Platelet aggregation in response to collagen, PMA, or ADP. Platelet aggregation was stimulated by collagen (15 μg/mL), PMA (100 nM), or ADP (10 μM) and optically monitored. (A-B) Representative aggregation curves in response to collagen in the presence (A) and absence (B) of 200 μg/mL fibrinogen. Arrows indicate the point of collagen addition. (C) Time from addition of agonist to 40% aggregation in response to ADP, PMA, and collagen. (D) For collagen-induced platelet aggregation, times from agonist addition to the point where light transmission was minimal (as indicated in panel A). For both panels C and D, bars show means ± SD of 3 independent experiments. ^*Significant difference between WT and Akt-1-null platelets (P < .05).