title: The presynaptic function of mouse cochlear inner hair cells during development of hearing.
abstract: Before mice start to hear at approximately postnatal day 10, their cochlear inner hair cells (IHCs) spontaneously generate Ca(2+) action potentials. Therefore, immature IHCs could stimulate the auditory pathway, provided that they were already competent for transmitter release. Here, we combined patch-clamp capacitance measurements and fluorimetric [Ca(2+)](i) recordings to study the presynaptic function of IHCs during cochlear maturation. Ca(2+)-dependent exocytosis and subsequent endocytic membrane retrieval were already observed near the date of birth. Ca(2+) action potentials triggered exocytosis in immature IHCs, which probably activates the auditory pathway before it becomes responsive to sound. IHCs underwent profound changes in Ca(2+)-channel expression and secretion during their postnatal development. Ca(2+)-channel expression increased toward the end of the first week, providing for large secretory responses during this period and thereafter declined to reach mature levels. The efficacy whereby Ca(2+) influx triggers exocytosis increased toward maturation, such that vesicle fusion caused by a given Ca(2+) current occurred faster in mature IHCs. The observed changes in Ca(2+)-channel expression and synaptic efficacy probably reflected the ongoing synaptogenesis in IHCs that had been described previously in morphological studies.
authors: Department of Membrane Biophysics, Max Planck Institute for Biophysical Chemistry, Am Fassberg, 37077 Göttingen, Germany.
authors: D
authors: D
authors: Beutner
authors: T
authors: T
authors: Moser
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000375:Aging / Q000502:physiology; D000818:Animals; D001306:Auditory Pathways / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D003051:Cochlea / Q000166:cytology / Q000254:growth & development* / Q000294:innervation*; D004533:Egtazic Acid / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology; D006199:Hair Cells, Auditory, Inner / Q000187:drug effects / Q000502:physiology*; D006309:Hearing / Q000502:physiology*; D066298:In Vitro Techniques; D051379:Mice; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000378:metabolism*
chemical_list: D015220:Calcium Channels; D002614:Chelating Agents; D004533:Egtazic Acid; D002118:Calcium