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Compound vesicle fusion increases quantal size and potentiates synaptic transmission

Nature volume 459, pages 9397 (07 May 2009) | Download Citation

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Abstract

Exocytosis at synapses involves fusion between vesicles and the plasma membrane1. Although compound fusion between vesicles2,3 was proposed to occur at ribbon-type synapses4,5, whether it exists, how it is mediated, and what role it plays at conventional synapses remain unclear. Here we report the existence of compound fusion, its underlying mechanism, and its role at a nerve terminal containing conventional active zones in rats and mice. We found that high potassium application and high frequency firing induced giant capacitance up-steps, reflecting exocytosis of vesicles larger than regular ones, followed by giant down-steps, reflecting bulk endocytosis. These intense stimuli also induced giant vesicle-like structures, as observed with electron microscopy, and giant miniature excitatory postsynaptic currents (mEPSCs), reflecting more transmitter release. Calcium and its sensor for vesicle fusion, synaptotagmin, were required for these giant events. After high frequency firing, calcium/synaptotagmin-dependent mEPSC size increase was paralleled by calcium/synaptotagmin-dependent post-tetanic potentiation. These results suggest a new route of exocytosis and endocytosis composed of three steps. First, calcium/synaptotagmin mediates compound fusion between vesicles. Second, exocytosis of compound vesicles increases quantal size, which increases synaptic strength and contributes to the generation of post-tetanic potentiation. Third, exocytosed compound vesicles are retrieved via bulk endocytosis. We suggest that this vesicle cycling route be included in models of synapses in which only vesicle fusion with the plasma membrane is considered1.

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Change history

  • 07 May 2009

    Error bars were added to the third panel of Fig. 4a on 7 May 2009.

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Acknowledgements

We thank J. Diamond and K. Paradiso for comments on the manuscript, and S. Cheng, R. Azzam and V. Crocker for help in EM. This work was supported by the National Institute of Neurological Disorders and Stroke Intramural Research Program (L.-G.W.) and the American Heart Association (R.A.).

Author Contributions L.H. performed cell-attached recordings; L.X. performed EM work, and the mEPSC and EPSC recordings; J.X. and B.D.M. helped with some experiments; L.B. helped with EM work and maintained Syt2-/- mice; E.M. and R.A. generated the Syt2-/- mouse line; and L.-G.W. supervised the project and wrote the paper.

Author information

Author notes

    • Liming He
    •  & Lei Xue

    These authors contributed equally to this work.

Affiliations

  1. National Institute of Neurological Disorders and Stroke, 35 Convent Drive, Building 35, Room 2B-1012, Bethesda, Maryland 20892, USA

    • Liming He
    • , Lei Xue
    • , Jianhua Xu
    • , Benjamin D. McNeil
    • , Li Bai
    •  & Ling-Gang Wu
  2. Department of Pulmonary Medicine, The University of Texas M. D. Anderson Cancer Center, 2121 West Holcombe Boulevard, Box 1100, Houston, Texas 77030, USA

    • Ernestina Melicoff
    •  & Roberto Adachi

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Corresponding author

Correspondence to Ling-Gang Wu.

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    Supplementary Information

    This file contains Supplementary Notes, Supplementary Results, Supplementary Methods, Supplementary Figures S1-S8 with Legends and Supplementary References

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https://doi.org/10.1038/nature07860

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