Figure 4.

Resting potentials and membrane time constants (τ_m) in gerbil OHCs. (A) Voltage responses to current steps in an apical OHC with the hair bundle exposed to 1.3 mM Ca²⁺, 0.02 mM Ca²⁺ and 0.2 mM DHS + 1.3 mM Ca²⁺. Note low Ca²⁺ depolarizes the OHC and reduces τ_m. Blocking MT channels with DHS hyperpolarizes the OHC and increases τ_m. τ_m was obtained by fitting voltage onsets (dashed lines) with: V = A(1 − exp (−t/τ_m)), where τ_m = 2.3 ms (1.3 Ca²⁺), 0.6 ms (0.02 Ca²⁺), 5.3 ms (1.3 Ca²⁺ + DHS). (B) Collected resting potentials (mean ± SEM) from apical OHCs with bundles exposed to 1.3 mM Ca²⁺ (control, n = 15; wash, n = 14), 0.02 mM Ca²⁺ (n= 5) and 0.2 mM DHS + 1.3 mM or 0.02 mM Ca²⁺ (n = 9). (C) Collected corner frequencies (F_0.5 = 1/2πτ_m; mean ± SEM) calculated from τ_m measurements as in (A), numbers of measurements in each category as in (B). (D) Voltage responses to current steps with hair bundles perfused with 0.02 mM Ca²⁺ for three gerbil cochlear locations with different CFs. τ_m obtained from fits (dashed lines) and CF were: 0.67 ms (0.35 kHz); 0.23 ms (0.9 kHz); 0.10 ms (2.5 kHz).