title: Developmental changes in two voltage-dependent sodium currents in utricular hair cells.
abstract: Two kinds of sodium current (I(Na)) have been separately reported in hair cells of the immature rodent utricle, a vestibular organ. We show that rat utricular hair cells express one or the other current depending on age (between postnatal days 0 and 22, P0-P22), hair cell type (I, II, or immature), and epithelial zone (striola vs. extrastriola). The properties of these two currents, or a mix, can account for descriptions of I(Na) in hair cells from other reports. The patterns of Na channel expression during development suggest a role in establishing the distinct synapses of vestibular hair cells of different type and epithelial zone. All type I hair cells expressed I(Na,1), a TTX-insensitive current with a very negative voltage range of inactivation (midpoint: -94 mV). I(Na,2) was TTX sensitive and had less negative voltage ranges of activation and inactivation (inactivation midpoint: -72 mV). I(Na,1) dominated in the striola at all ages, but current density fell by two-thirds after the first postnatal week. I(Na,2) was expressed by 60% of hair cells in the extrastriola in the first week, then disappeared. In the third week, all type I cells and about half of type II cells had I(Na,1); the remaining cells lacked sodium current. I(Na,1) is probably carried by Na(V)1.5 subunits based on biophysical and pharmacological properties, mRNA expression, and immunoreactivity. Na(V)1.5 was also localized to calyx endings on type I hair cells. Several TTX-sensitive subunits are candidates for I(Na,2).
authors.affiliation: Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Julian R A
authors.initials: JR
authors.lastname: Wooltorton
authors.forename: Sophie
authors.initials: S
authors.lastname: Gaboyard
authors.forename: Karen M
authors.initials: KM
authors.lastname: Hurley
authors.forename: Steven D
authors.initials: SD
authors.lastname: Price
authors.forename: Jasmine L
authors.initials: JL
authors.lastname: Garcia
authors.forename: Meng
authors.initials: M
authors.lastname: Zhong
authors.forename: Anna
authors.initials: A
authors.lastname: Lysakowski
authors.forename: Ruth Anne
authors.initials: RA
authors.lastname: Eatock
mesh_terms: D000375:Aging / Q000378:metabolism / Q000502:physiology; D000465:Algorithms; D000818:Animals; D002469:Cell Separation; D002586:Cesium / Q000502:physiology; D017931:DNA Primers; D004847:Epithelial Cells / Q000187:drug effects; D005071:Evoked Potentials / Q000502:physiology; D006199:Hair Cells, Auditory, Inner / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology*; D006207:Half-Life; D007150:Immunohistochemistry; D062554:NAV1.5 Voltage-Gated Sodium Channel; D009431:Neural Conduction / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D020318:Rats, Long-Evans; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012444:Saccule and Utricle / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology*; D015222:Sodium Channels / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D017931:DNA Primers; D062554:NAV1.5 Voltage-Gated Sodium Channel; C568322:Scn5a protein, rat; D015222:Sodium Channels; D002586:Cesium; D013779:Tetrodotoxin