Effect of tyrosine kinase inhibitors on p21rac activation. (A) Neutrophils were pretreated for 20 minutes with 100 μmol/L genistein, 100 μmol/L erbstatin, 50 μmol/L PD098059, 10 μmol/L SB203580, 50 μmol/L PP1, or 10 μmol/L LY294002 after stimulation with fMLP (1 μmol/L) for 10 seconds. (B) Neutrophils were either untreated (a), pretreated with 10 μmol/L LY294002 for 20 minutes and then GM-CSF (10⁻¹⁰ mol/L) for 20 minutes (b), or with GM-CSF (10⁻¹⁰ mol/L) for 20 minutes (c). At the time indicated by the arrowhead, samples were stimulated with fMLP (1 μmol/L). Oxygen consumption was measured using a Clark oxygen electrode as previously described.