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The Journal of Neuroscience, January 1, 2002, 22(1):44-52
Mechanisms of Active Hair Bundle Motion in Auditory Hair
Cells
A. J.
Ricci1,
A. C.
Crawford2, and
R.
Fettiplace3
1 Neuroscience Center, Louisiana State University
Health Sciences Center, New Orleans, Louisiana 70112, 2 Department of Physiology, University of Cambridge,
Cambridge CB2 3EG, United Kingdom, and 3 Department of
Physiology, University of Wisconsin Medical School, Madison, Wisconsin
53706
Sound stimuli vibrate the hair bundles on auditory hair cells, but
the resulting motion attributable to the mechanical stimulus may
be modified by forces intrinsic to the bundle, which drive it actively.
One category of active hair bundle motion has properties similar to
fast adaptation of the mechanotransducer channels and is explicable if
gating of the channels contributes significantly to the mechanics of
the hair bundle. To explore this mechanism, we measured hair bundle
compliance in turtle auditory hair cells under different conditions
that alter the activation range of the channel.
Force-displacement relationships were nonlinear, possessing a maximum
slope compliance when approximately one-half of the transducer channels
were open. When the external calcium concentration was reduced from 2.8 to 0.25 mM, the position of maximum compliance was shifted
negative, reflecting a comparable shift in the transducer channel
activation curve. Assuming that the nonlinearity represents the
compliance attributable to channel gating, a single-channel gating
force of 0.25 pN was calculated. By comparing bundle displacements with
depolarization with and without an attached flexible fiber, the force
contributed by each channel was independently estimated as 0.47 pN.
These results are consistent with fast active bundle movements
resulting from changes in mechanotransducer channel gating. However,
several observations revealed additional components of hair bundle
motion, with slower kinetics and opposite polarity to the fast movement but also linked to transducer adaptation. This finding argues for
multiple mechanisms for controlling hair bundle position in auditory
hair cells.
Key words:
adaptation; cochlear amplifier; hair cell; hair bundle movements; mechanosensitive channel; stereociliary
bundle
Copyright © 2002 Society for Neuroscience 0270-6474/02/22144-09$05.00/0
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