Evidence of Piezoelectric Resonance in Isolated Outer Hair Cells

Abstract

Our results demonstrate high-frequency electrical resonances in outer hair cells (OHCs) exhibiting features analogous to classical piezoelectric transducers. The fundamental (first) resonance frequency averaged f(n) approximately 13 kHz (Q approximately 1.7). Higher-order resonances were also observed. To obtain these results, OHCs were positioned in a custom microchamber and subjected to stimulating electric fields along the axis of the cell (1-100 kHz, 4-16 mV/80 microm). Electrodes embedded in the side walls of the microchamber were used in a voltage-divider configuration to estimate the electrical admittance of the top portion of the cell-loaded chamber (containing the electromotile lateral wall) relative to the lower portion (containing the basal plasma membrane). This ratio exhibited resonance-like electrical tuning. Resonance was also detected independently using a secondary 1-MHz radio-frequency interrogation signal applied transversely across the cell diameter. The radio-frequency interrogation revealed changes in the transverse electric impedance modulated by the axial stimulus. Modulation of the transverse electric impedance was particularly pronounced near the resonant frequencies. OHCs used in our study were isolated from the apical region of the guinea pig cochlea, a region that responds exclusively to low-frequency acoustic stimuli. In this sense, electrical resonances we observed in vitro were at least an order of magnitude higher (ultrasonic) than the best physiological frequency of the same OHCs under acoustic stimuli in vivo. These resonance data further support the piezoelectric theory of OHC function, and implicate piezoelectricity in the broad-band electromechanical behavior of OHCs underlying mammalian cochlear function.

Dielectric Properties of Yeast Cells Expressed With the Motor Protein Prestin

“…Note that there is a rather pronounced hump, which peaks around 25 kHz. The data in Figure 5 are especially interesting, because they correlates with observations of piezoelectric resonances in outer hair cells that have been isolated from the cochlea [22]. In particular, measurements of the ac admittance versus frequency of an OHC show a peak at around 10 kHz.…”

“…Moreover, the observed correlation between NLC and electromotility suggests that dielectric spectroscopy, which probes total capacitance versus frequency, may potentially be used as a noninvasive probe of cells that have been genetically modified to express prestin. Of particular interest, for example, is a comparison to recent observations [22] of frequency-dependent electrical resonances in OHCs, isolated from the apical turn of the cochlea, exhibiting features analogous to classical piezoelectric transducers.…”

Cochlear Outer Hair Cell Motility

“…In this case, complex modes of excitation might occur. Some of these modes have been explored by placing OHCs in a custom microchamber that allows the top and bottom of the lateral membrane to be stimulated extracellular current at 1-100 kHz (259). The findings show complex piezoelectric resonant modes of the cell where transverse electrical resonances become modulated by axial forces.…”

Detection of pulse trains in the electrically stimulated cochlea: Effects of cochlear health

“…First, there is a potential for electrical stimulation of a cochlear implant to induce a traveling wave in the basilar membrane by causing contraction of outer hair cells or by a piezoelectric-like effect (Brownell et al, 1985;Rabbitt et al, 2005). If inner hair cells are intact, these phenomena could produce hearing mediated by stereocilia deflection and transmitter release similar to that produced by acoustic stimulation.…”