Figure 13.

Mechanotransducer currents in Ptprq-TM-KO outer hair cells. Transducer currents recorded in basal-coil OHCs from a heterozygous Ptprq-TM-KO mouse (a, c, e, g) and a homozygous Ptprq-TM-KO mouse (b, d, f, h). a, b, Transducer currents recorded at a holding potential of -104 and +96 mV by applying sinusoidal force stimuli of 45 Hz. The driver voltage signal (DV) (amplitude, 35 V) to the fluid jet is shown above each trace. Positive deflections are excitatory. c, d, The time course of onset adaptation to an excitatory step displacement at -84 mV (top panels). Note the difference in the driver voltages applied. Fitted time constants for onset adaptation are as follows: c, 0.34 and 16.1 msec; d, 0.39 and 12.3 msec. Bottom panels show the transducer current in response to a negative stimulus at -84 mV. After termination of the inhibitory stimulus the transducer current shows evidence of rebound adaptation. Fitted time constants for the rebound adaptation are as follows: c, 0.34 and 16.2 msec; d, 0.54 and 16.3 msec. e, f, The time course of the transducer current elicited by excitatory (top panels) and inhibitory (bottom panels) bundle displacements at +86 mV. Note the absence of onset and rebound adaptation. a, c, e, P7 OHC: C_m 6.9 pF; R_s 2.4 MΩ; b, d, f, P7 OHC: C_m 6.7 pF; R_s 3.0 MΩ. All responses shown are single traces. g, h, Normalized peak transducer current as a function of bundle displacement. Zero current is set as the holding current when the force stimulus closes most transducer channels. Smooth curves are second-order Boltzmann functions: I = I_max /(1 + exp(a₂ (x₂ - x))^*(1 + exp(a₁(x₁ - x)))). g, At -84 mV, I_max = -732 pA, a₁ = 0.06 nm^-1, a₂ = 0.04 nm^-1, x₁ = 26 nm, x₂ = 35 nm; at +86 mV, I_max = 810 pA, a₁ = 0.12 nm^-1, a₂ = 0.02 nm ^-1, x₁ = 7 nm, x₂ = 14 nm. P7 OHC: C_m 7.0 pF; R_s 1.4 MΩ. Bundle height 4 μm; bundle width 8 μm. h, At -84 mV, I_max = -211 pA, a₁ = 0.10 nm^-1, a₂ = 0.054 nm ^-1, x₁ = -32nm, x₂ = 41 nm; at +86 mV, I_max = 316 pA, a₁ = 0.15nm ^-1, a₂ = 0.035 nm ^-1, x₁ = -76 nm, x₂ = 24 nm. P7 OHC: C_m 6.8 pF; R_s 2.5 MΩ. Bundle height 3.5 μm; bundle width 6 μm.