  Electromotility of outer hair cells (OHCs) has been extensively studied with
in vitro experiments because of its physiological significance in the cochlear
amplifier, which provides the exquisite sensitivity and frequency selectivity
of the mammalian ear. However, these studies have been performed largely under
load-free conditions or with static load, while these cells function in vivo in
a dynamic environment, receiving electrical energy to enhance mechanical
oscillation in the inner ear. This gap leaves uncertainties in addressing a key
issue, how much mechanical energy an OHC provides. The present report is an
attempt of bridging the gap by introducing a simple one-dimensional model for
electromotility of OHC in a dynamic environment. This model incorporates a
feedback loop involving the receptor potential and the mechanical load on OHC,
and leads to an analytical expression for the membrane capacitance, which
explicitly describes the dependence on the elastic load, viscous drag, and the
mass. The derived equation of motion was examined in a mass-less model system
with realistic parameter values for OHC. It was found that viscous drag is more
effective than elastic load in enhancing the receptor potential that drives the
cell. For this reason, it is expected that OHCs are more effective in
counteracting viscous drag than providing elastic energy to the system.
