The temporal characteristics of Ca2+ entry through L-type and T-type Ca2+ channels shape exocytosis efficiency in chick auditory hair cells during development.

1. J Neurophysiol. 2012 Dec;108(11):3116-23. doi: 10.1152/jn.00555.2012. Epub 2012
Sep 12.

The temporal characteristics of Ca2+ entry through L-type and T-type Ca2+
channels shape exocytosis efficiency in chick auditory hair cells during
development.

Levic S(1), Dulon D.

Author information:
(1)Equipe Neurophysiologie de la Synapse Auditive, Unité Mixte de Recherche,
Institut National de la Santé et de la Recherche Médicale U587 et Université
Bordeaux Segalen, Institut des Neurosciences de Bordeaux, Centre Hospitalier
Universitaire Pellegrin, Bordeaux, France.

During development, synaptic exocytosis by cochlear hair cells is first initiated
by patterned spontaneous Ca(2+) spikes and, at the onset of hearing, by
sound-driven graded depolarizing potentials. The molecular reorganization
occurring in the hair cell synaptic machinery during this developmental
transition still remains elusive. We characterized the changes in biophysical
properties of voltage-gated Ca(2+) currents and exocytosis in developing auditory
hair cells of a precocial animal, the domestic chick. We found that immature
chick hair cells (embryonic days 10-12) use two types of Ca(2+) currents to
control exocytosis: low-voltage-activating, rapidly inactivating (mibefradil
sensitive) T-type Ca(2+) currents and high-voltage-activating, noninactivating
(nifedipine sensitive) L-type currents. Exocytosis evoked by T-type Ca(2+)
current displayed a fast release component (RRP) but lacked the slow sustained
release component (SRP), suggesting an inefficient recruitment of distant
synaptic vesicles by this transient Ca(2+) current. With maturation, the
participation of L-type Ca(2+) currents to exocytosis largely increased, inducing
a highly Ca(2+) efficient recruitment of an RRP and an SRP component. Notably,
L-type-driven exocytosis in immature hair cells displayed higher Ca(2+)
efficiency when triggered by prerecorded native action potentials than by voltage
steps, whereas similar efficiency for both protocols was found in mature hair
cells. This difference likely reflects a tighter coupling between release sites
and Ca(2+) channels in mature hair cells. Overall, our results suggest that the
temporal characteristics of Ca(2+) entry through T-type and L-type Ca(2+)
channels greatly influence synaptic release by hair cells during cochlear
development.

DOI: 10.1152/jn.00555.2012
PMID: 22972963 [Indexed for MEDLINE]

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