Isolation and possible role of fast and slow potassium current components in hair cells dissociated from frog crista ampullaris.

Potassium-current inactivation and recovery kinetics are pivotal in sustaining dynamic processing of time-varying sensory signals in hair cells. We report a detailed analysis of K(+)-currents in isolated hair cells from the frog crista ampullaris. The single components were dissected using a novel procedure based on their differential kinetic properties: The fast IA component exhibited two processes of inactivation removal; the persistent I (KD) component (I (KV) + I (KCa)), unexpectedly displayed partial inactivation, removed by negative potentials with particularly slow, delayed kinetics. The physiological relevance of these observations was investigated by imposing sinusoidal membrane potential changes to mimic receptor response to hair bundle deflection. The excitatory phase elicited extra-currents (hysteresis) only if the off phase went sufficiently negative to remove IA inactivation. Native, resting hair cells are depolarised by receptor current; thus, voltage continuously modulates I(KD), whereas IA only transiently ensues when the receptor current vanishes (zero-current potential approximately -70 mV) and polarisation removes IA inactivation.