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Fast adaptation of mechanoelectrical transducer channels in mammalian cochlear hair cells

Abstract

Outer hair cells are centrally involved in the amplification and frequency tuning of the mammalian cochlea, but evidence about their transducing properties in animals with fully developed hearing is lacking. Here we describe measurements of mechanoelectrical transducer currents in outer hair cells of rats between postnatal days 5 and 18, before and after the onset of hearing. Deflection of hair bundles using a new rapid piezoelectric stimulator evoked transducer currents with ultra-fast activation and adaptation kinetics. Fast adaptation resembled the same process in turtle hair cells, where it is regulated by changes in stereociliary calcium. It is argued that sub-millisecond transducer adaptation can operate in outer hair cells under the ionic, driving force and temperature conditions that prevail in the intact mammalian cochlea.

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Figure 1: Ca2+ modulation of mechanotransducer currents in outer hair cells.
Figure 2: Adaptation rate depends on the size of the transducer current.
Figure 3: Adaptation rate increases with holding potential.
Figure 4: Properties of mechanotransduction during cochlear maturation.
Figure 5: Outer hair cell voltage-dependent currents change with maturation.

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Acknowledgements

This work was supported by grant RO1 DC 01362 to R.F. from the National Institutes on Deafness and other Communicative Disorders (NIH) and travel grants to M.G.E. and H.J.K. from the Wellcome Trust.

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Correspondence to Robert Fettiplace.

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Supplementary information

Supplementary Fig. 1. (a)

Low-power view of isolated cochlear coil showing arrangement of recording pipette and stimulating probe.The preparation was secured by four ties one of which is visible near the top of the image.The recording pipette was inserted along the longitudinal axis of the cochlea. (b) Method for stimulating stereociliary bundle.The bundle was deflected by axial motion of a fire-polished glass probe driven by a piezoelectric stack actuator. The apical surface of the hair cell on the right shows that the tip of the glass probe fit into the 'V' of of the outer hair cell bundle. Diameter of probe tip was 3 μm. (JPG 47 kb)

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Kennedy, H., Evans, M., Crawford, A. et al. Fast adaptation of mechanoelectrical transducer channels in mammalian cochlear hair cells. Nat Neurosci 6, 832–836 (2003). https://doi.org/10.1038/nn1089

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