Figure 6.

SytI-CpxII antagonism determines fusion pore dynamics. (A) Properties of the main amperometric spikes and their prespike signals, displayed as cumulative frequency distribution for the indicated parameters. Data were collected from the following genotypes (number of events): wt (black; 8,350), CpxII ko (red; 6,051), SytI ko (green; 2,051), CpxII-SytI dko (purple; 2,431), and wt + CpxII (blue; 1,815). (B) Exemplary single-release events with similar charge and 50–90% rise time for wt, CpxII ko, SytI ko, CpxII-SytI dko, and wt + CpxII. (C and D) SytI absence increases fusion pore expansion time and prespike charge, both of which are restored by additional loss of CpxII. CpxII expression in wt cells mimics the SytI ko phenotype. Values are given as means of the median determined from the parameter’s frequency distribution for each cell. Numbers of cells are depicted in the bars (>40 events/cell). (E) Dependence of the prespike duration (left) and charge (right) on the indicated [Ca]i (micromolars) for wt and CpxII ko. Numbers of cells are depicted in bars. *, P < 0.05; ***, P < 0.001, Student’s t test for comparison between groups at the same [Ca]i in E. Error bars indicate means ± SEM.