VISCOELASTIC RELAXATION IN THE MEMBRANE OF THE AUDITORY OUTER HAIR CELL

The outer hair cell (OHC) in the mammalian ear has a unique membrane p otential-dependent motility, which is considered to be important for f requency discrimination (tuning), The OHC motile mechanism is located at the cell membrane and is strongly influenced by its passive mechani cal properties. To study the viscoelastic properties of OHCs, we expos ed cells to a hypoosmotic solution for varying durations and then punc tured them, to immediately release the osmotic stress. Using video rec ords of the cells, we determined both the imposed strain and the strai n after puncturing, when stress was reset to zero. The strain data wer e described by a simple rheological model consisting of two springs an d a dashpot, and the fit to this model gave a time constant of 40 +/- 19 s for the relaxation (reduction) of tension during prolonged strain . For time scales much shorter or longer than this, we would expect es sentially elastic behavior. This relaxation process affects the membra ne tension of the cell, and because it has been shown that membrane te nsion has a modulatory role in the OHC's motility, this relaxation pro cess could be part of an adaptation mechanism, with which the motility system of the OHC can adjust to changing conditions and maintain opti mum membrane tension.