Effects of pertussis toxin (PTX) on calcium mobilization in three different cells. The cells were treated for 16 hours with PTX at the concentrations indicated next to each tracing (in nanograms per milliliter). Agonist-induced calcium mobilization was then measured using indo-1 AM as a fluorescent calcium indicator. Relative intracellular calcium levels are shown. The arrows mark the time points when agonist was applied. Each horizontal bar represents approximately 50 seconds.