A membrane bending model of outer hair cell electromotility

We propose a new mechanism for outer hair cell electromotility based on ele ctrically induced localized changes in the curvature of the plasma membrane (flexoelectricity). Electromechanical coupling in the cell's lateral wall is modeled in terms of linear constitutive equations for a flexoelectric me mbrane and then extended to nonlinear coupling based on the Langevin functi on. The Langevin function, which describes the fraction of dipoles aligned with an applied electric field, is shown to be capable of predicting the el ectromotility voltage displacement function. We calculate the electrical an d mechanical contributions to the force balance and show that the model is consistent with experimentally measured values for electromechanical proper ties. The model rationalizes several experimental observations associated w ith outer hair cell electromotility and provides for constant surface area of the plasma membrane. The model accounts for the isometric force generate d by the cell and explains the observation that the disruption of spectrin by diamide reduces force generation in the cell. We discuss the relation of this mechanism to other proposed models of outer hair cell electromotility . Our analysis suggests that rotation of membrane dipoles and the accompany ing mechanical deformation may be the molecular mechanism of electromotilit y.