Effectiveness of outer hair cells as cochlear amplifier: In simple model systems.

Cochlear outer hair cells (OHCs) have two mechanosensitive elements: the hair bundle (HB) with mechanotrasducer channels and the piezoelectric lateral wall of the cell body. The present report examines how these elements interact with each other by incorporating OHCs into the simplest local cochlear models. In the frequency range, typically above 1 kHz, where capacitive conductance is greater than the ionic conductance, HB conductance drives the piezoelectric cell body and amplified oscillation by countering viscous drag, whereas the cell body increases its stiffness owing to strain-induced polarization, elevating the resonance frequency. Since HB sensitivity is essential for amplification, the resonance is not pure piezoelectric but semi-piezoelectric. In the lower-frequency range, typically lower than 100 Hz, strain-induced polarization contributes to drag, and the HB sensitivity increases cell body stiffness.