Abstract
Outer hair cell (OHC) nonlinear capacitance (NLC) represents voltage sensor charge movements of prestin (SLC26a5), the protein responsible for OHC electromotility. Previous measures of NLC frequency response have employed methods which did not assess the influence of dielectric loss (sensor charge movements out of phase with voltage) that may occur, and such loss conceivably may influence prestin’s frequency dependent activity. Here we evaluate prestin’s complex capacitance out to 30 kHz and find that prestin’s frequency response determined using this approach coincides with all previous estimates. We also show that membrane tension has no effect on prestin’s frequency response, despite substantial shifts in its voltage operating range, indicating that prestin transition rate alterations do not account for the shifts. The magnitude roll-off of prestin activity across frequency surpasses the reductions of NLC caused by salicylate treatments that are known to abolish cochlear amplification. Such roll-off likely limits the effectiveness of prestin in contributing to cochlear amplification at the very high acoustic frequencies processed by some mammals.
Highlights
Outer hair cell (OHC) nonlinear capacitance (NLC) represents voltage sensor charge movements of prestin (SLC26a5), the protein responsible for OHC electromotility
Will an assessment of NLC based on measures of complex NLC alter our current view, as suggested[18], and can turgor pressure, normally present in the OHC19, with its effect on membrane tension be influential? Our observations indicate that the bulk of sensor charge movement is in phase with voltage, while the resistive component is relatively small
We previously evaluated OHC macro-patch NLC frequency dependence utilizing a dual-sine methodology that worked on extracted prestin displacement currents[13]
Summary
Outer hair cell (OHC) nonlinear capacitance (NLC) represents voltage sensor charge movements of prestin (SLC26a5), the protein responsible for OHC electromotility. Previous measures of NLC frequency response have employed methods which did not assess the influence of dielectric loss (sensor charge movements out of phase with voltage) that may occur, and such loss conceivably may influence prestin’s frequency dependent activity. We evaluate patch admittance to provide estimates of complex capacitance representing charge movements both in phase and 90° out of phase with AC voltage excitation We compare such data to previously obtained measures of OHC NLC frequency response[13,14], and report on the effects of membrane tension[15,16,17] on the frequency response of complex NLC. Magnitude estimates of complex NLC are comparable to those measured with other methods[13,14], being unusually low pass in nature (non-Lorentzian) and indicating that the absolute movement of prestin charge that drives electromotility (eM)[20,21] is unlikely to extend with high fidelity to the very high acoustic frequencies (60–160 kHz) detected by some mammals
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