[Thrombin-induced platelet aggregation in the presence of negatively charged liposomes]

The negatively charged liposomes of different phospholipid composition were examined for their effects on platelet aggregation induced in vitro by thrombin. Negatively charged dicetylphosphate and phosphatidylinositol failed to affect the aggregation of platelet suspension. The liposomes that contain yolk lecithin-phosphatidylserine-cholesterol (4:4:2) caused a dose-dependent increase in their aggregation. Replacement of yolk lecithin by dipalmitoylphosphatidylcholine eliminated the activating effect of phosphatidylserine. It is suggested that platelet activation is associated with the transfer of phosphatidylserine from liposomes to cells.