Inhibition of phosphatidic acid production and lysophospholipid formation in collagen-stimulated human platelets by staurosporine, a protein kinase inhibitor

To investigate a possible regulatory role of protein kinase C (PKC) on collagen-induced phospholipase activity, human platelets were prelabelled with either [3H] arachidonic acid or [14C]stearic acid and stimulated with collagen (2 micrograms/ml) in the presence or absence of the protein kinase inhibitor, staurosporine (1 microM). The collagen-induced release of [3H]arachidonic acid and formation of [14C]stearoyl-labelled lysophospholipids was inhibited by prior incubation with staurosporine, as was the formation of 3H-labelled thromboxane B2, thereby suggesting inhibition of the collagen-induced phospholipase A2 activity. The degradation of phosphatidylinositol (PI) and elevation of phosphatidic acid (PA) in platelets prelabelled with either radiotracer were also completely blocked by staurosporine pretreatment, indicating a suppression of collagen-stimulated phospholipase C activity. Suppressed phospholipase C activity may have been due to diminished thromboxane A2 formation since treatment with the dual cyclo-oxygenase/lipoxygenase inhibitor, BW755C, also resulted in an inhibition of the collagen-stimulated loss of 14C-labelled PI and rise in PA by 75-80%. Our results suggest that protein kinase, possible PKC, may be involved in the regulation of these phospholipases in collagen-stimulated human platelets.