Increase in efficiency and reduction in Ca2+ dependence of exocytosis during development of mouse inner hair cells

Johnson, Stuart L, Marcotti, Walter and Kros, Corné J (2005) Increase in efficiency and reduction in Ca2+ dependence of exocytosis during development of mouse inner hair cells. Journal of Physiology, 563 (1). pp. 177-191. ISSN 0022-3751

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Developmental changes in the coupling between Ca2+ entry and exocytosis were studied in mouse inner hair cells (IHCs) which, together with the afferent endings, form the primary synapse of the mammalian auditory system. Ca2+ currents (ICa) and changes in membrane capacitance (¿Cm) were recorded using whole-cell voltage clamp from cells maintained at body temperature, using physiological (1.3 mM) extracellular Ca2+. The magnitudes of both ICa and ¿Cm increased with maturation from embryonic stages until postnatal day 6 (P6). Subsequently, ICa gradually declined to a steady level of about -100 pA from P13 while the Ca2+-induced ¿Cm remained relatively constant, indicating a developmental increase in the Ca2+ efficiency of exocytosis. Although the size of ICa changed during development, its activation properties did not, suggesting the presence of a homogeneous population of Ca2+ channels in IHCs throughout development. The Ca2+ dependence of exocytosis changed with maturation from a fourth power relation in immature cells to an approximately linear relation in mature cells. This change applies to the release of both a readily releasable pool (RRP) and a slower secondary pool of vesicles, implying a common release mechanism for these two kinetically distinct pools that becomes modified during development. The increased Ca2+ efficiency and linear Ca2+ dependence of mature IHC exocytosis, especially over the physiological range of intracellular Ca2+, could improve the high-fidelity transmission of both brief and long-lasting stimulation. These properties make the mature cell ideally suited for fine intensity discrimination over a wide dynamic range.

Item Type: Article
Additional Information: All experiments done in the Kros lab, mostly by Kros¿s DPhil student Johnson with some contributions from Kros¿s postdoc Marcotti. Kros planned and oversaw the work and is corresponding author.
Schools and Departments: School of Life Sciences > Neuroscience
Depositing User: Corne Kros
Date Deposited: 06 Feb 2012 18:30
Last Modified: 23 Mar 2012 11:13
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