Figure 4.

Effects of pertussis toxin on hormone-regulated cAMP or inositol trisphosphate accumulation in 293 cells. Cells transfected with empty vector were incubated with the appropriate radioactive precursor for 24 or 48 hr and treated with 100 ng/ml pertussis toxin (PTx) for 4 hr and then with the indicated hormone(s) before the cells were lysed. (A) Cells were treated with 5 μM isoproterenol (Iso) ± 1 μM somatostatin (Stt) for 15 min. Pertussis toxin prevented the somatostatin-induced inhibition of cAMP accumulation. The bars represent the mean ± SD of five determinations made in two independent experiments. (B) Pertussis toxin had no effect on the ability of bradykinin (BK, 100 nM) to stimulate inositol trisphosphate synthesis in cells treated with the hormone for 30 sec. The bars represent the mean ± SD of seven determinations made in two independent experiments.