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 m
m 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 (
itr) 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
imax,
x1, and α are constants. Curve-fit parameters for the plots shown are for the basal cell and are as follows:
imax = 2031.9 pA,
x1 = 35.3 nm, α = 16.1 nm. For the apical cell, the curve-fit parameters are as follows:
imax = 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.