Figure 9. Presynaptic function is altered in dfcr IHCs.

I_Ca and exocytic membrane capacitance changes (ΔC_m) were measured in perforated-patch (A–D) and ruptured-patch configurations (4 mm EGTA + 2 mm Ca²⁺ in the pipette, E–H). The extracellular Ca²⁺ was 10 mm to adequately resolve ΔC_m. A, I–V relationship for I_Ca evoked by 10 ms voltage steps from −96.6 mV in perforated-patch recordings (control: n= 23, dfcr: n= 40). B, representative I_Ca and ΔC_m (C_m filtered at 50 Hz) in response to 20 ms depolarization to voltage eliciting peak I_Ca. C, ΔC_m (top) and corresponding I_Ca integral (Q_Ca, bottom) in response to step pulses for the indicated durations. Depolarizations were from −96.6 mV to the voltage eliciting peak I_Ca (between −26.6 and −16.6 mV) for each cell. Data represent grand averages (calculated from the means of the individual cells, n= 26 for dfcr and 15 for control IHCs (p13–19) ± SEM. D, reduced Ca²⁺ efficiency of synchronous exocytosis in dfcr IHCs in response to depolarizations eliciting peak I_Ca in perforated- patch recordings. ΔC_m was normalized to Q_Ca obtained with different stimulus durations in B and C and shown for control and dfcr IHCs (***P < 0.01, by Student's t test). E, I–V relationship for I_Ca evoked by 10 ms voltage steps from −96.2 mV (control: n= 11, dfcr: n= 13) in ruptured-patch recordings. F and G, same as in B and C, but for data obtained with ruptured-patch configuration with 4 mm EGTA and 2 mm Ca²⁺ in the intracellular solution. In F, n= 10 for dfcr and 10 for control IHCs. G and H, tendency towards reduced Ca²⁺ efficiency of synchronous exocytosis was also observed in EGTA-loaded dfcr IHCs. H, same as in D, but for ruptured-patch configuration (n= 10 for control, n= 10 for dfcr).