TRPC-like conductance mediates restoration of intracellular Ca2+ in cochlear outer hair cells in the guinea pig and rat.
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.
Raybould
Nicholas P
NP
Department of Physiology, University of Auckland, Private Bag 92019, Auckland, New Zealand.
Jagger
Daniel J
DJ
Kanjhan
Refik
R
Greenwood
Denise
D
Laslo
Peter
P
Hoya
Noriyuki
N
Soeller
Christian
C
Cannell
Mark B
MB
Housley
Gary D
GD
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*
D004075:Diglycerides; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled; D050052:TRPC Cation Channels; C104603:TRPC3 cation channel; D002118:Calcium