Elasticity and active force generation of cochlear outer hair cells

The cochlear outer hair cell is described by a cylindrical membrane model, characterized by area and shear moduli for a passive elastic element and an active tension element dependent on the membrane potential. In passive experiments, these moduli are determined from the pressure-strain relations. The area modulus obtained is 0.07 N m-1, similar to a lipid bilayer and the shear modulus is 0.007 N m-1. These moduli combined with previous active experiments show that the active tension is nearly isotropic and is about 1.6 x 10(-2) N m-1 V-1, resulting in a 0.5 nN/mV force per cell. This implies that the receptor potential for acoustical stimulation produces an active force comparable to the acoustic force applied to the basilar membrane per outer hair cell. This finding supports the hypothesis that the outer hair cell acts as feedback motor in the fine tuning mechanism of the mammalian ear.