Analysis of protein Tyr phosphorylation in resting and thrombin-challenged platelets isolated from blood of healthy donors or Ph-MPD patients. Platelets were obtained from healthy donors, and PV or ET patients as detailed in “Platelet isolation and treatment.” Cells were stimulated with 100 mU/mL thrombin (Thr) for the indicated times in the presence of vehicle (lanes 1-3), or 10μM AG490 (lanes 4-6), or 10μM PP2 (lanes 7-9). Platelets were then lysed and analyzed by Western blot with anti–P-Tyr and β-actin (loading control) antibodies as described in “Western blot analysis of cellular lysates.” The figure is representative of experiments performed with 20 normal, 11 PV, and 30 ET samples.