Referenced in: none

Automatically associated channels: Kir6.2

Title: The presynaptic function of mouse cochlear inner hair cells during development of hearing.

Authors: D Beutner, T Moser

Journal, date & volume: J. Neurosci., 2001 Jul 1 , 21, 4593-9

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/11425887

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.