Persistence of Cav1.3 Ca2+ Channels in Mature Outer Hair Cells Supports Outer Hair Cell Afferent Signaling

• DOI: 10.1523/jneurosci.5364-06.2007
• Publication Date: 2007-06-14T05:09:30Z
• Authors: M. Knirsch; N. Brandt; C. Braig; S. Kuhn; B. Hirt; S. Munkner; M. Knipper; J. Engel
• Keywords: Ribbon synapse

Outer hair cells (OHCs) are innervated by type II afferent fibers of as yet unknown function. It is still a matter debate whether OHCs perform exocytosis. If so, they would require presynaptic Ca²⁺ channels at their basal poles where the make contacts. Here we show that L-type channel currents (charge carrier, 10 mm Ba²⁺) present in neonatal [postnatal day 1 (P1) to P7] decreased from ∼170 ∼50 pA approximately onset hearing. Ba²⁺ could hardly be measured mature mouse because high fragility, whereas rat, average current amplitude apical was 58 ± 9 (<i>n</i> = 20, P19–P30) compared with inner (IHCs) 181 50 24, P17–P30). Properties resembled those OHCs. One exception voltage dependence activation shifted between birth and P12 +9 mV toward positive voltages OHCs, it remained constant IHCs. Ca_v1.3-specific mRNA detected using cell-specific reverse transcription (RT)-PCR <i>in situ</i> hybridization. Ca_v1.3 protein stained exclusively base colocalization ribbon synapse CtBP2 (C-terminal binding 2)/RIBEYE. When sizes were normalized estimated number or ribbons, comparable values for IHCs obtained, finding together CtBP2/RIBEYE strongly suggests role exocytosis