FREQUENCY-RESPONSE OF MATURE GUINEA-PIG OUTER HAIR-CELLS TO STEREOCILIARY DISPLACEMENT

Outer hair cells (OHC) were isolated from the apical two turns of the guinea-pig cochlea and their hair-bundle stimulated mechanically by a glass probe. In accordance with in vivo data (Dallos, 1985), the resti ng membrane potential was typically -64 mV (N = 200). The maximum ampl itudes of the receptor potentials were between 0.4 and 5.2 mV peak-to- peak, with mean of 1.5 mV +/- 0.9 mV (N = 81). The sensitivity was 0.0 15 mV/nm or 2 mV/deg. The frequency response of the receptor potential followed a first order low-pass filter characteristic with a corner f requency of about 63 Hz. For frequencies up to at least 1.6 kHz, the f requency response of mechanoelectrical transduction was dominated by t he electrical input impedance of the cell. The presence of a single ti me constant in the voltage response to stereociliary deflection implie s that the frequency response of mechanoelectrical transduction far ex ceeds that of the electrical input impedance of the cell; its time con stant must be faster than 100 mu s. Under in vivo conditions, OHC shou ld be capable of providing a sufficiently large receptor potential to supply enough energy for electromechanical feedback.