Calcium dependence of exocytosis and endocytosis at the cochlear inner hair cell afferent synapse.
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.
Beutner
D
D
Department of Membrane Biophysics, Max-Planck-Institute for Biophysical Chemistry, Am Fassberg, 37077, Göttingen, Germany. dbeutne@gwdg.de
Voets
T
T
Neher
E
E
Moser
T
T
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology; D002462:Cell Membrane / Q000502:physiology; D004553:Electric Conductivity; D004705:Endocytosis / Q000502:physiology*; D005089:Exocytosis / Q000502:physiology*; D006199:Hair Cells, Auditory, Inner / Q000502:physiology*; D015640:Ion Channel Gating / Q000502:physiology; D007700:Kinetics; D051379:Mice; D018377:Neurotransmitter Agents / Q000378:metabolism; D010782:Photolysis; D013569:Synapses / Q000502:physiology*
D015220:Calcium Channels; D018377:Neurotransmitter Agents; D002118:Calcium