Hair-bundle movements elicited by transepithelial electrical stimulation of hair cells in the sacculus of the bullfrog

Electrically evoked otoacoustic emission is a manifestation of reverse transduction by the inner ear. We present evidence for a single-cell correlate of this phenomenon, hair-bundle movement driven by transepithelial electrical stimulation of the frog's sacculus. Responses could be observed at stimulus frequencies up to 1 kHz, an order of magnitude higher than the organ's natural range of sensitivity to acceleration or sound. Measurements at high-stimulus frequencies and pharmacological treatments allow us to distinguish two mechanisms that mediate the electrical responses: myosin-based adaptation and Ca2+-dependent reclosure of transduction channels. These mechanisms also participate in the active process that amplifies and tunes the mechanical responses of this receptor organ. Transient application of the channel blocker gentamicin demonstrated the crucial role of mechanoelectrical transduction channels in the rapid responses to electrical stimulation. A model for electrically driven bundle motion that incorporates the negative stiffness of the hair bundle as well as its two mechanisms of motility captures the essential features of the measured responses.