Figure 1.

Ca²⁺ channel currents carried by Ba²⁺ (10 mm) in mouse outer hair cells around and after the onset of hearing. A, Peak inward I_Ba (single trace) elicited by a step depolarization from −70 to 0 mV for 8 ms in a P12 apical OHC. Capacitive current transients attributable to prestin action at the start and end of the current response were cut off. Dashed line, Zero current trace. B, Corresponding I–V. C, I_Ba I–V for another apical OHC (P12) before (control) and during superfusion with 5 μm Bay K 8644 indicates that I_Ba is an L-type current. D, E, Non-inactivating peak current trace of an apical OHC at P19 in response to a long inactivation protocol (single trace; command voltages are given, D) and corresponding steady-state I–V (E) at the end of the first 400 ms depolarizing pulse in Tris-lactobionate solution. Large current transients in A and D were attributable to the nonlinear capacitance of OHCs. F, Developmental upregulation and downregulation of peak I_Ba as a function of age. Data for P1–P8 were adopted from Michna et al. (2003). Number of cells for ages older than P8 are as follows: P9, 4; P10, 2; P11, 2; P12, 4; P13, 1; P15, 2; and P19, 3. OHCs older than P8 were from apical half-turns, except two medial OHCs at P15.