Abstract
Background The functional links between the activation of platelets and the coagulation system have not been clarified. Methods and Results Immobilized collagen fibrils were perfused with human blood containing fluoresceinated platelets in the presence of various concentrations of thrombin inhibitor. Coagulant activity around platelet thrombi was detected using a FITC-conjugated antibody against the fibrin monomer complex (F-405). Intra-cytosolic calcium ion concentrations ([Ca2+]i) in individual platelets and the volume of thrombi were detected with an ultrafast confocal laser microscope equipped with a piezo-motor control unit. The volume of platelet thrombi formed after 8 min of blood perfusion in the presence of 10, 25, 50, and 100 μmol/L argatroban was 7.69±0.46 μm3, 6.61±1.96 μm3, 3.63±1.54 μm3, and 1.67±0.75 μm3, respectively. There was a positive correlation between the volume of platelet thrombi and the amount of fibrin monomer complex produced around them. The [Ca2+]i of the platelets forming the thrombi oscillated between a minimum of 92.0±57.4 nmol/L, 120.1±68.1 nmol/L, and a maximum of 217.6±131.5 nmol/L, 367.6±189.1 nmol/L, respectively, in the presence of 100 and 10 μmol/L argatroban. Conclusions The results suggest a crucial role of coagulant activity in both the generation of fibrin and the growth of platelet thrombi.
