Figure 5.

Large spontaneous events involve a different vesicle pool than evoked release. (A) Shown are examples of spontaneous events that occurred before and after a smaller event evoked by a depolarizing step to −10 mV (2 ms). (B) Ratio of the amplitude of spontaneous multiquantal events relative to an evoked response in the same trial is shown. These ratios are plotted as a function of the timing of the spontaneous event before (open circles) or after (filled circles) the test stimulus (2 ms, −10 mV) applied at time 0. Spontaneous and multiquantal events were included in this analysis only if both exceeded 30 pA. Data were from 1-s (n = 5) and 2-s (n = 18) trials. (C) Shown is an example of a large spontaneous multiquantal event that occurred 650 ms after a depolarizing pulse (2 ms to 10 mV) failed to evoke release.