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 (IA(H)) was found to be a major outward current underlying the oscillatory response. 4. IA(H) was activated with a time constant of 0.4‐10 ms and was inactivated slowly with a time constant of 0.6‐2 s. IA(H) activation and inactivation occurred mostly at membrane potentials more positive than ‐70 mV. 5. There was a clear correlation between activation speed of IA(H) and the frequency of pulse‐evoked oscillation. A ‘hump’‐type response was produced in about one‐quarter of the oscillatory‐type hair cells.