GLYCOPROTEIN IIB-IIIA ON PLATELET-DERIVED MICROPARTICLES, AND MICROPARTICLE STRUCTURES STUDIED BY ELECTRON-MICROSCOPY, CONFOCAL LASER MICROSCOPY AND CROSSED RADIO-IMMUNOELECTROPHORESIS

Shedding of microparticles from the platelet surface is usually associ ated with exposure of platelet procoagulant activity, Platelet-derived microparticles have been detected in blood in various disease states, Ira vitro, platelet stimulation with a number of different agonists r esults in formation of microparticles. In the present study, micropart icles induced by platelet stimulation by calcium ionophore or by membr ane incorporation of the terminal complement complex C5b-9 were studie d using electron microscopy, confocal laser microscopy, flow cytometry and radio-immunoelectrophoresis. When studied by electron microscopy, microparticle morphology was found to be dependent upon the induction method, Platelet stimulation with the calcium ionophore resulted in s maller, more homogeneous and electron dense microparticles than those induced by insertion of the terminal complement complex, With flow cyt ometry and confocal laser immunofluorescence microscopy, microparticle GPIIb-IIIa was demonstrated using a FITC-conjugated antibody to GPIII a. Surface-bound GPIIb-IIIa was demonstrated on the microparticles by immunoelectron microscopy, Crossed immunoelectrophoresis of detergent- solubilized microparticles visualized a very prominent GPIIb-IIIa immu noprecipitate are, and binding of [I-125]fibrinogen to microparticle G PIIb-IIIa was demonstrated by radio-immunoelectrophoresis. This sugges ts that the activated GPIIb-IIIa complex is preserved intact during th e shedding of microparticles from the platelet surface.