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Voltage‐Gated Na + Channel Activation Induces Both Action Potentials in Utricular Hair Cells and Brain‐Derived Neurotrophic Factor Release in the Rat Utricle During a Restricted Period of Development
Author(s) -
Chabbert Christian,
Mechaly Ilana,
Sieso Victor,
Giraud Pierre,
Brugeaud Aurore,
Lehouelleur Jacques,
Couraud François,
Valmier Jean,
Sans Alain
Publication year - 2003
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2003.043034
Subject(s) - utricle , depolarization , neuroscience , hair cell , biology , patch clamp , sodium channel , vestibular system , tetrodotoxin , electrophysiology , membrane potential , neurotrophin , inner ear , microbiology and biotechnology , chemistry , endocrinology , receptor , sodium , biochemistry , organic chemistry
The mammalian utricular sensory receptors are commonly believed to be non‐spiking cells with electrical activity limited to graded membrane potential changes. Here we provide evidence that during the first post‐natal week, the sensory hair cells of the rat utricle express a tetrodotoxin (TTX)‐sensitive voltage‐gated Na + current that displays most of the biophysical and pharmacological characteristics of neuronal Na + current. Single‐cell RT‐PCR reveals that several α‐subunit isoforms of the Na + channels are co‐expressed within a single hair cell, with a major expression of Nav1.2 and Nav1.6 subunits. In neonatal hair cells, 30 % of the Na + channels are available for activation at the resting potential. Depolarizing current injections in the range of the transduction currents are able to trigger TTX‐sensitive action potentials. We also provide evidence of a TTX‐sensitive activity‐dependent brain‐derived neurotrophic factor (BDNF) release by early post‐natal utricle explants. Developmental analysis shows that Na + currents decrease dramatically from post‐natal day 0 (P0) to P8 and become almost undetectable at P21. Concomitantly, depolarizing stimuli fail to induce both action potential and BDNF release at P20. The present findings reveal that vestibular hair cells express neuronal‐like TTX‐sensitive Na + channels able to generate Na + ‐driven action potentials only during the early post‐natal period of development. During the same period an activity‐dependent BDNF secretion by utricular explants has been demonstrated. This could be an important mechanism involved in vestibular sensory system differentiation and synaptogenesis.