Platelet procoagulant activity in response to thrombin and TRAP.
(A) Annexin V-FITC binding to gel-filtered platelets activated with 1 to 200 μmol/L TRAP (n = 4); ● indicates 25 000 platelets/μL. The fluorescence of 5000 platelets per measuring point was determined by flow cytometry. Insert: aggregation of gel-filtered platelets induced by 25 μmol/L TRAP. The platelet counts were adjusted to 1 × 108/mL. The data shown are representative of 3 similar experiments. (B) After pretreatment with 50 μmol/L TRAP, platelets were activated with 0.05 to 2 U/mL thrombin (n = 3); ● indicates 25 000 platelets/μL, ○, 25 000 platelets/μL after preactivation with TRAP. The fluorescence of 5000 platelets per measuring point was determined by flow cytometry. (C) Thrombin generation by the prothrombinase complex was measured on resting, thrombin-activated (0.5 U/mL) gel-filtered platelets, TRAP-activated (50 μmol/L) gel-filtered platelets, as well as thrombin-activated (0.5 U/mL) gel-filtered platelets after pretreatment with 50 μmol/L TRAP, in the presence of 0.4 U/mL factor Xa and 6 μmol/L CaCl2 (n = 3); ○ indicates 25 000 platelets/μL; ●, 25 000 platelets/μL activated with thrombin; ▵, 25 000 platelets/μL activated with 50 μmol/L TRAP; ▴, 25 000 platelets/μL pretreated with TRAP, activated with thrombin. Data are the mean of the indicated number (n) of experiments using platelets from different donors.
