Abstract
In the inner ear of birds, as in mammals, reptiles and amphibians, acetylcholine released from efferent neurons inhibits hair cells via activation of an apamin-sensitive, calcium-dependent potassium current. The particular potassium channel involved in avian hair cell inhibition is unknown. In this study, we cloned a small-conductance, calcium-sensitive potassium channel (gSK2) from a chicken cochlear library. Using RT-PCR, we demonstrated the presence of gSK2 mRNA in cochlear hair cells. Electrophysiological studies on transfected HEK293 cells showed that gSK2 channels have a conductance of approximately 16 pS and a half-maximal calcium activation concentration of 0.74+/-0.17 microM. The expressed channels were blocked by apamin (IC(50)=73.3+/-5.0 pM) and d-tubocurarine (IC(50)=7.6+/-1.0 microM), but were insensitive to charybdotoxin. These characteristics are consistent with those reported for acetylcholine-induced potassium currents of isolated chicken hair cells, suggesting that gSK2 is involved in efferent inhibition of chicken inner ear. These findings imply that the molecular mechanisms of inhibition are conserved in hair cells of all vertebrates.
Publication types
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Comparative Study
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Sequence
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Animals
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Animals, Newborn
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Apamin / pharmacology
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Blotting, Southern / methods
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Calcium / pharmacology
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Cell Line
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Chickens
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Cloning, Molecular / methods
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Cochlea / cytology*
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Dose-Response Relationship, Drug
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Electric Stimulation / methods
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Gene Library
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Hair Cells, Auditory / physiology*
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Humans
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Membrane Potentials / drug effects
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Membrane Potentials / physiology
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Membrane Potentials / radiation effects
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Mice
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Molecular Sequence Data
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Nicotinic Antagonists / pharmacology
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Patch-Clamp Techniques / methods
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Potassium Channels, Calcium-Activated / genetics*
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Potassium Channels, Calcium-Activated / metabolism
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RNA, Messenger / biosynthesis
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Rats
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Reverse Transcriptase Polymerase Chain Reaction / methods
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Small-Conductance Calcium-Activated Potassium Channels
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Transfection / methods
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Tubocurarine / pharmacology
Substances
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KCNN2 protein, human
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Kcnn2 protein, mouse
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Kcnn2 protein, rat
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Nicotinic Antagonists
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Potassium Channels, Calcium-Activated
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RNA, Messenger
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Small-Conductance Calcium-Activated Potassium Channels
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Apamin
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Calcium
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Tubocurarine