Figure 1.
Figure 1. Effects of GsMTx-4 on MT currents in OHCs. (A) MT currents evoked by sinusoidal fluid-jet stimuli before (black), during (red trace), and after (gray) perfusion with 1.0 µM GsMTx-4 toxin. Shown above are the photodiode signals denoting hair bundle motion for the three conditions. (B) I-X relationships from traces in A. MT current over the first cycle of the response plotted against bundle displacement is shown. Blue lines are fits with single-state Boltzmann: I = Imax/(1 + exp(−((X − X0.5)/Xs))), where Imax is maximum current, X0.5 is half-activation displacement, and Xs is slope. Parameter values for control: Imax = 0.71 nA, X0.5 = 26 nm, and Xs = 20 nm; with toxin: Imax = 0.15 nA, X1 = −1 nm, and X2 = 13 nm. (C) Reversed stimulus–polarity mechanosensitive currents evoked by sinusoidal fluid-jet stimuli before, during (red trace), and after perfusion with 5.0 µM toxin. Recordings on apical OHCs in a Tmc1dn/dn Tmc2−/− mutant. The driving voltage to the fluid-jet piezoelectric disk is shown above with the calibration taken from that in A. (D) Dose–response relationships for the effects of toxin on MT currents of wild-type OHCs at the apex (closed circles; P4–P7), base (open circles; P3), and apex of Tmc1dn/dn Tmc2−/− (crosses; P3–P6). Error bars indicate mean ± SEM. Number of cells: apex, 3–12; base, 3–8; Tmc1dn/dn Tmc2−/− double mutants, 4–6. Smooth curve is a Hill equation fitted to all points with IC50 = 0.65 ± 0.1 µM and nH = 0.92. (E) Effects of toxin on I-V relationship. OHC stimulated with sinusoidal fluid jet superimposed on a voltage ramp from −150 to 100 mV, in the absence and presence (red trace) of 1 µM toxin. (F) I-V relationships from traces in E, showing that the block is relieved at positive potentials. Unless otherwise stated (as in D), all measurements were performed on P5 apical OHCs.

Effects of GsMTx-4 on MT currents in OHCs. (A) MT currents evoked by sinusoidal fluid-jet stimuli before (black), during (red trace), and after (gray) perfusion with 1.0 µM GsMTx-4 toxin. Shown above are the photodiode signals denoting hair bundle motion for the three conditions. (B) I-X relationships from traces in A. MT current over the first cycle of the response plotted against bundle displacement is shown. Blue lines are fits with single-state Boltzmann: I = Imax/(1 + exp(−((X − X0.5)/Xs))), where Imax is maximum current, X0.5 is half-activation displacement, and Xs is slope. Parameter values for control: Imax = 0.71 nA, X0.5 = 26 nm, and Xs = 20 nm; with toxin: Imax = 0.15 nA, X1 = −1 nm, and X2 = 13 nm. (C) Reversed stimulus–polarity mechanosensitive currents evoked by sinusoidal fluid-jet stimuli before, during (red trace), and after perfusion with 5.0 µM toxin. Recordings on apical OHCs in a Tmc1dn/dn Tmc2−/− mutant. The driving voltage to the fluid-jet piezoelectric disk is shown above with the calibration taken from that in A. (D) Dose–response relationships for the effects of toxin on MT currents of wild-type OHCs at the apex (closed circles; P4–P7), base (open circles; P3), and apex of Tmc1dn/dn Tmc2−/− (crosses; P3–P6). Error bars indicate mean ± SEM. Number of cells: apex, 3–12; base, 3–8; Tmc1dn/dn Tmc2−/− double mutants, 4–6. Smooth curve is a Hill equation fitted to all points with IC50 = 0.65 ± 0.1 µM and nH = 0.92. (E) Effects of toxin on I-V relationship. OHC stimulated with sinusoidal fluid jet superimposed on a voltage ramp from −150 to 100 mV, in the absence and presence (red trace) of 1 µM toxin. (F) I-V relationships from traces in E, showing that the block is relieved at positive potentials. Unless otherwise stated (as in D), all measurements were performed on P5 apical OHCs.

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