Figure 7.

FM1-43-labeled SVs with delayed availability for release preferentially replenish the reserve pool. A, Cultures were loaded with 10 μm FM1-43 using a train of 800 action potentials (80 Hz) at both S1 and S2. In both cases, dyes were washed away immediately after stimulation and cultures were left to rest for either 10 min (standard unload) or 2 min (immediate unload) before unloading. At both S1 and S2, the RRP was unloaded with a train of 60 action potentials (30 Hz), and the reserve pool (RP) was unloaded with three consecutive trains of 400 action potentials (40 Hz). Cells were left to rest for 20 min between S1 and S2. B, A representative trace of the average fluorescence drop of nerve terminals is shown (standard unload, S1; immediate unload, S2). Unloading stimulations are represented by bars. Traces were normalized (between 1 and 0) to the size of the S2 recycling pool (RRP + RP) for each nerve terminal. C, Average proportion of the RRP and RP in both S1 and S2 expressed as a percentage of the S2 SV recycling pool (RRP, solid bars; RP, dotted bars). In all experiments, n = 3; error bars represent ±SEM; *p < 0.05, **p < 0.01, ***p < 0.001, one-way ANOVA.