Potassium currents underlying the oscillatory response in hair cells of the goldfish sacculus

1. Ionic currents underlying the oscillatory response of membrane potential were studied in oscillatory-type hair cells isolated from the goldfish sacculus with the whole-cell recording method using a patch pipette. 2. Bath application of 4-aminopyridine (4-AP; 10 mM) reversibly produced moderate depolarization of the resting potential along with complete suppression of the oscillatory response. Sustained injection of a small depolarizing current also suppressed the oscillatory response. 3. A 4-AP-sensitive atypical A-type K+ current which had a high threshold voltage for inactivation (I-A(H)) was found to be a major outward current underlying the oscillatory response. 4. I-A(H) was activated with a time constant of 0.4-10 ms and was inactivated slowly with a time constant of 0.6-2s. I-A(H) activation and inactivation occurred mostly at membrane potentials more positive than -70mV. 5. There was a clear correlation between activation speed of I-A(H) and the frequency of pulse-evoked oscillation. A 'hump'-type response was produced in about one-quarter of the oscillatory-type hair cells.