OUTER HAIR CELL LENGTH CHANGES IN AN EXTERNAL ELECTRIC-FIELD .2. THE ROLE OF ELECTROKINETIC FORCES ON THE CELL-SURFACE

An isolated cochlear outer hair cell can elongate or shorten when elec trically stimulated, as discovered by Brownell et al. [Science 227, 19 4-196 (1985)]. In their experiments, the cylindrically shaped cell was fixed at one end, and was positioned between two electrodes which Lie on the cell axis, but were far from the cell (transcellular stimulati on). A model is developed to predict the component of the cell's elong ation which arises from only electrokinetic phenomena. Outside the cel l, electro-osmosis produces a drag on the lateral wall which almost ex actly balances the electrophoretic force. In contrast to previous theo ries, we find that the electrokinetic response is governed by the free end of the cell, not the lateral wall. If the surface charge density of the free end lies between -0.004 and 0.07 C/m(2) (corresponding to the zeta potential between -5 and -60 mV), then our model predicts elo ngations that are comparable in magnitude to experimentally measured v alues. (C) 1995 Acoustical Society of America.