Fig. 4. Modulation of exocytosis. Control (empty-vector-transfected) RBL cells (1-4), RBL-Syt II^- cells (5-8) and RBL-Syt III^- cells (9-12) were incubated for 30 minutes at 37°C in the presence of buffer (1,5,9), the Ca²⁺ ionophore (A23187, 10 µM, 2,6,10) and the combination Ca²⁺ ionophore (A23187, 10 µM) and TPA (50 nM) without (3,7,11) or with (4,8,12) prior treatment with TPA (50 nM) for 6 hours. The extent of release is presented as a percentage of total cellular ß-hexosaminidase activity. Data represent the average±s.e. of three separate experiments.