Effect of GPVI activation on tyrosine phosphorylation of HS1. Washed and aspirin-treated platelets were stimulated with convulxin (Cvx) or collagen for 30 seconds at 37°C as indicated. HS1 was immunoprecipitated (IP) as described, and the samples were analyzed for tyrosine phosphorylation (pTyr) by Western blotting (IB) using the monoclonal phosphotyrosine (4G10) antibody. Equal lane loading was assured by probing the samples with the HS1 antibody. The Western blot shown is representative of experiments performed using platelets from 3 different donors.