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

Wednesday, October 08, 2008




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Spontaneous oscillation by hair bundles

One prominent manifestation of mechanical activity in hair cells is spontaneous otoacoustic emission, the unprovoked emanation of sound by an internal ear. Because active hair-bundle motility probably constitutes the active process of non-mammalian hair cells, we have investigated the ability of hair bundles in the bullfrog's sacculus to produce oscillations that might underlie spontaneous otoacoustic emissions. When maintained in the ear's normal ionic milieu, many bundles oscillate spontaneously through distances as great as 80 nm at frequencies of 5-50 Hz. Whole-cell recording discloses that the positive phase of movement is associated with the opening of transduction channels. Gentamicin, which blocks transduction channels, reversibly arrests oscillation; drugs that affect the cAMP phosphorylation pathway or interfere with myosin's activity alter the rate of oscillation. Increasing the Ca²⁺ concentration renders oscillations faster and smaller until they are suppressed; lowering the Ca²⁺ concentration moderately with chelators has the opposite effect. When a bundle is offset with a stimulus fiber, oscillations are transiently suppressed but gradually resume. Loading a bundle by partial displacement clamping, which simulates the presence of the accessory structures to which a bundle is ordinarily attached, increases the frequency and diminishes the magnitude of oscillation. These observations accord with a model in which oscillations arise from the interplay of the hair bundle's negative stiffness with the activity of adaptation motors and with Ca²⁺ -dependent relaxation of gating springs.