Effects of electrical polarization on inner hair cell receptor potentials

Ac and dc receptor potential components in response to tone-burst stimuli were measured from inner hair cells in the third cochlear turn of the guinea pig. Comparisons were sought between conditions when constant polarizing current was injected into the cell through the recording electrode and when there was no extrinsic current. Hyperpolarization of the cell increased all responses, while depolarization decreased them. The input-output functions were vertically translated by current injection. The extent of translation was a function of current level. In addition, the amount of current-induced change was frequency dependent. Largest changes were seen at low frequencies and the current-induced change tended toward a constant high-frequency asymptote between 1-2 kHz. Changes in the dc response component were considerably in excess of those for the fundamental ac response. The frequency-dependent effects are quantified with the aid of a hair cell circuit model [P. Dallos, Hear. Res. 14, 281-291 (1984)]. It is assumed that the quantity altered by polarizing current (actually by the transmembrane voltage) is the resistance of the cell's basolateral membrane.