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Proc Natl Acad Sci U S A. 2017 Jun 27;114(26):E5246-E5255. doi: 10.1073/pnas.1704470114. Epub 2017 Jun 12.

Numbers of presynaptic Ca2+ channel clusters match those of functionally defined vesicular docking sites in single central synapses.

Author information

1
Laboratoire de Physiologie Cérébrale, CNRS UMR 8118, Université Paris Descartes, 75006 Paris, France; takafumi.miki@parisdescartes.fr ryuichi.shigemoto@ist.ac.at alain.marty@parisdescartes.fr.
2
Institute of Science and Technology Austria, A-3400 Klosterneuburg, Austria.
3
Laboratoire de Physiologie Cérébrale, CNRS UMR 8118, Université Paris Descartes, 75006 Paris, France.
4
Department of Molecular and Cellular Physiology, Shinshu University School of Medicine, Matsumoto 390-8621, Japan.
5
Institute for Biomedical Sciences, Interdisciplinary Cluster for Cutting Edge Research, Shinshu University, Matsumoto 390-8621, Japan.
6
Department of Anatomy, Graduate School of Medicine, Hokkaido University, Sapporo 060-8638, Japan.
7
Institute of Science and Technology Austria, A-3400 Klosterneuburg, Austria; takafumi.miki@parisdescartes.fr ryuichi.shigemoto@ist.ac.at alain.marty@parisdescartes.fr.

Abstract

Many central synapses contain a single presynaptic active zone and a single postsynaptic density. Vesicular release statistics at such "simple synapses" indicate that they contain a small complement of docking sites where vesicles repetitively dock and fuse. In this work, we investigate functional and morphological aspects of docking sites at simple synapses made between cerebellar parallel fibers and molecular layer interneurons. Using immunogold labeling of SDS-treated freeze-fracture replicas, we find that Cav2.1 channels form several clusters per active zone with about nine channels per cluster. The mean value and range of intersynaptic variation are similar for Cav2.1 cluster numbers and for functional estimates of docking-site numbers obtained from the maximum numbers of released vesicles per action potential. Both numbers grow in relation with synaptic size and decrease by a similar extent with age between 2 wk and 4 wk postnatal. Thus, the mean docking-site numbers were 3.15 at 2 wk (range: 1-10) and 2.03 at 4 wk (range: 1-4), whereas the mean numbers of Cav2.1 clusters were 2.84 at 2 wk (range: 1-8) and 2.37 at 4 wk (range: 1-5). These changes were accompanied by decreases of miniature current amplitude (from 93 pA to 56 pA), active-zone surface area (from 0.0427 μm2 to 0.0234 μm2), and initial success rate (from 0.609 to 0.353), indicating a tightening of synaptic transmission with development. Altogether, these results suggest a close correspondence between the number of functionally defined vesicular docking sites and that of clusters of voltage-gated calcium channels.

KEYWORDS:

active zone; calcium channel; neurotransmitter release; parallel fiber; release site

PMID:
28607047
PMCID:
PMC5495264
DOI:
10.1073/pnas.1704470114
[Indexed for MEDLINE]
Free PMC Article

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