Platelet aggregation induced by high concentrations of collagen does not depend on the ERK2 pathway.

(A) Light transmission (%) recordings in apyrase-treated washed platelets stimulated with 2 μg/mL collagen alone (control), in the presence of 0.5 μM α,β-meATP, or after preincubation with 1 μM U-0126, as indicated. Time bar is included. (B) Parallel Western blot analyses of ERK2 phosphorylation in these platelet samples. ERK2 phosphorylation was induced by 1 or 2 μg/mL collagen for 4 minutes alone or after preincubation with 1 μM U-0126 or 5 mM EGTA, as indicated; ERK2 phosphorylation was also analyzed after platelet stimulation for 4 minutes with 2 μg/mL collagen alone or in the presence of 0.5 μM α,β-meATP.