Platelet aggregation in response to thrombin. Platelet aggregation was stimulated with thrombin and optically monitored in a Lumi-Aggregometer. (A) Representative aggregation curves in response to thrombin at 0.04 U/mL (i), 0.1 U/mL (ii), and 0.4 U/mL (iii). Arrows indicate the points of agonist addition. (B) Time from the addition of 0.1 U/mL thrombin to 20%, 35%, 50%, and 55% aggregation in WT (•) and Akt-1-null platelets (○). Means ± SD of 3 independent experiments are shown. (C) WT and Akt-1-null platelets were stimulated with thrombin at 0.04, 0.06, 0.1, 0.4, and 1 U/mL. Bars represent means ± SD of time from addition of agonist to 50% aggregation from 3 independent experiments. (D) Platelets from WT and Akt-1 null mice aggregated by 0.1 U/mL thrombin were visualized using phase contrast microscopy (Leica) and photographed (Micromax). Scale bars equal 20 μm. Images were acquired using a Leica DMIRB phase contrast microscope, objective × 20, and a Micromax RTE/CCD-1300-V-HS camera.