Incomplete vesicular docking limits synaptic strength under high release probability conditions
- Washington University, United States
- Doshisha University, Japan
- Paris Descartes University, France
- Université de Paris, France
Abstract
Central mammalian synapses release synaptic vesicles in dedicated structures called docking/release sites. It has been assumed that when voltage-dependent calcium entry is sufficiently large, synaptic output attains a maximum value of one synaptic vesicle per action potential and per site. Here we use deconvolution to count synaptic vesicle output at single sites (mean site number per synapse: 3.6). When increasing calcium entry with tetraethylammonium in 1.5 mM external calcium concentration, we find that synaptic output saturates at 0.22 vesicle per site, not at 1 vesicle per site. Fitting the results with current models of calcium-dependent exocytosis indicates that the 0.22 vesicle limit reflects the probability of docking sites to be occupied by synaptic vesicles at rest, as only docked vesicles can be released. With 3 mM external calcium, the maximum output per site increases to 0.47, indicating an increase in docking site occupancy as a function of external calcium concentration.
Data availability
Igor files of the analysis, that contain the entire list of analysis operations are provided as Source Data 1.
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Funding
H2020 European Research Council (294509)
- Gerardo Malagon
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2020, Malagon et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Incomplete vesicular docking limits synaptic strength under high release probability conditions
eLife 9:e52137.
https://doi.org/10.7554/eLife.52137
