Allosteric modulation of the presynaptic Ca2+ sensor for vesicle fusion

Nature. 2005 May 26;435(7041):497-501. doi: 10.1038/nature03568.


Neurotransmitter release is triggered by an increase in the cytosolic Ca2+ concentration ([Ca2+]i), but it is unknown whether the Ca2+-sensitivity of vesicle fusion is modulated during synaptic plasticity. We investigated whether the potentiation of neurotransmitter release by phorbol esters, which target presynaptic protein kinase C (PKC)/munc-13 signalling cascades, exerts a direct effect on the Ca2+-sensitivity of vesicle fusion. Using direct presynaptic Ca2+-manipulation and Ca2+ uncaging at a giant presynaptic terminal, the calyx of Held, we show that phorbol esters potentiate transmitter release by increasing the apparent Ca2+-sensitivity of vesicle fusion. Phorbol esters potentiate Ca2+-evoked release as well as the spontaneous release rate. We explain both effects by an increased fusion 'willingness' in a new allosteric model of Ca2+-activation of vesicle fusion. In agreement with an allosteric mechanism, we observe that the classically high Ca2+ cooperativity in triggering vesicle fusion (approximately 4) is gradually reduced below 3 microM [Ca2+]i, reaching a value of <1 at basal [Ca2+]i. Our data indicate that spontaneous transmitter release close to resting [Ca2+]i is a consequence of an intrinsic property of the molecular machinery that mediates synaptic vesicle fusion.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Allosteric Regulation / drug effects
  • Animals
  • Brain Stem / cytology
  • Brain Stem / drug effects
  • Brain Stem / physiology
  • Calcium / metabolism*
  • Calcium / pharmacology
  • Calcium Signaling / drug effects
  • Chromaffin Cells / cytology
  • Chromaffin Cells / drug effects
  • Chromaffin Cells / metabolism
  • Excitatory Postsynaptic Potentials / physiology
  • In Vitro Techniques
  • Membrane Fusion* / drug effects
  • Models, Biological
  • Neurotransmitter Agents / metabolism*
  • Phorbol 12,13-Dibutyrate / pharmacology
  • Presynaptic Terminals / drug effects
  • Presynaptic Terminals / metabolism*
  • Rats
  • Synapses / drug effects
  • Synapses / metabolism*
  • Synaptic Transmission / drug effects


  • Neurotransmitter Agents
  • Phorbol 12,13-Dibutyrate
  • Calcium