Outer hair cell electromotility: the sensitivity and vulnerability of the DC component.

A technique was devised in order to study the fast electromechanical length changes of outer hair cells at low stimulus levels. Solitary outer hair cells were drawn into a glass microchamber. Length changes were evoked by the application of transcellular potentials and were detected with a photodiode. The method is non-invasive to the cell and offers superior sensitivity and stability for the recording of cell length changes. The function relating command voltage and cell length (V-delta L) change was determined. A nonlinearity, consisting of a DC component superimposed on the AC response, was shown to be present at the lowest stimulus levels measured. The nonlinearity was sensitive to imposed electrical bias as well as vulnerable to overstimulation. The observations are interpreted in reference to the V-delta L function. A parallel is suggested between the nonlinearity seen in the mechanical response and that observed in the responses of the intact cochlea.