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Article Dans Une Revue Journal of Neuroscience Année : 2008

Calcium- and Otoferlin-Dependent Exocytosis by Immature Outer Hair Cells

Résumé

Immature cochlear outer hair cells (OHCs) make transient synaptic contacts (ribbon synapses) with type I afferent nerve fibers, but direct evidence of synaptic vesicle exocytosis is still missing. We thus investigated calcium-dependent exocytosis in murine OHCs at postnatal day 2 (P2)–P3, a developmental stage when calcium current maximum amplitude was the highest. By using time-resolved patch-clamp capacitance measurements, we show that voltage step activation of L-type calcium channels triggers fast membrane capacitance increase. Capacitance increase displayed two kinetic components, which are likely to reflect two functionally distinct pools of synaptic vesicles, a readily releasable pool (RRP; τ = 79 ms) and a slowly releasable pool (τ = 870 ms). The RRP size and maximal release rate were estimated at ∼1200 vesicles and ∼15,000 vesicles/s, respectively. In addition, we found a linear relationship between capacitance increase and calcium influx, like in mature inner hair cells (IHCs). These results give strong support to the existence of efficient calcium-dependent neurotransmitter release in immature OHCs. Moreover, we show that immature OHCs, just like immature IHCs, are able to produce regenerative calcium-dependent action potentials that could trigger synaptic exocytosis in vivo . Finally, the evoked membrane capacitance increases were abolished in P2–P3 OHCs from mutant Otof −/− mice defective for otoferlin, despite normal calcium currents. We conclude that otoferlin, the putative major calcium sensor at IHC ribbon synapses, is essential to synaptic exocytosis in immature OHCs too.
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hal-04159607 , version 1 (12-07-2023)

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Paternité

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Maryline Beurg, Saaid Safieddine, Isabelle Roux, Yohan Bouleau, Christine Petit, et al.. Calcium- and Otoferlin-Dependent Exocytosis by Immature Outer Hair Cells. Journal of Neuroscience, 2008, 28 (8), pp.1798-1803. ⟨10.1523/JNEUROSCI.4653-07.2008⟩. ⟨hal-04159607⟩
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