Figure 7.

Comparing the effects of acoustic experience or external Ca²⁺ on Ca²⁺ influx and PPR. A, Model of Ca²⁺ influx (top) with Ca_peak = 50.9 nM, Ca_rest = 67.1 nM, and decay τ = 52.6 ms, and the modeled ΔF/F signal (bottom, green lines) for a dye with characteristics similar to calcium-green 1 (K_D = 540 nM, 15-fold change in brightness on binding Ca²⁺). The model was fit to a ΔF/F recorded from a control endbulb (bottom, black line). B, Fits of model illustrated in A (lines) to imaging data from Figure 5 for the three acoustic conditions (markers). C, Ca_peak and Ca_rest from different acoustic conditions are measured from the model (Ctrl: n = 14; Nr: n = 14; Occ: n = 11). D, Comparison between Ca²⁺ and PPR changes for endbulbs manipulated by acoustic conditions (red, closed markers) or Ca_e (black, open markers). For acoustic conditions, Ca²⁺ data are from the modeling analysis in B, and PPR data are from Figure 4. For Ca_e, data are from the imaging and electrophysiology experiments of cooperativity in Figure 6. Overlap of these curves suggests that changes in Ca²⁺ account for acoustically-driven changes in PPR.