Figure 7. IHC exocytosis is normal for strong depolarizations but mildly reduced for weak ones.

(A) Representative Ca²⁺-currents (top) and corresponding low passed-filtered membrane capacitance (ΔC_m) traces recorded from RBE^WT/WT and RBE^KO/KO IHCs upon 50 ms depolarizations from −69 to −14 mV. (B) Cumulative exocytosis (exocytic ΔC_m, top) and corresponding Ca²⁺-charge (Q_Ca, bottom) of RBE^WT/WT (n = 11 cells, N = 8) and RBE^KO/KO (n = 12 cells, N = 7) IHCs as a function of stimulus duration (2 to 200 ms to −14 mV) were unaltered in RBE^KO/KO IHCs. Data is presented as mean ± S.E.M as for (F). (C) Relating ΔC_m to the corresponding Q_Ca indicated comparable Ca²⁺ efficiency of exocytosis between RBE^WT/WT and RBE^KO/KO IHCs. Mean ± S.E.M. for each pulse duration is presented in black and red; individual IHCs data points are overlaid. (D) Mean ΔC_m traces (shaded areas: S.E.M.) in response to trains of 20 ms depolarizations from −87 to −17 mV (20 stimuli separated by 160 ms) of RBE^WT/WT (n = 11 cells, N = 5) and RBE^KO/KO (n = 13 cells, N = 8) IHCs show comparable exocytic ΔC_m. (E) Representative low pass-filtered ΔC_m traces in response to a pair of 20 ms pulses to −17 mV, separated by a 50 ms of inter-pulse interval (IPI). (F) Ratios of exocytosis (ΔC_m2/ ΔC_m1) to a pair of 20 ms pulses with varying inter-pulse intervals (50, 110, 260 and 510 ms) reveal a comparable recovery from RRP depletion between RBE^WT/WT (n = 9 cells, N = 6) and RBE^KO/KO IHCs (n = 9 cells, N = 6). (G) Representative low pass-filtered ΔC_m traces in response to 100 ms step-depolarizations to −45, –43 and −41 mV. (H) Box plot and single values of ΔC_m elicited by 100 ms step-depolarizations of RBE^WT/WT (n_min = 10 cells, N = 8) and RBE^KO/KO (n_min = 9 cells, N = 9) IHCs to different potentials. Exocytic ΔC_m of RBE^KO/KO IHCs was reduced for mild depolarizations (−45, –43 and −41 mV; p=0.0115, p=0.0295 and p=0.1321, respectively; p=0.0017, p=0.0042 and p=0.0489, without definitive outliers; Mann-Whitney-Wilcoxon test), but comparable to RBE^WT/WT IHCs at stronger depolarizations (−39 mV; p=0.2030, Mann-Whitney-Wilcoxon test). Box plots show 10, 25, 50, 75 and 90^th percentiles with the individual data points overlaid.