Comparison of the time course of platelet aggregation and ATP release induced by HIT sera no. 3 (A) and 4 (B) and 1 nmol/L thrombin (C). Agonists were added at time points indicated by arrows. Ten μg/mL PF4 and 0.5 U/mL heparin was added 1 minute before adding HIT sera as agonists. One, 2, and 5 minutes after adding the agonists aliquots were taken for ATP measurement. Arrows and numbers indicate released ATP (nmol/10¹⁰ platelets). The aggregation curves and ATP release data are representative of the results from three experiments.