  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 the frequency dependent activity of prestin. Here we evaluate
complex capacitance of prestin out to 30 kHz and find that its frequency
response determined using this approach coincides with all previous estimates.
We also show that membrane tension has no effect on the frequency response of
prestin, 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 must therefore limit the effectiveness if
prestin in contributing to cochlear amplification at the very high acoustic
frequencies processed by some mammals.
