Voltage-gated potassium current and resonance in the toadfish saccular hair cell

Abstract

Resonance of the membrane potential in response to a perturbing current has been demonstrated in sensory hair cells of many acousticolateralis systems and modelled as the result of the interaction of passive membrane properties and the magnitude and kinetics of activation and deactivation of an outward calcium-activated potassium current (I KCa) and an inward calcium current (I Ca). However, the majority of the hair cells of the toadfish saccule have, in addition to I KCa, a voltage-gated potassium current (I K) active in the same membrane potential range as I KCa but with considerably slower activation and deactivation kinetics. Additionally, some of these cells have an A current I A. In the present work, the resonance of cells with these three outward potassium currents were compared with those from cells containing only I KCa. Hair cells with only I KCa produced a high-quality factor ( Q) resonance with symmetrical ringing at current onset and termination. In many cells having the I K, resonance could beevoked as a high Q ringing only at the onset of the current pulse. The resonance at command onset was dependent on the presence of I KCa and could be converted into a spike by blocking the I KCa with TEA > Some hair cells with I KCa and I K produced spikes rather than resonance at all holding potentials testes. This spiking was seen in cells with low levels of I KCa or slowly activating I KCa and with cells with I A. The presence of cells with such different response modes implies a difference between hair cells in their role in sensory coding.