Otoferlin is critical for a highly sensitive and linear calcium-dependent exocytosis at vestibular hair cell ribbon synapses

J Neurosci. 2009 Aug 26;29(34):10474-87. doi: 10.1523/JNEUROSCI.1009-09.2009.

Abstract

Otoferlin, a C2-domain-containing Ca(2+) binding protein, is required for synaptic exocytosis in auditory hair cells. However, its exact role remains essentially unknown. Intriguingly enough, no balance defect has been observed in otoferlin-deficient (Otof(-/-)) mice. Here, we show that the vestibular nerve compound action potentials evoked during transient linear acceleration ramps in Otof(-/-) mice display higher threshold, lower amplitude, and increased latency compared with wild-type mice. Using patch-clamp capacitance measurement in intact utricles, we show that type I and type II hair cells display a remarkable linear transfer function between Ca(2+) entry, flowing through voltage-activated Ca(2+) channels, and exocytosis. This linear Ca(2+) dependence was observed when changing the Ca(2+) channel open probability or the Ca(2+) flux per channel during various test potentials. In Otof(-/-) hair cells, exocytosis displays slower kinetics, reduced Ca(2+) sensitivity, and nonlinear Ca(2+) dependence, despite morphologically normal synapses and normal Ca(2+) currents. We conclude that otoferlin is essential for a high-affinity Ca(2+) sensor function that allows efficient and linear encoding of low-intensity stimuli at the vestibular hair cell synapse.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acceleration
  • Action Potentials / drug effects
  • Action Potentials / physiology
  • Analysis of Variance
  • Animals
  • Animals, Newborn
  • Biophysics
  • Calcium / metabolism*
  • Calcium Channel Blockers / pharmacology
  • Chelating Agents / pharmacology
  • Egtazic Acid / analogs & derivatives
  • Egtazic Acid / pharmacology
  • Excitatory Postsynaptic Potentials / drug effects
  • Excitatory Postsynaptic Potentials / physiology
  • Exocytosis / drug effects
  • Exocytosis / genetics
  • Exocytosis / physiology*
  • Hair Cells, Vestibular / classification
  • Hair Cells, Vestibular / cytology*
  • Hair Cells, Vestibular / drug effects
  • Hair Cells, Vestibular / physiology
  • Linear Models
  • Membrane Proteins / deficiency
  • Membrane Proteins / physiology*
  • Mice
  • Mice, Knockout
  • Microscopy, Confocal
  • Microscopy, Electron, Transmission
  • Myosin VIIa
  • Myosins / metabolism
  • Patch-Clamp Techniques / methods
  • Reaction Time / drug effects
  • Reaction Time / physiology
  • Receptors, AMPA / metabolism
  • Synapses / drug effects
  • Synapses / genetics
  • Synapses / physiology*
  • Synapses / ultrastructure
  • Tetrodotoxin / pharmacology
  • Vestibular Nerve / physiology

Substances

  • Calcium Channel Blockers
  • Chelating Agents
  • Membrane Proteins
  • Myo7a protein, mouse
  • Myosin VIIa
  • Receptors, AMPA
  • otoferlin protein, mouse
  • Tetrodotoxin
  • Egtazic Acid
  • Myosins
  • 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid
  • glutamate receptor ionotropic, AMPA 2
  • Calcium