Figure 3. Calcium-dependent steady-state priming depends on Syt-7 expression.

Titration of burst of secretion (i.e. secretion within the first 0.5 s of the uncaging flash, approximately corresponding to the fusion of the RRP and SRP) against pre-stimulation [Ca²⁺]. Top panel: post-stimulation [Ca²⁺], bottom panel: Burst size against pre-stimulation [Ca²⁺]. Syt-7 KO cells (vermilion) displayed no strong dependence on [Ca²⁺]. Calcium-dependent priming was strong in cells overexpressing Syt-7 (black), and intermediate in WT cells expressing Syt-7 at endogenous levels (persian green). Data information: Data are presented as mean ± SEM. *: p<0.05; ***p<0.001. Testing was by Kruskal-Wallis test with Dunn’s post-hoc test. Cells were pooled in 0.2 µM [Ca²⁺] bins from 0.0 µM to 0.8 µM and a final bin 0.8–1.2 µM for a total of 5 bins. Statistical testing is relative to the burst size at the lowest [Ca²⁺] bin for the same genotype. The number of cells in each bin from low to high [Ca²⁺]: WT: N = 29, 9, 9, 10, 22 cells; Syt-7 KO: N = 10, 12, 16, 43, 15 cells; Syt-7 KO + Syt-7: N = 12, 10, 28, 28, 20 cells.