COMPARISON BETWEEN THE LOSS OF PLATELET MEMBRANE ASYMMETRY, MICROVESICULATION AND THE TYROSINE PHOSPHORYLATION OF PROTEINS

Platelet activation by agents such as the Ca2+-ionophore A23187 or Ca2 +-ATPase inhibitors leads to the generation of a procoagulant surface and the formation of microparticles. These responses are late events o f platelet activation and readily detected by flow cytometry using ann exin V-FITC as an aminophospholipid probe. One Ca2+-ATPase inhibitor, 2,5-di-tertbutyl)-1,4-benzohydroquinone induced aminophospholipid expo sure without microparticle formation, Previous work has shown that mic roparticle formation is strictly linked to the activation of calpain, a thiol-protease that modifies the platelet cytoskeleton and some sign al transduction enzymes. We now report how the detection of platelet t yrosine phosphorylation by western-blotting clearly shows that when pl atelet activation and aminophospholipid exposure are accompanied by mi croparticle formation there is a decrease in the tyrosine phosphorylat ion of proteins.