Figure 1.

Simultaneous recordings of IHC transducer currents and BM displacement from adult gerbil hemicochleae. Tight-seal recordings are made from two IHCs in the apical and basal turns at a holding potential of −70 mV. Basolateral potassium conductances are blocked by 140 mm CsCl in the patch electrodes. The stimulus frequency is 500 Hz. A, B, An Apical-turn IHC (A) and basal-turn IHC (B) are shown. Upward-plotted displacement represents the BM moving toward the scala media, which evokes an increase in inward current (plotted downward). The calibration bars apply to both apical- and basal-turn IHCs. C, Steady-state transducer current, slope (sensitivity), and conductance plotted as a function of BM displacement for 10 cells (5 cells from each turn). The magnitude of base-to-peak current is plotted against corresponding magnitude of base-to-peak BM displacement. An increase in inward current is plotted upward. For the sake of simplicity, the transducer current (i_tr) is fitted with first-order Boltzmann functions (solid lines with open and filled circles), and the slope of the current-fit functions (dashed lines) are plotted for the two cells shown in A and B. Curve fitting was accomplished by using IGORPro (WaveMetrics, Lake Oswego, OR), as follows:

where x is BM displacement and i_max, x₁, and α are constants. Curve-fit parameters for the plots shown are for the basal cell and are as follows: i_max = 2031.9 pA, x₁ = 35.3 nm, α = 16.1 nm. For the apical cell, the curve-fit parameters are as follows: i_max = 2195.2 pA, x₁ = 82.1 nm, α = 34.4 nm. Slope functions are obtained by differentiating the Boltzmann curves. Open and filled symbols represent the apical- and basal-turn IHCs, respectively.