The Rockefeller University - Laboratory of Sensory Neuroscience

Hair Cells of the Inner Ear

Transfer characteristics
of the hair cell's afferent synapse

Coherent motion of stereocilia assures the
concerted gating of hair-cell transduction channels

The structural and functional differentiation of
hair cells in a lizard's basilar papilla suggests
an operational principle of amniote cochleas

Analysis and functional evaluation of the hair-cell
transcriptome

Three-dimensional architecture of hair-bundle
linkages revealed by electron-microscopic
tomography

A two-step mechanism underlies the planar
polarization of regenerating sensory hair cells

Specificity of afferent synapses onto
plane-polarized hair cells in the
posterior lateral line of the zebrafish

Tuesday, December 02, 2008

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Electrical stimulation of hair-bundle movement

Electrically evoked otoacoustic emission, a form of reverse transduction by the inner ear, consists of the emission of sounds by an ear stimulated with sinusoidal electrical current. This phenomenon is one manifestation of the active process by which an ear amplifies its mechanical inputs. By applying transepithelial electrical stimuli to the frog's sacculus, we have identified a potential single-cell correlate of this phenomenon, electrically evoked hair-bundle movement. Responses can 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 have allowed us to distinguish two mechanisms that mediate the electrical responses: myosin-based adaptation and Ca²⁺-dependent reclosure of transduction channels. These mechanisms also contribute to the active process that amplifies and tunes the mechanical responses of this receptor organ. Transient application of the channel blocker gentamicin demonstrates the crucial role of mechanoelectrical transduction channels in the rapid responses to electrical stimulation. A model for electrically driven bundle motion that incorporates the hair bundle's negative stiffness as well as its two mechanisms of motility captures the essential features of the measured responses.