  The outer hair cell (OHC) membrane harbors a voltage-dependent protein,
prestin (SLC26a5), in high density, whose charge movement is evidenced as a
nonlinear capacitance (NLC). NLC is bell-shaped, with its peak occurring at a
voltage, Vh, where sensor charge is equally distributed across the plasma
membrane. Thus, Vh provides information on the conformational state of prestin.
Vh is sensitive to membrane tension, shifting to positive voltage as tension
increases and is the basis for considering prestin piezoelectric (PZE). NLC can
be deconstructed into real and imaginary components that report on charge
movements in phase or 90 degrees out of phase with AC voltage. Here we show in
membrane macro-patches of the OHC that there is a partial trade-off in the
magnitude of real and imaginary components as interrogation frequency
increases, as predicted by a recent PZE model (Rabbitt, 2020). However, we find
similar behavior in a simple kinetic model of prestin that lacks piezoelectric
coupling, the meno presto model. At a particular frequency, Fis, the complex
component magnitudes intersect. Using this metric, Fis, which depends on the
frequency response of each complex component, we find that initial Vh
influences Fis; thus, by categorizing patches into groups of different Vh,
(above and below -30 mV) we find that Fis is lower for the negative Vh group.
We also find that the effect of membrane tension on complex NLC is dependent,
but differentially so, on initial Vh. Whereas the negative group exhibits
shifts to higher frequencies for increasing tension, the opposite occurs for
the positive group. Despite complex component trade-offs, the low-pass roll-off
in absolute magnitude of NLC, which varies little with our perturbations and is
indicative of diminishing total charge movement, poses a challenge for a role
of voltage-driven prestin in cochlear amplification at very high frequencies.
