The magnitude and duration of P/S and P+2S changes at the sites of fusion differ in control and dynasore-treated cells. (A) A cumulative frequency histogram was generated to compare the frequency and magnitude of P/S changes observed with fusion in control (50 granules) and dynasore (27 granules)-treated cells. A greater fraction of fusion events show an associated increase in P/S with dynasore. The percent increase was calculated by taking the difference between the P/S at a particular frame (P/S)_f and the mean P/S of 10 prefusion frames (Ave_pre) divided by the mean; [(P/S)_f − Ave_pre]/Ave_pre. The two histograms are significantly different (P < 0.05 by Mann-Whitney test). (B) The decay of the initial increase in P/S after granule fusion was followed. Only those events that showed an increase of at least 6% in P/S (compared with the prefusion baseline) in the first 0.45 s after fusion and that could be followed for 31.5 s after fusion were considered (control, n = 29; dynasore, n = 25). The fraction of events with a P/S increase that subsequently declines to the baseline within 4.5, 9, 13.5, 18, 22.5, 27, and 31.5 s are plotted for the two conditions. (C) The P+2S of fusion events with a significant increase in P/S were aligned to their prefusion frames and averaged (control, n = 29; dynasore, n = 25). The data were also normalized to the mean of 10 prefusion frames. The arrow indicates a transient dip in P+2S in control cells. In dynasore-treated cells, an increase in P+2S is usually observed. The two datasets are significantly different at every point after time 0 (P < 0.05 by Student’s unpaired t test). Numbers are presented ± SEM.