Effect of voltage-dependent membrane properties on active force generation in cochlear outer hair cell.

A computational model is proposed to analyze the active force production in an individual outer hair cell (OHC) under high-frequency conditions. The model takes into account important biophysical properties of the cell as well as constraints imposed by the surrounding environment. The biophysical properties include the elastic, piezoelectric, and viscous characteristics of the cell wall. The effect of the environment is associated with the stiffness of the constraint and the drag forces acting on the cell due to the interaction with the external and internal viscous fluids. The study concentrated on a combined effect of the transmembrane potential, frequency, and stiffness of the constraints. The effect of the voltage-dependent stiffness of the cell was particularly investigated and it was found to be twofold. First, it results in higher sensitivity and nonlinearity of the OHC active force production in the physiological range. Second, it determines smaller active forces in the hyperpolarization range. The resonant properties of the active force as functions of voltage and the constraint stiffness were also analyzed. The obtained results can be important for a better understanding of the OHC active force production and the contribution of cell electromotility to the cochlear amplification, sensitivity, and nonlinearity.