Fibrinogen binding kinetics in ADP- versus TRAP-stimulated platelets as compared with the abciximab binding rate.

(A) The time course of fibrinogen binding induced by 30 μM ADP (○) and 100 μM TRAP (●) was measured in washed platelets stimulated with the agonists for 15 minutes at 37°C in the absence of fibrinogen, followed by addition of labeled fibrinogen. (B) The time course of fibrinogen binding induced by 30 μM ADP (○) and 100 μM TRAP (●) was measured in washed platelets in the presence of labeled fibrinogen. (C) The abciximab (3 μg/mL) (▴) binding rate was measured in washed platelets. To superimpose abciximab and fibrinogen binding kinetics in platelets stimulated by 30 μM ADP (○) and 100 μM TRAP (●), the results are presented as a percentage of maximal binding (100% fibrinogen binding = binding at 10 minutes of stimulation with TRAP; 100% abciximab binding = binding at 10 minutes of incubation time). Data are means ± SEM from 4 to 6 independent experiments. Externalization and binding half-times (t_1/2) were deduced from each individual experiment. *P < .05 versus the ADP-stimulated fibrinogen binding rate (P < .05, ANOVA-Bonferroni).