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Synaptotagmin-1 functions as a Ca2+ sensor for spontaneous release.

Jun Xu1, Zhiping P Pang, Ok-Ho Shin

  • 1Department of Molecular & Cellular Physiology, Stanford University, Palo Alto, California, USA.

Nature Neuroscience
|May 5, 2009
PubMed
Summary

Spontaneous neurotransmitter release primarily uses synaptotagmin-1 (Syt1), the same Ca2+ sensor for evoked release. However, Syt1 also acts as a clamp, preventing excessive spontaneous release via a separate, more sensitive Ca2+ sensor.

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Area of Science:

  • Neuroscience
  • Molecular Biology
  • Synaptic Transmission

Background:

  • Spontaneous neurotransmitter release is a fundamental synaptic process.
  • The molecular mechanisms governing spontaneous release remain incompletely understood.
  • Synaptotagmin-1 (Syt1) is known as the Ca2+ sensor for fast, evoked neurotransmitter release.

Purpose of the Study:

  • To elucidate the role of synaptotagmin-1 (Syt1) in spontaneous neurotransmitter release.
  • To investigate the relationship between the Ca2+ sensing mechanisms of spontaneous and evoked release.
  • To understand how Syt1 regulates synaptic vesicle exocytosis.

Main Methods:

  • Utilized murine cortical neurons.
  • Investigated spontaneous and evoked neurotransmitter release.
  • Employed Syt1 mutations and deletions to assess Ca2+ affinity and cooperativity.
  • Analyzed Ca2+ dependence of release events.

Main Results:

  • Over 95% of spontaneous release is Ca2+-dependent and mediated by Syt1.
  • Syt1 mutations affecting Ca2+ affinity proportionally altered both spontaneous and evoked release.
  • Syt1 deletions paradoxically increased spontaneous release, revealing a Ca2+-dependent but lower-affinity/cooperativity sensor.
  • Syt1 acts as both an activator and a clamp for spontaneous release.

Conclusions:

  • Spontaneous and evoked neurotransmitter release share the same primary Ca2+-dependent release machinery involving Syt1.
  • Syt1 functions not only as a Ca2+ sensor but also as a clamp, regulating a distinct, more sensitive Ca2+ sensor for spontaneous release.
  • These findings reveal a dual role for Syt1 in controlling both spontaneous and evoked exocytosis at the synapse.