Scope with a 40?lens was used to observe cells during voltage clamping. Experiments were performed at room temperature. Direct-current (DC) TAPI-2 site voltages were corrected for series-resistance (Rs) effects, and AC currents were corrected for system roll-off, as previously described (19,20). Series and membrane resistance determined from step analysis were similar for the two chloride groups. For the 140 mM Cl group, Rs ?9.37 5 0.31 MU and Rm ?337 5 45.9 MU for n ?21 OHCs; for the 1 mM Cl group, Rs ?8.39 5 0.47 MU and Rm ?365 5 40.5 MU for n ?6 OHCs. Fig. 5, G and H, shows that our measurement system, after corrections for Rs effects, is flat out to 5 kHz, within which bandwidth our data arise (see the Appendix2552 Biophysical Journal 110, 2551?561, June 7,Chloride Controls Prestin KineticsFIGURE 1 Stimulus and analysis paradigms. (A) Traces of voltage protocol. Step voltages (?60 mV to ?00 mV by 20 mV increments) were delivered for 700 ms followed by a return to a holding potential of 0 mV for 40 ms. Superimposed on the steps were summed discrete dual-sine frequencies 655 ms in duration (see Materials and Methods). (B) Elicited currents (offset for easy visualization), AC and step-induced, were used to extract capacitance and integrated charge movements (dashed ovals), respectively. (C) Averaged NLC traces of OHCs with intracellular chloride clamped to 1 or 140 mM chloride. NLC was estimated from the latter half of the dual-sine stimulation duration. (D and E) Corresponding displacement currents extracted by linear capacitive current subtraction (D) and extracted Q-V curves (E) at 1 mM and 140 mM chloride conditions for an equivalent interrogation time based on fits of NLC with Eq. 1 (blue traces) or on fits of integrated off charge with Eq. 2 (red traces) give comparable results, as expected (see Materials and Methods for details). To see this figure in color, go online.changes in specific membrane capacitance generated by prestin state transitions (23). The occupancy of prestin in the expanded state contributes 140 zeptofarads/motor (dCsa) to the linear capacitance, producing an apparent voltage-dependent change in linear capacitance at hyperpolarized levels (23,24). This equation is called the two-state-Csa equation.tive plus a linear capacitance (26,27). Here, Q-V curves were fit to the integral of Eq. 1 with respect to Vm, yieldingQtot ?Cm ?Qmaxze b DCsa ?Clin ; 2 ?kT ? ?b?? ?b? ?(1)Qmax ?b ?Clin ? ?U ?b?b? DCsa ?log ?1???off: ze=kT(2)whereb ?expze kTU and U ?Vh ?Vm :Qmax is the maximum nonlinear charge moved, Vh is the voltage at peak capacitance or, equivalently, at half-maximum sensor charge transfer, Vm is the membrane potential, z is valence, e is the electron charge, k is Boltzmann’s constant, and T is absolute temperature. Clin is defined as the linear capacitance of the membrane when all prestin motors are in their compact state, the minimum membrane capacitance evident at depolarized voltages; DCsa is the maximum increase in capacitance that occurs when all prestin motors change from the compact to the expanded state, each motor contributing a unit response of dCsa. From such fits, voltage-dependent NLC (Cv) is calculated from estimates of Qmax, i.e., Cv ?Qmax/(4 kT/ze) (25). To confirm AC SIS3 web admittance estimates of sensor Qmax, we integrated capacitive currents evoked at the end of voltage steps (exponentially decaying currents of each trace, with the baseline set to current relaxations at 20 ms). Residual ionic currents that r.Scope with a 40?lens was used to observe cells during voltage clamping. Experiments were performed at room temperature. Direct-current (DC) voltages were corrected for series-resistance (Rs) effects, and AC currents were corrected for system roll-off, as previously described (19,20). Series and membrane resistance determined from step analysis were similar for the two chloride groups. For the 140 mM Cl group, Rs ?9.37 5 0.31 MU and Rm ?337 5 45.9 MU for n ?21 OHCs; for the 1 mM Cl group, Rs ?8.39 5 0.47 MU and Rm ?365 5 40.5 MU for n ?6 OHCs. Fig. 5, G and H, shows that our measurement system, after corrections for Rs effects, is flat out to 5 kHz, within which bandwidth our data arise (see the Appendix2552 Biophysical Journal 110, 2551?561, June 7,Chloride Controls Prestin KineticsFIGURE 1 Stimulus and analysis paradigms. (A) Traces of voltage protocol. Step voltages (?60 mV to ?00 mV by 20 mV increments) were delivered for 700 ms followed by a return to a holding potential of 0 mV for 40 ms. Superimposed on the steps were summed discrete dual-sine frequencies 655 ms in duration (see Materials and Methods). (B) Elicited currents (offset for easy visualization), AC and step-induced, were used to extract capacitance and integrated charge movements (dashed ovals), respectively. (C) Averaged NLC traces of OHCs with intracellular chloride clamped to 1 or 140 mM chloride. NLC was estimated from the latter half of the dual-sine stimulation duration. (D and E) Corresponding displacement currents extracted by linear capacitive current subtraction (D) and extracted Q-V curves (E) at 1 mM and 140 mM chloride conditions for an equivalent interrogation time based on fits of NLC with Eq. 1 (blue traces) or on fits of integrated off charge with Eq. 2 (red traces) give comparable results, as expected (see Materials and Methods for details). To see this figure in color, go online.changes in specific membrane capacitance generated by prestin state transitions (23). The occupancy of prestin in the expanded state contributes 140 zeptofarads/motor (dCsa) to the linear capacitance, producing an apparent voltage-dependent change in linear capacitance at hyperpolarized levels (23,24). This equation is called the two-state-Csa equation.tive plus a linear capacitance (26,27). Here, Q-V curves were fit to the integral of Eq. 1 with respect to Vm, yieldingQtot ?Cm ?Qmaxze b DCsa ?Clin ; 2 ?kT ? ?b?? ?b? ?(1)Qmax ?b ?Clin ? ?U ?b?b? DCsa ?log ?1???off: ze=kT(2)whereb ?expze kTU and U ?Vh ?Vm :Qmax is the maximum nonlinear charge moved, Vh is the voltage at peak capacitance or, equivalently, at half-maximum sensor charge transfer, Vm is the membrane potential, z is valence, e is the electron charge, k is Boltzmann’s constant, and T is absolute temperature. Clin is defined as the linear capacitance of the membrane when all prestin motors are in their compact state, the minimum membrane capacitance evident at depolarized voltages; DCsa is the maximum increase in capacitance that occurs when all prestin motors change from the compact to the expanded state, each motor contributing a unit response of dCsa. From such fits, voltage-dependent NLC (Cv) is calculated from estimates of Qmax, i.e., Cv ?Qmax/(4 kT/ze) (25). To confirm AC admittance estimates of sensor Qmax, we integrated capacitive currents evoked at the end of voltage steps (exponentially decaying currents of each trace, with the baseline set to current relaxations at 20 ms). Residual ionic currents that r.
