Figure 3.

MET currents of apical OHCs for control and p.T416K mutant mice. A, MET currents in response to bundle vibration in Tmc1+/+; Tmc2−/− in saline containing 1.5 mm Ca²⁺ (black, gray before and after) and endolymph-like 0.04 mm Ca²⁺ (red); top trace is driving voltage to piezo (smooth curve) superimposed on photodiode signal (noisy gray trace). B, Current-displacement relations evaluated from responses in A for 1.5 mm Ca²⁺ (black) and 0.04 mm Ca²⁺ (red). Lowering external Ca²⁺ increased maximum current I_MAX and fraction on at rest. Dashed curves are fits of current I against displacement x to Boltzmann equation: I = I_MAX/[1 + exp((x1 – x)/a)], where I_MAX = 1.0 nA, a = 9.8 nm, x1 = 29 nm (1.5 Ca²⁺) and I_MAX = 1.43 nA, a = 21 nm, x1 = 6.9 nm (0.04 Ca²⁺). C, MET currents in response to bundle vibration in Tmc1 p.T416K/T416K; Tmc2−/− mice in saline containing 1.5 mm Ca²⁺ (black, gray before and after) and endolymph-like 0.04 mm Ca²⁺ (red); top trace is driving voltage to piezo (smooth curve) superimposed on photodiode signal (noisy gray trace). D, Current-displacement relations evaluated from responses in C for 1.5 mm Ca²⁺ (black) and 0.04 mm Ca²⁺ (red). Dashed curves are fits to Boltzmann equation, where I_MAX = 0.98 nA, a = 10.4 nm, x1 = 23 nm (1.5 Ca²⁺) and I_MAX = 1.56 nA, a = 14.7 nm, x1 = 23.6 nm (0.04 Ca²⁺). Note that in mutant, low Ca²⁺ still increases maximum current but has smaller effect on resting open probability, and no effect on x1, i.e., no shift in the activation curve; holding potential −84 mV. The difference in resting open probability between control, and mutant was not seen in 1.5 mm extracellular Ca²⁺ (see text).