Expression of the SK2 calcium-activated potassium channel is required for cholinergic function in mouse cochlear hair cells

Jee Hyun Kong, John P. Adelman, Paul Albert Fuchs

Research output: Contribution to journalArticle

Abstract

Efferent inhibition of cochlear hair cells is mediated by 'nicotinic' cholinergic receptors functionally coupled to calcium-activated, small conductance (SK2) potassium channels. We recorded from cochlear hair cells in SK2 knockout mice to evaluate further the role of this channel in efferent function. Since cholinergic inhibitory synapses can be found on inner or outer hair cells, depending on developmental age, both cell types were studied. To determine if SK channel activity was indeed eliminated, seconds-long voltage-gated calcium influx was used to activate slowly rising and falling calcium-dependent potassium currents. These were identified as SK currents by their time course, calcium dependence and sensitivity to block by apamin in wild-type IHCs. IHCs from knockout mice had no SK current by these same criteria. Thus, the SK2 gene is solely responsible for encoding the SK channels of inner hair cells. Other aspects of hair cell excitability remained relatively unaffected. Unexpectedly, cholinergic synaptic currents were entirely absent from both inner and outer SK2-knockout hair cells. Further, direct application of ACh caused no change in membrane current, implying absent or otherwise dysfunctional ACh receptors. Immunohistology of whole-mounts using the antibody to the synaptic vesicle protein 2 (SV2) revealed a pronounced reduction of efferent innervation to outer hair cells (OHCs) in the knockout cochleas. Quantitative RT-PCR analysis, however, showed no change in the mRNA levels of α9 and α10 nicotinic ACh receptor (nAChR) genes. Thus, some aspect of translation or subsequent protein processing leads to non-functional or absent ACh receptors. These results indicate that SK2 channels are required both for expression of functional nAChRs, and for establishment and/or maintenance of efferent terminals in the cochlea.

Original languageEnglish (US)
Pages (from-to)5471-5485
Number of pages15
JournalJournal of Physiology
Volume586
Issue number22
DOIs
StatePublished - Nov 15 2008

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Auditory Hair Cells
Calcium-Activated Potassium Channels
Cholinergic Receptors
Outer Auditory Hair Cells
Inner Auditory Hair Cells
Cholinergic Agents
Cochlea
Nicotinic Receptors
Calcium
Knockout Mice
Small-Conductance Calcium-Activated Potassium Channels
Apamin
Synaptic Vesicles
Synapses
Genes
Potassium
Proteins
Maintenance
Polymerase Chain Reaction
Messenger RNA

ASJC Scopus subject areas

  • Physiology

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Expression of the SK2 calcium-activated potassium channel is required for cholinergic function in mouse cochlear hair cells. / Kong, Jee Hyun; Adelman, John P.; Fuchs, Paul Albert.

In: Journal of Physiology, Vol. 586, No. 22, 15.11.2008, p. 5471-5485.

Research output: Contribution to journalArticle

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