Effect of Ca²⁺ depletion on p21rac activation. (A) Neutrophils were stimulated with fMLP (10⁻⁸ mol/L) for the time indicated. p21rac activation was determined as previously described. In cells from the same donor change in [Ca²⁺]_i was measured after stimulation. The arrowhead indicates addition of fMLP (10⁻⁸ mol/L). (B) Neutrophils were Ca²⁺-depleted before stimulation with fMLP (10⁻⁸ mol/L). p21rac activation and [Ca²⁺]_i were measured as described above.