FIGURE 6:

(A) Averaged, normalized intensities of Syt-1 (n = 36; seven cells) and Syt-7 (n = 51; six cells) fusion events ± SEM. Means are significantly different after 2.8 s (*p < 0.05, Student's t test). (B) Chromaffin cells expressing Syt-1 or Syt-7 pHluorin were exposed to low-pH (5.5) PSS for ∼8-s intervals after an initial 30-s stimulation with 56 mM KCl in the presence of bafilomycin. Low-pH-insensitive events were assumed to have undergone endocytosis and are expressed as percentage of total fusion events. The probability of a fusion event undergoing endocytosis (cavicapture) with Syt-7 (six cells) was significantly different from that with Syt-1 (seven cells; **p < 0.01, binomial probability). P/S (C) and P + 2S (D) lifetimes for individual Syt-1 and Syt-7 fusion events. Syt-1 events are short lived. Only nine of 36 P/S increases and one of 23 P + 2S changes (increases and decreases) persist for >5 s for Syt-1. In contrast, most Syt-7 fusion events are associated with P/S (48 of 51 events) and P + 2S (22 of 37 events) changes lasting >5 s.