Platelet FXIII-A function requires platelet activation. (A) (△) FXIII-depleted thrombi were prepared with (▪) 5 × 108 plts/mL, (●) 5 × 108 plts/mL preincubated with 100 nM prostaglandin E1 (PGE1) and 1 mM theophylline, or (□) 5 × 108 plts/mL preincubated with 100 nM PGE1 and 1 mM theophylline plus a TG inhibitor (1 mM). **P < .01; ***P < .001 vs FXIII-depleted thrombi + 5 × 108 plts/mL (n = 6). (B) (△) FXIII-depleted thrombi; (●) 5 × 108 plts/mL preactivated for 5 minutes or 1 hour at 37°C with 200 μg/mL collagen and 200 μM TRAP-6; (□) 5 × 108 plts/mL preactivated for 5 minutes or 1 hour at 37°C with 200 μg/mL collagen and 200 μM TRAP-6 including a TG inhibitor (1 mM). *P < .05; ***P < .001 vs FXIII-depleted thrombi + 5 × 108 plts/mL. ††P < .01; †††P < .001 vs FXIII-depleted thrombi + 5 × 108 plts/mL preactivated for 5 minutes (n = 6). (C) Platelets (5 × 108 /mL) were preactivated with 200 μg/mL collagen and 200 μM TRAP-6 for up to 1 hour and FXIII activity (IU/mL) was measured. **P < .01; ***P < .001 vs 5 minutes preactivation. Data are expressed as mean with standard error of the mean n= 3.
