Absence of voltage-dependent compliance in high-frequency cochlear outer hair cells.

Cochlear outer hair cells are the key element in a mechanical amplification process that enhances auditory sensitivity and tuning in the mammalian inner ear. The electromotility of outer hair cells, that is, their ability to extend or contract at acoustic frequencies, is proposed to be the source of the mechanical amplification. For amplification to take place, some stiffness is required for outer hair cells to communicate force to the organ of Corti, the sensory epithelium of the inner ear. Modulation of this stiffness would be expected to have a significant effect on inner ear function. Outer hair cell compressive stiffness has recently been shown to be dependent on membrane potential, but this has only been demonstrated for cells originating in the apical, low-frequency segment of the cochlea, whereas cochlear amplification is arguably more important in the more basal high-frequency segment. The voltage-dependent compliance (the reciprocal of stiffness) of high-frequency outer hair cells was investigated by two methods in cells isolated from the basal turns of the guinea pig cochlea. In contrast to previous findings, no evidence was found for voltage-dependent changes in compliance. The results call into question the importance of outer hair cell voltage-dependent compliance as a component of cochlear amplification.