Role of Src-family tyrosine kinases in the tyrosine phosphorylation of HS1. Aspirin-treated and washed human platelets were stimulated with 100 ng/mL convulxin in the presence or absence of PP1 (10 μM), PP2 (10 μM), or the control compound PP3 (10 μM) at 37°C, and the reaction was stopped by adding 2× cell lysis buffer. Dimethyl sulfoxide (DMSO) was used as a vehicle control. The stimulation time for convulxin was 30 seconds, and the incubation time for PP1, PP2, and PP3 was 10 minutes at 37°C. HS1 was immunoprecipitated (IP) as described, and the samples were analyzed for tyrosine phosphorylation by Western blotting (IB) using the monoclonal phosphotyrosine (4G10) antibody. The Western blots shown are representative of experiments performed using platelets from 3 different donors.