Two models of outer hair cell stiffness and motility

Cochlear outer hair cells change their axial dimension and theiraxial stiff ness when their membrane potential is altered. These changes appear to be h ighly correlated. Because of this, we endeavored to produce models that wou ld yield both phenomena via a single mechanism. True models are proposed. I n one, it is assumed that elementary motor molecules can be in either of tw o conformational states, these having different physical lengths and stiffn esses. The state of the molecule is taken to be a stochastic function of me mbrane potential and is expressed by a Boltzmann relationship. In the other model, a similar dependence is assumed to occur between membrane potential and stiffness, but no dimensional change isassigned to the molecule. Lengt h changes carl be had by preloading the cell. We show that either general m odel can produce realistic length and stiffness changes with an appropriate selection of parameters. One particular realization of the first model is proposed as an example. In this-the boomerang model-the molecule is assumed to be L-shaped, with two different angles between the two legs representin g the conformational states. Finally, the behavior of the model is compared with available data when the voltage stimulus comprises a brief sinusoid u pon a DC pedestal.