Calcium dependence of exocytosis and endocytosis at the cochlear inner hair cell afferent synapse

Neuron. 2001 Mar;29(3):681-90. doi: 10.1016/s0896-6273(01)00243-4.


Release of neurotransmitter at the inner hair cell (IHC) afferent synapse is a fundamental step in translating sound into auditory nerve excitation. To study the Ca2+ dependence of the underlying vesicle fusion and subsequent endocytosis, we combined Ca2+ uncaging with membrane capacitance measurements in mouse IHCs. Rapid elevations in [Ca2+]i above 8 microM caused a biphasic capacitance increase corresponding to the fusion of approximately 40,000 vesicles. The kinetics of exocytosis displayed a fifth-order Ca2+ dependence reaching maximal rates of >3 x 10(7) vesicle/s. Exocytosis was always followed by slow, compensatory endocytosis (tau congruent with 15 s). Higher [Ca2+]i increased the contribution of a faster mode of endocytosis with a Ca2+ independent time constant of approximately 300 ms. These properties provide for rapid and sustained transmitter release from this large presynaptic terminal.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism
  • Calcium / pharmacology
  • Calcium / physiology*
  • Calcium Channels / physiology
  • Cell Membrane / physiology
  • Electric Conductivity
  • Endocytosis / physiology*
  • Exocytosis / physiology*
  • Hair Cells, Auditory, Inner / physiology*
  • Ion Channel Gating / physiology
  • Kinetics
  • Mice
  • Neurotransmitter Agents / metabolism
  • Photolysis
  • Synapses / physiology*


  • Calcium Channels
  • Neurotransmitter Agents
  • Calcium