Fig. 2

Spontaneous fusion energy barrier measurement at changing lithium concentration. (A) Two populations of SUVs were prepared. First, a fluorescent population containing NBD-PE and Rhodamine-PE labelled lipids. The other SUV population does not contain any fluorescent lipid. NBD-PE fluorescence is quenched by the presence of Rhodamine-PE in the vicinity. When a fluorescent vesicle and a non-fluorescent vesicle spontaneously fuse, the fluorescent lipids are diluted inducing a reduction of the quenching effect and therefore an increase in NBD-PE fluorescence. Recording NBD-PE fluorescence over time gives access to the fusion kinetics. (B) Vesicle fusion kinetics over time for vesicle in 150 mM potassium and no lithium at different temperatures. As temperature increases, the initial slope for fusion increases. Fusion advancement at each time point is measured by the average over a triplicate (n = 3) and error bars are SEM. (C) Arrhenius plot from spontaneous fusion kinetics depending on temperature. The slope of the fit in natural log-scale corresponds to the apparent fusion energy barrier of fusion. Each point in the plot is the average of three fusion slopes (n = 3) at a defined temperature and error bars are SEM. (D) Table with activation energy barrier for spontaneous fusion depending on lithium concentration. As lithium concentration increases, fusion activation energy barrier increases. Each point is the average of three slopes of Arrhenius plots (N = 3) and error bars are SEM. In the right column is the fusion energy barrier increase associated for each concentration measured taking as reference the activation energy barrier in absence of lithium.