title: The function and molecular identity of inward rectifier channels in vestibular hair cells of the mouse inner ear.
abstract: Inner ear hair cells respond to mechanical stimuli with graded receptor potentials. These graded responses are modulated by a host of voltage-dependent currents that flow across the basolateral membrane. Here, we examine the molecular identity and the function of a class of voltage-dependent ion channels that carries the potassium-selective inward rectifier current known as I(K1). I(K1) has been identified in vestibular hair cells of various species, but its molecular composition and functional contributions remain obscure. We used quantitative RT-PCR to show that the inward rectifier gene, Kir2.1, is highly expressed in mouse utricle between embryonic day 15 and adulthood. We confirmed Kir2.1 protein expression in hair cells by immunolocalization. To examine the molecular composition of I(K1), we recorded voltage-dependent currents from type II hair cells in response to 50-ms steps from -124 to -54 in 10-mV increments. Wild-type cells had rapidly activating inward currents with reversal potentials close to the K(+) equilibrium potential and a whole-cell conductance of 4.8 ± 1.5 nS (n = 46). In utricle hair cells from Kir2.1-deficient (Kir2.1(-/-)) mice, I(K1) was absent at all stages examined. To identify the functional contribution of Kir2.1, we recorded membrane responses in current-clamp mode. Hair cells from Kir2.1(-/-) mice had significantly (P < 0.001) more depolarized resting potentials and larger, slower membrane responses than those of wild-type cells. These data suggest that Kir2.1 is required for I(K1) in type II utricle hair cells and contributes to hyperpolarized resting potentials and fast, small amplitude receptor potentials in response to current inputs, such as those evoked by hair bundle deflections.
authors.affiliation: Department of Neuroscience, University of Virginia School of Medicine, Charlottesville, Virginia, USA.
authors.forename: Michaela E
authors.initials: ME
authors.lastname: Levin
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Holt
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D000831:Animals, Newborn; D017609:Barium Compounds / Q000494:pharmacology; D001703:Biophysics; D002712:Chlorides / Q000494:pharmacology; D007758:Ear, Inner / Q000166:cytology*; D004558:Electric Stimulation; D004622:Embryo, Mammalian; D005822:Genetic Vectors / Q000502:physiology; D049452:Green Fluorescent Proteins / Q000235:genetics; D057809:HEK293 Cells; D018069:Hair Cells, Vestibular / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects / Q000235:genetics*; D008564:Membrane Potentials / Q000235:genetics / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D018408:Patch-Clamp Techniques; D017354:Point Mutation / Q000235:genetics; D024661:Potassium Channels, Inwardly Rectifying / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D014162:Transfection / Q000379:methods
chemical_list: D017609:Barium Compounds; D002712:Chlorides; C489461:Kir2.1 channel; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger; C024986:barium chloride; D049452:Green Fluorescent Proteins