Figure 5. Increasing extracellular Ca²⁺ increases spontaneous fusion rate.

(A) Cumulative probability histogram of spontaneous event rate per synapse per minute in 2 mM and 8 mM extracellular Ca²⁺ (n = 175 synapses from four coverslips for both conditions, KS_test p = 0.55 with Dmax = 0.8 fusion events per minute per synapse, with averages of 0.56 ± 0.02 and 0.49 ± 0.02 (Student's t-test p value = 0.2) events per minute per synapse for 2 and 8 mM Ca²⁺, respectively). (B) Cumulative probability histogram of spontaneous event rate per synapse per minute in 2 mM and 8 mM extracellular Ca²⁺ adjusted to count large amplitude events as two vesicle fusion events (n = 175 synapses from four coverslips for both conditions, KS_test p < 0.05 with Dmax = 0.6 fusion events per minute per synapse, with averages of 0.70 ± 0.02 and 0.76 ± 0.03 (t-test p value = 0.1) events per minute per synapse for 2 and 8 mM Ca²⁺, respectively. (C) Cumulative probability histogram of spontaneous event rate per synapse per minute in Tris-buffered (50 mM) 2 mM and 8 mM extracellular Ca²⁺ solutions (n = 150 synapses from three coverslips for both conditions, KS_test p < 0.05 with Dmax = 0.5 fusion events per minute per synapse, with average 0.4 ± 0.02 and 0.5 ± 0.02 (t-test p value <0.05) fusion events per minute per synapse for 2 and 8 mM Ca²⁺, respectively. (D) Cumulative probability histogram of spontaneous event rate per synapse per minute in 2 and 8 mM extracellular Ca²⁺ solution containing folimycin (n = 175 synapses from four coverslips for 2 mM Ca²⁺ and 216 synapses from four coverslips for 8 mM Ca²⁺; KS_test p < 0.05 Dmax = 0.8 fusion events per synapse per minute, with average rates of 0.4 ± 0.02 and 1.1 ± 0.02 (p value <0.05) fusion events per minute per synapse for 2 and 8 mM Ca²⁺, respectively).

DOI: http://dx.doi.org/10.7554/eLife.03658.009