively mobilised calcium. Ro31-8220 (a selective inhib itor of protein kinase C) inhibited (by 50%) ionomycin-stimulated arac hidonic acid release. Genistein (an inhibitor of protein tyrosine kina ses) also reduced by 50% ionomycin-stimulated arachidonic acid release . In combination, genistein and Ro31-8220 abolished ionomycin-stimulat ed arachidonic acid release. These findings show 1) that a rise in cal cium is not sufficient, and 2) the activation of both protein kinase C and protein tyrosine phosphorylation is necessary, for full ionomycin -stimulated arachidonic acid release in human platelets.