Effect of turgor pressure on outer hair cell motility.

The motor in the outer hair cell converts electrical energy directly into mechanical energy. There are two possible mechanisms for such a motor: one depends on changes in the membrane area ("area motor") and the other on changes in the stiffness ("stiffness motor"). These two mechanisms, which are not mutually exclusive, give different predictions on turgor pressure dependence of the amplitude. It was found that an increased pressure shifts the voltage dependence but does not change the amplitude of length changes. This observation is incompatible with a pure stiffness motor model. It was also confirmed that length changes are closely related to charge movements by monitoring the membrane capacitance. It can be concluded that hair cell motility is primarily based on area changes, and not changes in the elastic moduli.