ELECTROMOTILE RESPONSES AND FREQUENCY TUNING OF ISOLATED OUTER HAIR-CELLS OF THE GUINEA-PIG COCHLEA

Isolated outer hair cells (OHC) of the guinea pig cochlea were exposed to external alternating electric fields parallel to the longitudinal axis of the cells. This resulted in oscillations of the cells' length that were measured photo-electrically using a ratiometric light amplif ier. At 5 Hz and elongations up to 300 nm, amplitude of the cell lengt h during oscillation was a linear function of the amplitude of the sin usoidal electric field. When increasing the stimulus frequency up to 3 2 kHz, OHC length changes followed the stimulus cycle-by-cycle. Oscill ations at frequencies above 32 kHz escaped the experimental approach b y their small amplitudes and could not be excluded. The frequency depe ndence of the motile response measured at 5-12 000 Hz had low-pass fil ter characteristics in cells of the second, third and fourth turns of the cochlea. However, frequency tuning of the motile response was abse nt in each OHC and systematic differences between different turns were not observed.