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An intrinsic frequency limit to the cochlear amplifier

J E Gale1, J F Ashmore

  • 1Department of Physiology, School of Medical Sciences, Bristol, UK.

Nature
|September 4, 1997
PubMed
Summary

The mammalian cochlear amplifier, crucial for hearing, uses outer hair cells. This study reveals the motor protein limiting hearing range operates near 25 kHz, suggesting it’s a transporter, not an ion channel.

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Area of Science:

  • Auditory Neuroscience
  • Mammalian Physiology
  • Molecular Biophysics

Background:

  • Mammalian hearing relies on the cochlear amplifier, a feedback mechanism in the inner ear.
  • Outer hair cells (OHCs) are key components, transducing sound-induced motion and generating forces to counteract viscous damping.
  • OHCs enhance auditory sensitivity and frequency selectivity by altering cochlear mechanics.

Purpose of the Study:

  • To identify the molecular basis of the cochlear amplifier mechanism.
  • To determine the operational frequency limit of the voltage-sensitive motor protein in OHCs.
  • To infer the protein's molecular identity based on its function.

Main Methods:

  • Utilized voltage clamp techniques on isolated OHC membrane patches.
  • Measured both charge movement and mechanical motion associated with the motor protein.
  • Analyzed the frequency response of the motor protein's activity.

Main Results:

  • The motor protein's limiting operating frequency was found to be near 25 kHz.
  • Fast charge movement was observed, indicative of charge displacement within the molecule.
  • This frequency limit suggests an upper bound for mammalian hearing via this mechanism.

Conclusions:

  • The identified motor protein's operational frequency near 25 kHz sets a limit for mammalian hearing.
  • The rapid charge movement suggests the protein functions as a transporter rather than a modified ion channel.
  • Further research into this transporter protein is warranted to fully elucidate the cochlear amplifier.

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