Direct Measurement of the Action of Acetylcholine on Isolated Outer Hair Cells of the Guinea Pig Cochlea

Acetylcholine has long been thought to be the neurotransmitter of the cochlear efferent system in mammals although the evidence is largely indirect. By using whole-cell recordings from isolated outer hair cells, we show that acetylcholine activates a large rapidly desensitizing outward potassium cur...

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Bibliographic Details
Published in:Proceedings of the Royal Society. B, Biological sciences Biological sciences, 1991-05, Vol.244 (1310), p.161-167
Main Authors: Housley, G. D., Ashmore, Jonathan Felix
Format: Article
Language:English
Subjects:
Acetylcholine - pharmacology
Animals
Calcium
Cholinergic receptors
Cochlea
Electrophysiology
Guinea Pigs
Hair cells
Hair Cells, Auditory - drug effects
Hair Cells, Auditory - physiology
In Vitro Techniques
Membrane potential
Neurons
Outer hair cells
Pipettes
Potassium
Potassium - metabolism
Receptors
Receptors, Cholinergic - drug effects
Receptors, Cholinergic - physiology
Second Messenger Systems - drug effects
Second Messenger Systems - physiology
Synaptic Transmission - drug effects
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Summary:Acetylcholine has long been thought to be the neurotransmitter of the cochlear efferent system in mammals although the evidence is largely indirect. By using whole-cell recordings from isolated outer hair cells, we show that acetylcholine activates a large rapidly desensitizing outward potassium current. This corresponds to hyperpolarization of the membrane potential from rest. The half maximal dose for acetylcholine was 13.5 u.M with a cooperativity of 2. The response was not due to a conventional muscarinic action of acetylcholine for it was not blocked by 0.1 u.M atropine and muscarinic antagonists but it could be blocked by 0.1 uM curare, suggesting that it shared many properties of a nicotinic receptor. It was, however, inhibited by 10 uM strychnine. The potassium current activated by acetylcholine required external calcium and was characterized by a significant delay at room temperature. This points to the involvement of a second messenger system, possibly calcium itself.
ISSN:0962-8452
1471-2954
DOI:10.1098/rspb.1991.0065