Synaptotagmin-1 and synaptotagmin-7 trigger synchronous and asynchronous phases of neurotransmitter release

Neuron. 2013 Nov 20;80(4):947-59. doi: 10.1016/j.neuron.2013.10.026.

Abstract

In forebrain neurons, knockout of synaptotagmin-1 blocks fast Ca(2+)-triggered synchronous neurotransmitter release but enables manifestation of slow Ca(2+)-triggered asynchronous release. Here, we show using single-cell PCR that individual hippocampal neurons abundantly coexpress two Ca(2+)-binding synaptotagmin isoforms, synaptotagmin-1 and synaptotagmin-7. In synaptotagmin-1-deficient synapses of excitatory and inhibitory neurons, loss of function of synaptotagmin-7 suppressed asynchronous release. This phenotype was rescued by wild-type but not mutant synaptotagmin-7 lacking functional Ca(2+)-binding sites. Even in synaptotagmin-1-containing neurons, synaptotagmin-7 ablation partly impaired asynchronous release induced by extended high-frequency stimulus trains. Synaptotagmins bind Ca(2+) via two C2 domains, the C2A and C2B domains. Surprisingly, synaptotagmin-7 function selectively required its C2A domain Ca(2+)-binding sites, whereas synaptotagmin-1 function required its C2B domain Ca(2+)-binding sites. Our data show that nearly all Ca(2+)-triggered release at a synapse is due to synaptotagmins, with synaptotagmin-7 mediating a slower form of Ca(2+)-triggered release that is normally occluded by faster synaptotagmin-1-induced release but becomes manifest upon synaptotagmin-1 deletion.

Publication types

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

MeSH terms

  • Animals
  • Calcium / physiology
  • Cells, Cultured
  • Dependovirus / genetics
  • Fluorescent Antibody Technique
  • Hippocampus / cytology
  • Hippocampus / physiology
  • Lentivirus / genetics
  • Mice
  • Mice, Knockout
  • Neurons / metabolism
  • Neurotransmitter Agents / metabolism*
  • Patch-Clamp Techniques
  • RNA Interference
  • RNA, Messenger / biosynthesis
  • RNA, Messenger / genetics
  • Receptors, Calcium-Sensing / physiology
  • Synapses / metabolism
  • Synaptotagmin I / genetics
  • Synaptotagmin I / physiology*
  • Synaptotagmins / genetics
  • Synaptotagmins / physiology*

Substances

  • Neurotransmitter Agents
  • RNA, Messenger
  • Receptors, Calcium-Sensing
  • Synaptotagmin I
  • Synaptotagmins
  • Calcium