A and B, transducer currents recorded from an apical P7 OHC before (A) and during (B) the superfusion of 50 μm dihydrostreptomycin (DHS) when sinusoidal force stimuli of 45 Hz were used. The cell was held at −84 mV and the membrane potential was stepped, in 20 mV increments, between −144 mV and +96 mV. For clarity only responses to every other voltage step are shown. Driver voltage (DV, amplitude 35 V) to the fluid jet is shown above the traces. Positive DVs are excitatory. Membrane potentials are shown next to some of the traces. Recordings in A and B are the average of 4 repetitions and are offset so that the zero-transducer current levels (responses to inhibitory stimuli) are equally spaced. Cm 6.0 pF; Rs 0.8 MΩ. C, average normalized current–voltage curves for the control transducer currents (n = 30) and the current recorded during the superfusion of 3 μm (n = 9), 10 μm (n = 8) and 50 μm (n = 13) DHS (1.3 mm extracellular Ca2+), when both sine waves and voltage step stimuli were used. Note that the currents have been normalized to the maximal current recorded at +96 mV (Control: 878 ± 36 pA; 3 μm: 980 ± 55 pA; 10 μm: 708 ± 73 pA; 50 μm: 924 ± 61 pA). D, dose–response curves for the block of the transducer current by DHS at three different membrane potentials obtained from 35 apical-coil OHCs. Continuous lines are the fits through the data using . Fit at −164 mV: half blocking concentration (KD) = 11.4 ± 0.6 μm, Hill coefficient (nH) = 0.90 ± 0.03 (number of measurements from left to right: 1, 10, 9, 4, 1, 10); −84 mV: KD= 7.0 ± 0.2 μm, nH= 0.96 ± 0.03 (2, 3, 12, 9, 4, 8, 1, 5, 13, 6, 1); −44 mV: KD= 21.2 ± 0.9 μm, nH= 0.96 ± 0.04 (number of measurements as for −84 mV). E, average KD and nH plotted as a function of the membrane potential. Number of measurements: 35 at −164 mV; 50 at −144 mV and −24 mV and 64 for all other potentials tested. The fit through the KD data points is according to with: ΔE =E2−E1= 4.63 kT, Δδ=δ2−δ1= 0.91, Eb=−8.27 kT and δb= 0.79.