Figure 4. I_Ca in immature IHCs.

A and B, inward I_Ca recordings from a P6 IHC during superfusion of 1.3 mm (A) and 5 mm (B) extracellular Ca²⁺, in response to voltage steps from −113 mV to more depolarized potentials in 5 or 10 mV increments. The holding potential was −103 mV. A schematic representation of the voltage protocol is shown above the current traces. For clarity, only some of the traces are shown and some of the potentials are shown next to the traces. Residual capacitative transients have been blanked. The extracellular solution contained 30 mm TEA and 200 nm TTX. Currents in A and B are averages from six and four repetitions, respectively. The recording conditions were: C_m 7.7 pF; R_s 4.8 MΩ; g_leak 1.3 nS; temperature 37°C. C, average peak I-V curves for seven P6-P7 IHCs during extracellular superfusion of 1.3 (•) and 5 mm (○) Ca²⁺ (including the cell shown in A and B). The continuous lines are fits calculated using eqn (1) (see text for details). The fitting parameters are: in 1.3 mm Ca²⁺, g_max 7.0 nS, V_rev 45 mV, V_1/2−32.8 mV, S 6.9 mV; in 5 mm Ca²⁺, g_max 13.0 nS, V_rev 45 mV, V_1/2−26.7 mV, S 6.9 mV. D, time constants of activation for I_Ca measured in the same seven IHCs.