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A Well-Defined Readily Releasable Pool with Fixed Capacity for Storing Vesicles at Calyx of Held
Fig 3
Frequency jump experiments.
A. Average traces from n = 16 preparations (3 trials per preparation) where the stimulation frequency was abruptly increased to 300Hz after either 500ms (blue) or 750ms (magenta) of 100Hz stimulation. Black trace is 200ms of 300Hz stimulation from the same preparations. Stimulus artifacts were blanked. Ca2+ was 2mM throughout; KYN was 1mM. 4 preparations included in the full analysis in the Results were excluded from these display traces because stimulation during 300Hz stimulation was 150ms instead of 200ms. B. Overlaid integrals from 3.33ms segments. The double lines during 100Hz stimulation are because 
of segments contained only asynchronous responses whereas every 3rd contained a synchronous response, which was larger. C. Overlaid integrals of 10ms segments revealing a robust increase in the release rate caused by increasing stimulation to 300Hz.D. Indices of increase in response caused by frequency jumps (see Results). Solid bars are for trials where stimulation frequency was increased to 300Hz, open bars are matched baseline values where stimulation was instead maintained at 100Hz. E. Average of traces from n = 3 preparations from frequency jump experiments where extracellular Ca2+ was 4mM. KYN was 2mM, explaining why the initial response sizes were not larger than in Panel (A). F. Integrals of segments for experiments in 4mM Ca2+analogous to Panel (C).G. Response increase after frequency jumps initiated after 500 or 750ms of 100Hz stimulation in 2mM Ca2+ (n = 7; segments were 3.33ms). The baseline response size during matched 100Hz stimulation was calculated by averaging three consecutive 3.33ms segments to smooth out the variation between sequential segments seen in Panel (B), and was subtracted beforehand. Colored lines are estimates of vesicle recruitment to sites newly vacated by the frequency jump: blue assumes Eq 1 with 
; green is the overestimate where bulk refilling is maximal from the start; brown is the underestimate where recruitment does not begin until all release sites have been vacated (see Results).
doi: https://doi.org/10.1371/journal.pcbi.1004855.g003