Figure 5.

Selective activation of exocytosis by effector mutants of Rac1. Rac1 mutants were preactivated with GTPγS as described and applied to permeabilized mast cells as outlined in the legend to Figure 3. After a period of 7 min, the cells were stimulated by addition of Ca²⁺ (pCa5), and the incubation was continued for a further 20 min. The mutant Y40C was applied at a concentration of 3.9 μg ml⁻¹ activated protein, equivalent to 0.18 μM GTPγS, and the mutant F37A, which failed to induce secretion, was applied at 5.5 μg ml⁻¹ activated protein, equivalent to 0.26 μM. Results are presented as means ± SEM (n = 4 determinations). Similar results were obtained on five separate occasions.