Fusion pore stability is affected by C- but not N-terminal destabilization of the SNARE complex. (Ai and Bi) Examples of spikes recorded by means of carbon fiber amperometry. (Aii and Bii) Mean of cumulative probability (Cum. Prob.) distributions of the prespike foot duration shows a shift to shorter feet for C-terminal synaptobrevin mutants (L84A in Aii and L84N in Bii). (Aiii and Biii) The mean foot duration (mean of cell medians) of C-terminal mutants is significantly reduced. Mean ± SEM is shown (A: WT rescue, n = 16 cells; VAVA, n = 19 cells; and L84A, n = 19 cells; and B: control, n = 14 cells; LATA, n = 15 cells; and L84N, n = 19 cells; and *, P < 0.05 in one-way ANOVA after log transformation yielded normally distributed homoscedastic data). (C) Proposed energy landscape for fusion (line), including barriers for vesicle priming, fusion triggering, and fusion pore expansion. The kinetic scheme comprises rate constants for pore formation (k_o), pore closure (k_c), and pore dilation (k_f). In this model, the lifetime of the pore (τ_o) is defined by the inverse sum of the rate constants k_c and k_f. The dashed line shows the proposed energy landscape after C-terminal mutation in syb-2.