Figure 5. Ultrafast depletion of the RRP of SVs.

(A) Average ΔC_m measured from rods filled with 10 mM EGTA and stimulated with a V_step to −18 mV for durations from 0.5 to 30 ms. Single exponential fits to points from 0.5 to 9 ms (red curve), and from 0.5 to 30 ms (dotted curve). Stimulations were delivered in ascending order, and only a single cycle per cell. (B) Comparison of ΔC_m derived from experiments with 0.5 or 10 mM EGTA in the pipette; voltage step durations: 0.5–30 ms. (C) Highlights the more rapid ΔC_m at the singular time point of 0.5 ms when rods were loaded with 0.5 mM EGTA (*, p: 0.0016; 6 and 8 cells for 0.5 and 10 mM EGTA, respectively). (D) Summary of lock-in amplifier traces recorded during 0.5 ms step depolarizations with either 0.5 or 10 mM EGTA in the pipette (6 and 8 cells, respectively). Dashed C_m traces represent an overlay of individual recordings (cells; each a different color), and the C_m trace presented in bold font represents the average response. Only an overlay of the average responses in low and high EGTA are presented for G_m and G_s with the blue traces corresponding to 0.5 mM EGTA and black traces corresponding to 10 mM EGTA. RRP, readily releasable pool; SV, synaptic vesicle.