Spontaneous oscillation by hair bundles of the bullfrog's sacculus.
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 nonmammalian hair cells, we investigated the ability of hair bundles in the bullfrog's sacculus to produce oscillations that might underlie spontaneous otoacoustic emissions. When maintained in the normal ionic milieu of the ear, many bundles oscillated spontaneously through distances as great as 80 nm at frequencies of 5-50 Hz. Whole-cell recording disclosed that the positive phase of movement was associated with the opening of transduction channels. Gentamicin, which blocks transduction channels, reversibly arrested oscillation; drugs that affect the cAMP phosphorylation pathway and might influence the activity of myosin altered the rate of oscillation. Increasing the Ca 2+ concentration rendered oscillations faster and smaller until they were suppressed; lowering the Ca 2+ concentration moderately with chelators had the opposite effect. When a bundle was offset with a stimulus fiber, oscillations were transiently suppressed but gradually resumed. Loading a bundle by partial displacement clamping, which simulated the presence of the accessory structures to which a bundle is ordinarily attached, increased the frequency and diminished 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 Ca 2+-dependent relaxation of gating springs.
Martin
Pascal
P
Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, New York, New York 10021-6399, USA.
Bozovic
D
D
Choe
Y
Y
Hudspeth
A J
AJ
D000818:Animals; D001683:Biological Clocks / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000494:pharmacology; D002923:Cilia / Q000187:drug effects / Q000502:physiology*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives* / Q000494:pharmacology; D003931:Diacetyl / Q000031:analogs & derivatives* / Q000494:pharmacology; D015194:Diffusion Chambers, Culture; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005839:Gentamicins / Q000494:pharmacology; D006198:Hair Cells, Auditory / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D007478:Iontophoresis; D018715:Microscopy, Video; D008954:Models, Biological; D020409:Molecular Motor Proteins; D019319:Okadaic Acid / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010812:Physical Stimulation; D011892:Rana catesbeiana / Q000502:physiology*; D012444:Saccule and Utricle / Q000166:cytology*; D013314:Stress, Mechanical; D013873:Thionucleotides / Q000494:pharmacology; D014970:Xanthines / Q000494:pharmacology
D004791:Enzyme Inhibitors; D005839:Gentamicins; D020409:Molecular Motor Proteins; D013873:Thionucleotides; D014970:Xanthines; C004717:diacetylmonoxime; D005576:Colforsin; D019319:Okadaic Acid; C016957:adenosine-3',5'-cyclic phosphorothioate; D000242:Cyclic AMP; D003931:Diacetyl; D002118:Calcium