Figure 6. Ca²⁺ buffers do not prevent inactivation of the Ca²⁺ channels.

A, Ca²⁺ currents recorded from adult basal IHCs in the presence of 1 mm EGTA (black), 0.1 mm BAPTA (dark grey) or 5 mm BAPTA (grey) in response to a 1 s voltage step to −11 mV from a holding potential of −81 mV. Fits through the data were obtained using a double exponential equation. The fitting parameters are: 1 mm EGTA τ_fast 52 ms, τ_slow 435 ms; 0.1 mm BAPTA τ_fast 54 ms, τ_slow 1181 ms, 5 mm BAPTA τ_fast 51 ms, τ_slow 589 ms. Cell properties were: 1 mm EGTA (P25) C_m 12.2 pF, R_s 4.7 MΩ, g_leak 0.8 nS; 0.1 mm BAPTA (P69) C_m 10.5 pF, R_s 5.4 MΩ, g_leak 0.9 nS; 5 mm BAPTA (P69) C_m 10.4 pF, R_s 4.2 MΩ, g_leak 0.6 nS. B, Average percentage of I_Ca inactivation using 1 mm EGTA (P25 basal IHCs) and different BAPTA (0.1, 0.3, 1 and 5 mm) concentrations (P69 basal IHCs). C and D, fast (τ_fast) and slow (τ_slow) time constants obtained by fitting the time course of I_Ca inactivation using a double exponential. Number of cells in B–D is shown above each column.