Fluctuation of motor charge in the lateral membrane of the cochlear outer hair cell.

Functioning of the membrane motor of the outer hair cell is tightly associated with transfer of charge across the membrane. To obtain further insights into the motor mechanism, we examined kinetics of charge transfer across the membrane in two different modes. One is to monitor charge transfer induced by changes in the membrane potential as an excess membrane capacitance. The other is to measure spontaneous flip-flops of charges across the membrane under voltage-clamp conditions as current noise. The noise spectrum of current was inverse Lorentzian, and the capacitance was Lorentzian, as theoretically expected. The characteristic frequency of the capacitance was approximately 10 kHz, and that for current noise was approximately 30 kHz. The difference in the characteristic frequencies seems to reflect the difference in the modes of mechanical movement associated with the two physical quantities.