Tonotopic map of potassium currents in chick auditory hair cells using an intact basilar papilla

The avian basilar papilla is tonotopically organized such that hair cells a long the sensory epithelium respond best to acoustic stimulation at differi ng frequencies. This specificity arises due to the mechanics of the cochlea itself and intrinsic electrical properties of the hair cells. Tall hair ce lls show membrane voltage oscillations in response to step current injectio n that may allow cells to act as electrical resonators, boosting the respon se at the resonant frequency. These oscillations and the underlying current s have been studied in enzymatically isolated cells. This study uses a whol e chick (Gallus domesticus) basilar papilla preparation where the entire ep ithelium and its afferent connections are intact. With this preparation, a map of changes in potassium currents of tail hair cells was produced. All c ells recorded from expressed two K+ currents, a calcium-activated K+ curren t, I-K(Ca), and a voltage-activated K+ current, I-K. Also, apical cells exp ressed an inward rectifier K+ current, IIR The amplitude of total outward c urrent increases in a gradient along the tonotopic axis. pharmacological bl ockers were used to separate the outward K+ currents. These experiments sho wed that both currents individually increase in magnitude along a gradient from apex to base. Finally, measurements of oscillation frequency in respon se to current steps suggest a discontinuous change in the electrical resona nces at about 33% from the apex. This study demonstrates a new preparation to study the electrical properties of hair cells in more detail along the t onotopic axis of the chick basilar papilla. (C) 2001 Elsevier Science B.V. All rights reserved.