STRUCTURAL CHARACTERIZATION OF PLATELETS AND PLATELET-DERIVED MICROVESICLES
A.A. Ponomareva,1,2 T.A. Nevzorova,2 E.R. Mordakhanova,2 I.A. Andrianova,2
R.I. Litvinov 2
1 Kazan Institute of Biochemistry and Biophysics RAS, Kazan, 420111, and
2 Kazan (Volga Region) Federal University, Kazan, 420012;
1 e-mail: na.ponomareva@mail.ru
Platelets are the anucleated blood cells, wich together with the fibrin stop bleeding (hemostasis). Cellular microvesicles are membrane-surrounded microparticles released into
extracellular space upon activation and/or apoptosis of various cells. Platelet-derived macrovesicles from the major population of circulating blood micro-particles that play an important
role in hemostasis and thrombosis. Despite numerous studies on the pathophysiology of platelet-derived macrovesicles, mechanisms of their formation and structural details remain
poorly understood. Here we investigated the ultrastructure of parental platelets and platelet-derived microvesicles formed in vitro by quiescent cells as well as by cells stimulated
with one of the following activators: arachidonic acid, ADP, thrombin, calcium ionophore A23187. Using transmission electron microscopy of human platelets and isolated microvesicles,
we analyzed the intracellular origin, steps of formation, structural diversity, and size distributions of the subcellular particles. We have revealed that thrombin, unlike other stimuli, not
only induced vesiculation of the plasma membrane but also caused break-up of the cells followed by formation of microparticles that are comparable with microvesicles by size.
A fraction of these microparticles contained cellular organelles surrounded by a thin membrane. The size of platelet-derived macrovesicles varied from 30 nm to 500 nm, however, the
size distributions depended on the nature of a cell-activating stimulus. The results obtained provide new information about the formation of platelet-derived macrovesicles and their
structural diversity, wich is important to understand their multiple functions in normal and disease states.
Key words:
platelets, cellular macrovesicles, blood microparticles, platelet activation, cell ultrastructure, electron microscopy
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