Figure 8.

a) Concentration–effect relationship for the enhancement of secretion by preactivated Cdc42/G25K from mast cells stimulated by Ca²⁺ alone, or by Ca²⁺ plus GTPγS. In this experiment, the cells were run down for 7 (Ca²⁺ only) or 17 (Ca²⁺ plus GTPγS) minutes before application of the stimulus. Results are expressed as means ± SEM (n = 4). Similar results were obtained on four separate occasions. □, Cells stimulated with Ca²⁺ (pCa5) alone; •, cells stimulated by Ca²⁺ plus GTPγS (100 μM); ▴, unstimulated cells. (b) Data of Figure 7a presented as Hill plots. For secretion stimulated by Ca²⁺ alone, slope p = 0.9 (r = 0.98, n = 5 data points); for secretion stimulated by Ca²⁺ plus GTPγS, p = 0.6 (r = 0.97, n = 8 data points).