Nonlinear active force generation by cochlear outer hair cell

We analyze the nonlinear behavior of the longitudinal and circumferential c omponents of the active force generated by the outer hair cell wall in resp onse to changes of its transmembrane potential. We treat the material of th e wall as electroelastic, linear orthotropic in terms of strains and as non linear in terms of the transmembrane potential. To describe the nonlinear b ehavior of the active force versus the transmembrane potential, we use two (Boltzmann and simple exponential) types of approximation. We estimate free parameters of these approximations by combining the previously reported pa ssive stiffnesses with the active strains measured in the microchamber expe riment. We analyze the sensitivity of the estimated parameters correspondin g to changes of the cell axial stiffness, a characteristic independently me asured by several groups. We also study the effect of combining the active strains measured in the microchamber experiment with those measured in the whole cell recording experiment. We show agreement between our prediction o f the active force and measurements in the whole cochlea and in isolated ce lls. (C) 1999 Acoustical Society of America. [S0001-4966(99)01104-2].