Protein kinase C inhibitors suppress disc-sphere changes of human platelets, as assessed with the shape-change parameter.

Changes in the shape of human platelets and the biochemical mechanism responsible were evaluated, using the shape-change parameter. Neither the Na+/H+ exchanger, nor intracellular or extracellular calcium ions (Ca2+) affected disc-sphere changes induced by low doses of thrombin. Treatment with inhibitors of Ca2+ mobilization, calmodulin or mysoin light-chain kinase had no significant effect on the shape change of platelets. Staurosporine and H-7, both of which are inhibitors of protein kinase C, inhibited disc-sphere changes at low concentrations. Moreover, calphostin C, a specific inhibitor of protein kinase C, effectively inhibited thrombin-induced shape change, as assessed by the shape-change parameter, in a dose-dependent manner. 1-Oleoyl-2-acetyl-glycerol and 1,2-dioctanoyl-glycerol, which are synthetic protein kinase C activators, induced shape changes similar to those induced by thrombin. A decrease in the surface area of platelet images on scanning electron micrographs was used to quantify the disc-sphere transformation. The mean platelet areas was significantly decreased after stimulation with thrombin or 1-oleoyl-2-acetyl-glycerol. Pretreatment with H-7 inhibited the thrombin-induced disc-sphere change, as assessed by changes in the platelet surface area. Our results obtained with various inhibitors suggest that thrombin-induced platelet change, as assessed by the shape-change parameter, are associated with activation of protein kinase C.