Platelet cytoplasmic calcium concentration in PI3Kγ-null platelets. Washed murine platelets were incubated with a calcium fluorophore (Fura-2 AM) and then stimulated with either 1 U/mL thrombin or 10 mM ADP. The concentration of cytoplasmic calcium (nM) was quantitated as a function of time. (A) Representative fluorimetry tracings of experiments using thrombin- or ADP-stimulated wild-type and PI3Kγ-null platelets. (B) A graph displaying the mean ± SEM of the cytosolic calcium concentration for 3 experiments. (C) A graph demonstrating the influence of the extracellular calcium concentration on the ability of platelets to raise their cytoplasmic calcium concentration in response to 1 U/mL thrombin. The change in cytosolic calcium was normalized to the response seen in wild-type cells. The graph shows the mean ± SEM for 3 experiments.