FIGURE 4.

Ach- and ionomycin-induced exocytic responses in VAMP8 knock-out pancreas show a selective reduction in secondary fusion compared with WT. A, shown are plots of cumulative numbers of fusion events per length of lumen for stimulation with ACh (upper graph) and ionomycin (lower graph). WT primary events (black lines; S.E., black dotted lines) show little difference compared with primary events in VAMP8 knock-out mice (gray lines; S.E., gray dotted lines). In contrast, comparison of the secondary fusion events shows a dramatic and significant reduction in VAMP8 knock-out (gray lines; S.E., gray dotted lines) compared with WT (black lines; S.E., black dotted lines). B, shown is a histogram of the relative reduction infusion events for ACh stimulation (left graph). This shows no significant overall reduction in total fusion events in the VAMP8 knock-out mice but a significant drop in the proportion of secondary fusion events (gray block within the histogram). The ratios of secondary to total fusion events for all conditions (right graph) show this loss of secondary fusion is consistent with all three of the stimuli we used.