title: HCN channels expressed in the inner ear are necessary for normal balance function.
abstract: HCN1-4 subunits form Na+/K+-permeable ion channels that are activated by hyperpolarization and carry the current known as I(h). I(h) has been characterized in vestibular hair cells of the inner ear, but its molecular correlates and functional contributions have not been elucidated. We examined Hcn mRNA expression and immunolocalization of HCN protein in the mouse utricle, a mechanosensitive organ that contributes to the sense of balance. We found that HCN1 is the most highly expressed subunit, localized to the basolateral membranes of type I and type II hair cells. We characterized I(h) using the whole-cell, voltage-clamp technique and found the current expressed in 84% of the cells with a mean maximum conductance of 4.4 nS. I(h) was inhibited by ZD7288, cilobradine, and by adenoviral expression of a dominant-negative form of HCN2. To determine which HCN subunits carried I(h), we examined hair cells from mice deficient in Hcn1, 2, or both. I(h) was completely abolished in hair cells of Hcn1⁻/⁻ mice and Hcn1/2⁻/⁻ mice but was similar to wild-type in Hcn2⁻/⁻ mice. To examine the functional contributions of I(h), we recorded hair cell membrane responses to small hyperpolarizing current steps and found that activation of I(h) evoked a 5-10 mV sag depolarization and a subsequent 15-20 mV rebound upon termination. The sag and rebound were nearly abolished in Hcn1-deficient hair cells. We also found that Hcn1-deficient mice had deficits in vestibular-evoked potentials and balance assays. We conclude that HCN1 contributes to vestibular hair cell function and the sense of balance.
authors.affiliation: Department of Neuroscience and Department of Otolaryngology, University of Virginia School of Medicine, Charlottesville, Virginia 22908, USA.
authors.forename: Geoffrey C
authors.initials: GC
authors.lastname: Horwitz
authors.forename: Jessica R
authors.initials: JR
authors.lastname: Risner-Janiczek
authors.forename: Sherri M
authors.initials: SM
authors.lastname: Jones
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Holt
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001552:Benzazepines / Q000494:pharmacology; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D007758:Ear, Inner / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D005260:Female; D051858:Forkhead Transcription Factors / Q000235:genetics; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D009038:Motion; D009419:Nerve Tissue Proteins / Q000235:genetics; D016900:Neurofilament Proteins / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010880:Piperidines / Q000494:pharmacology; D004856:Postural Balance / Q000235:genetics*; D015221:Potassium Channels / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D045442:Rotarod Performance Test; D012444:Saccule and Utricle / Q000166:cytology / Q000378:metabolism*; D058585:Vestibular Evoked Myogenic Potentials / Q000235:genetics / Q000502:physiology
chemical_list: D001552:Benzazepines; D054815:Cyclic Nucleotide-Gated Cation Channels; D051858:Forkhead Transcription Factors; C489565:Foxg1 protein, mouse; C578666:Hcn1 protein, mouse; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D009419:Nerve Tissue Proteins; D016900:Neurofilament Proteins; D010880:Piperidines; D015221:Potassium Channels; D011743:Pyrimidines; D012333:RNA, Messenger; C051774:neurofilament protein H; C082246:ICI D2788; D015124:8-Bromo Cyclic Adenosine Monophosphate; C490484:cilobradine
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