Budkova V., Balandina A., Zapariy A., Ataullakhanov F., Panteleev M.

XXIVth Congress of the International Society on Thrombosis and Hemostasis (ISTH). 2013. Amsterdam, Netherlands.

Background
Activated platelets affect blood coagulation by secreting contents of their granules and exposing phosphatidylserine on the outer leaflet of the cell membrane.

Aims
We investigated the influence of platelets on the process of spatial fibrin clot growth in the reaction-diffusion in vitro experimental model (Thrombodynamics assay).

Methods
Spatial clot growth was monitored by light scattering in recalcified platelet-rich plasma (PRP) or in platelet-free plasma (PFP) of healthy subjects following activation with immobilized tissue factor (TF) at either high or low density (80 or 8 pmole/m2, respectively).

Results
When coagulation was initiated by high TF density, platelets only moderately increased spatial clot growth velocity (V) from 25.7±1.9 to 38.7±8.3 µm/min (n=3, p=0.08); a similar effect was achieved with artificial phosphatidylserine microvesicles (V=38.1±1.4 µm/min).

On the contrary, in experiments with low TF density activation, platelets greatly increased V (from 6.5±2.3 µm/min in PFP to 42.6±10.6 µm/min in PRP; n=4, p<0.05). In heparin-supplemented plasma (0.09МЕ/ml) activated with high TF density V was 12.2±2.3 µm/min in PFP and 27.3±6.2 µm/min in PRP (n=9, p<0.05). Addition of prostaglandin E1 (platelet activation inhibitor) in heparinized PRP decreased V in 1.5 ±0.4 times (n=3, p=0.1). Apyrase and wortmannin did not show any effect on the spatial clot growth.

Conclusion
Clot growth rate in a reaction-diffusion system is insignificantly affected by platelets in normal conditions (physiological TF density and inhibitors concentration). Nevertheless the physiological concentration of the platelets in the plasma decrease the influence of clotting factors such as TF density decrease or heparin presence making system less sensitive to clotting conditions.

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