Comparison between the loss of platelet membrane asymmetry, microvesiculation and the tyrosine phosphorylation of proteins

Abstract

Platelet activation by agents such as the Ca 2+-ionophore A23187 or Ca 2+-ATPase inhibitors leads to the generation of a procoagulant surface and the formation of microparticles. These responses are late events of platelet activation and readily detected by flow cytometry using annexin V-FITC as an aminophospholipid probe. One Ca 2+-ATPase inhibitor, 2,5-di-(tertbutyl)-1,4-benzohydroquinone induced aminophospholipid exposure without microparticle formation. Previous work has shown that microparticle formation is strictly linked to the activation of calpain, a thiol-protease that modifies the platelet cytoskeleton and some signal transduction enzymes. We now report how the detection of platelet tyrosine phosphorylation by western-blotting clearly shows that when platelet activation and aminophospholipid exposure are accompanied by microparticle formation there is a decrease in the tyrosine phosphorylation of proteins.