title: TRPC-like conductance mediates restoration of intracellular Ca2+ in cochlear outer hair cells in the guinea pig and rat.
abstract: Ca2+ signalling is central to cochlear sensory hair cell physiology through its influence on sound transduction, membrane filter properties and neurotransmission. However, the mechanism for establishing Ca2+ homeostasis in these cells remains unresolved. Canonical transient receptor potential (TRPC) Ca2+ entry channels provide an important pathway for maintaining intracellular Ca2+ levels. TRPC3 subunit expression was detected in guinea pig and rat organ of Corti by RT-PCR, and localized to the sensory and neural poles of the inner and outer hair cells (OHCs) by confocal immunofluorescence imaging. A cation entry current with a TRPC-like phenotype was identified in guinea pig and rat OHCs by whole-cell voltage clamp. This slowly activating current was induced by the lowering of cytosolic Ca2+ levels ([Ca2+]i) following a period in nominally Ca2+-free solution. Activation was dependent upon the [Ca2+]o and was sustained until [Ca(2+)]i was restored. Ca2+ entry was confirmed by confocal fluorescence imaging, and rapidly recruited secondary charybdotoxin- and apamin-sensitive K(Ca) currents. Dual activation by the G protein-coupled receptor (GPCR)-phospholipase C-diacylglycerol (DAG) second messenger pathway was confirmed using the analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG). Ion substitution experiments showed that the putative TRPC Ca2+ entry current was selective for Na+ > K+ with a ratio of 1: 0.6. The Ca2+ entry current was inhibited by the TRPC channel blocker 2-aminoethyl diphenylborate (2APB) and the tyrosine kinase inhibitor, erbstatin analogue. We conclude that TRPC Ca2+ entry channels, most likely incorporating TRPC3 subunits, support cochlear hair cell Ca2+ homeostasis and GPCR signalling.
authors.affiliation: Department of Physiology, University of Auckland, Private Bag 92019, Auckland, New Zealand.
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: Raybould
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Jagger
authors.forename: Refik
authors.initials: R
authors.lastname: Kanjhan
authors.forename: Denise
authors.initials: D
authors.lastname: Greenwood
authors.forename: Peter
authors.initials: P
authors.lastname: Laslo
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Hoya
authors.forename: Christian
authors.initials: C
authors.lastname: Soeller
authors.forename: Mark B
authors.initials: MB
authors.lastname: Cannell
authors.forename: Gary D
authors.initials: GD
authors.lastname: Housley
mesh_terms: D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics*; D020013:Calcium Signaling / Q000502:physiology*; D004075:Diglycerides / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D015870:Gene Expression / Q000502:physiology; D006168:Guinea Pigs; D018072:Hair Cells, Auditory, Outer / Q000502:physiology*; D006706:Homeostasis / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D015290:Second Messenger Systems / Q000502:physiology; D050052:TRPC Cation Channels / Q000235:genetics* / Q000378:metabolism*
chemical_list: D004075:Diglycerides; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled; D050052:TRPC Cation Channels; C104603:TRPC3 cation channel; D002118:Calcium