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Acetylcholine, outer hair cell electromotility, and the cochlear amplifier
1Auditory Physiology Laboratory (The Hugh Knowles Center), Department of Neurobiology, Institute for Neuroscience, Northwestern University, Evanston, Illinois 60208, USA.
Summary
Acetylcholine (ACh) increases outer hair cell (OHC) motility and compliance by affecting intracellular calcium stores. This finding suggests a novel mechanism for efferent control in the cochlea.
Area of Science:
- Neuroscience
- Auditory Physiology
- Cellular Mechanics
Background:
- The cochlea's efferent innervation primarily targets outer hair cells (OHCs).
- Acetylcholine (ACh) is the main neurotransmitter mediating efferent effects on OHCs.
- OHC electromotility, a somatic shape change, is crucial for auditory feedback.
Purpose of the Study:
- To investigate the effects of ACh on OHC electromotile responses.
- To elucidate the underlying mechanism of ACh action in OHCs.
Main Methods:
- Studied isolated OHCs to analyze electromotile responses.
- Measured axial electromotile amplitude and cell compliance.
- Correlated mechanical responses with membrane potential and intracellular calcium changes.
Main Results:
- ACh increased axial electromotile amplitude and OHC compliance.
- These mechanical changes occurred with a latency distinct from immediate electrical responses.
- The observed effects were contemporaneous with calcium release from intracellular stores.
Conclusions:
- Increased axial compliance likely explains the enhanced OHC motility induced by ACh.
- The findings suggest a slow efferent mechanism involving intracellular calcium.
- This challenges previous assumptions about in vivo efferent cochlear control.