ИСТИНА

Background: Binding of coagulation factors to phosphatidylserine (PS)-exposing procoagulant activated platelets and formation of membrane-dependent complexes on their surface are critical for blood coagulation. Procoagulant platelets have a special morphology including a small (approximately 1 lm radius) “cap”-like convex region containing a lot of adhesive proteins, and a large “balloon” structure. Aims: The aims of this study was characterised of spatial distribution of coagulant factors on the membrane of activated platelets. Methods: The spatial distribution of coagulation factors to activated platelets was studied with an Axio Observer Z1 confocal microscope (Carl Zeiss, Jena, Germany) using fluorescein-labeled coagulation factors or specific antibodys. For study structure of the “caps” was used transmission electron microscope JEM-1400 (JEOL Tokyo, Japan). Results: Here we show that blood coagulation factors bound to procoagulant platelets including factors IXa (FIXa), Xa/X (FXa/FX), Va (FVa), VIII (FVIII), prothrombin, and phosphatidylserine-sensitive marker annexin V are co-localized and highly concentrated in the “caps” of procoagulant platelets. A three-dimensional computer simulation model of intrinsic tenase based on these data revealed how localization of proteins in the cap can promote procoagulant reactions by two orders of magnitude due to increased local concentrations. Transmission electron microscopy indicated a complex structure of the “caps” with numerous membrane folds possibly suggesting additional roles of this phenomenon. In platelet thrombi formed in whole blood on collagen under arterial shear conditions, ubiquitous “caps” with increased annexin V binding were observed indicating relevance of this mechanism under physiological conditions. Conclusions: In this work was shown an essential heterogeneity in the surface distribution of major coagulation factors on the surface of procoagulant platelets and suggest its importance in promoting membrane-dependent coagulation reactions.