Current noise spectrum and capacitance due to the membrane motor of the outer hair cell: theory.

The voltage-dependent motility of the outer hair cell is based on a membrane motor densely distributed in the lateral membrane. The gating charge of the membrane motor is manifested as a bell-shaped membrane potential dependence of the membrane capacitance. In this paper it is shown that movements of the gating charge should produce a high-pass current noise described by an inverse Lorentzian similar to the one shown by Kolb and Läuger for ion carriers. The frequency dependence of the voltage-dependent capacitance is also derived. These derivations are based on membrane motor models with two or three states. These two models lead to similar predictions on the capacitance and current noise. It is expected that the examination of the spectral properties of these quantities would be a useful means of determining the relaxation time for conformational transitions of the membrane motor.