title: Persistence of Ca(v)1.3 Ca2+ channels in mature outer hair cells supports outer hair cell afferent signaling.
abstract: Outer hair cells (OHCs) are innervated by type II afferent fibers of as yet unknown function. It is still a matter of debate whether OHCs perform exocytosis. If so, they would require presynaptic Ca2+ channels at their basal poles where the type II fibers make contacts. Here we show that L-type Ca2+ channel currents (charge carrier, 10 mM Ba2+) present in neonatal OHCs [postnatal day 1 (P1) to P7] decreased from approximately 170 to approximately 50 pA at approximately the onset of hearing. Ba2+ currents could hardly be measured in mature mouse OHCs because of their high fragility, whereas in the rat, the average Ba2+ current amplitude of apical OHCs was 58 +/- 9 pA (n = 20, P19-P30) compared with that of the inner hair cells (IHCs) of 181 +/- 50 pA (n = 24, P17-P30). Properties of Ba2+ currents of mature OHCs resembled those of neonatal OHCs. One exception was the voltage dependence of activation that shifted between birth and P12 by +9 mV toward positive voltages in OHCs, whereas it remained constant in the IHCs. Ca(v)1.3-specific mRNA was detected in mature OHCs using cell-specific reverse transcription (RT)-PCR and in situ hybridization. Ca(v)1.3 protein was stained exclusively at the base of mature OHCs, in colocalization with the ribbon synapse protein CtBP2 (C-terminal binding protein 2)/RIBEYE. When current sizes were normalized to the estimated number of afferent fibers or presynaptic ribbons, comparable values for IHCs and OHCs were obtained, a finding that together with the colocalization of Ca(v)1.3 and CtBP2/RIBEYE protein strongly suggests a role for Ca(v)1.3 channels in exocytosis of mature OHCs.
authors.affiliation: Institute of Physiology II, University of Tübingen, D-72076 Tübingen, Germany.
authors.forename: Martina
authors.initials: M
authors.lastname: Knirsch
authors.forename: Niels
authors.initials: N
authors.lastname: Brandt
authors.forename: Claudia
authors.initials: C
authors.lastname: Braig
authors.forename: Stephanie
authors.initials: S
authors.lastname: Kuhn
authors.forename: Bernhard
authors.initials: B
authors.lastname: Hirt
authors.forename: Stefan
authors.initials: S
authors.lastname: Münkner
authors.forename: Marlies
authors.initials: M
authors.lastname: Knipper
authors.forename: Jutta
authors.initials: J
authors.lastname: Engel
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000367:Age Factors; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D001464:Barium / Q000494:pharmacology; D002120:Calcium Channel Agonists / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000235:genetics / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D006199:Hair Cells, Auditory, Inner / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D018072:Hair Cells, Auditory, Outer / Q000254:growth & development / Q000378:metabolism*; D017403:In Situ Hybridization / Q000379:methods; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D015398:Signal Transduction / Q000502:physiology*
chemical_list: C472073:CACNA1D protein, human; D002120:Calcium Channel Agonists; D020746:Calcium Channels, L-Type; D002712:Chlorides; D001464:Barium; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester