Figure 2. Resolution and analysis of evoked ΔC_m.

(A) The I_m presented at the top of the figure is dominated by the sine-wave voltage protocol used to derive the lock-in amplifier outputs: C_m, G_m, and G_s. The protocol consisted of a series of 100 ms sine-wave segments presented in gray, which bracket the stimulation segment depicted in black (arrow points to the 9 ms depolarizing voltage step). (B) Responses to a series of step depolarizations for the indicated durations are presented. The approach used to bin the data in (A) and create the plot in (B) are illustrated schematically. The G_m and G_s data points that are filled in black mark the stimulation segments. The dashed, downward pointing arrow following the 3 ms stimulation highlights an unusually large endocytotic, downward step in C_m (see text). (C, D) Plot the individual C_m traces for each evoked response. Traces in (D) were low-pass filtered to a corner frequency (f_c) of 20 Hz, and in (C) a f_c of 200 Hz was used. (E) Illustrates how ΔC_m was quantified over both baseline (between stimulation) and stimulation segments (see Materials and methods). (F) Chronological plot of ΔC_m during baseline and stimulation segments. (G) Summary plot with two y-axes: ‘ΔC_m’ and ‘equivalent number of SVs,’ versus step duration (x-axis). The conversion factor for calculating the number of SVs is described in Materials and methods. The I_Ca traces measured from this cell are presented in Figure 1C. SV, synaptic vesicle.