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A dual-Ca2+-sensor model for neurotransmitter release in a central synapse

Nature volume 450, pages 676–682 (2007)Cite this article

Abstract

Ca2+-triggered synchronous neurotransmitter release is well described, but asynchronous release—in fact, its very existence—remains enigmatic. Here we report a quantitative description of asynchronous neurotransmitter release in calyx-of-Held synapses. We show that deletion of synaptotagmin 2 (Syt2) in mice selectively abolishes synchronous release, allowing us to study pure asynchronous release in isolation. Using photolysis experiments of caged Ca2+, we demonstrate that asynchronous release displays a Ca2+ cooperativity of ∼2 with a Ca2+ affinity of ∼44 μM, in contrast to synchronous release, which exhibits a Ca2+ cooperativity of ∼5 with a Ca2+ affinity of ∼38 μM. Our results reveal that release triggered in wild-type synapses at low Ca2+ concentrations is physiologically asynchronous, and that asynchronous release completely empties the readily releasable pool of vesicles during sustained elevations of Ca2+. We propose a dual-Ca2+-sensor model of release that quantitatively describes the contributions of synchronous and asynchronous release under conditions of different presynaptic Ca2+ dynamics.

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Figure 1: Calyx synapses in Syt2-deficient mice.
Figure 2: Synaptic transmission evoked by isolated action potentials.
Figure 3: RRP size, Ca 2+  currents and release kinetics in Syt2-deficient calyx synapses.
Figure 4: Relationship between peak vesicular release rates and [Ca2+]i in calyx terminals.
Figure 5: A dual-Ca 2+ -sensor model for neurotransmitter release.

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Acknowledgements

We thank I. Kornblum, A. Roth, L. Fan and J. Mitchell for excellent technical assistance, and J. Bollmann, X. Lou and R. Schneggenburger for advice. This study was supported by a grant from NARSAD (to J.S.) and by The University of Texas M. D. Anderson Cancer Center Physician Scientist Program (R.A.).

Author Contributions J.S. performed the electrophysiology and photolysis experiments and modelling. Z.P.P. carried out the biochemical, immunohistochemical, and mouse genetics experiments; D.Q. participated in the electrophysiology and photolysis experiments; A.T. F. and R.A. generated the Syt2 knockout mice, and T.C.S. and J.S. designed the experiments and wrote the manuscript.

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Authors and Affiliations

  1. Departments of Neuroscience and,, Texas

    Jianyuan Sun, Zhiping P. Pang, Dengkui Qin & Thomas C. Südhof

  2. Molecular Genetics, and,, Texas

    Jianyuan Sun & Thomas C. Südhof

  3. Howard Hughes Medical Institute, The University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA , Texas

    Thomas C. Südhof

  4. Department of Pulmonary Medicine, The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA, Texas

    Abigail T. Fahim & Roberto Adachi

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  1. Jianyuan Sun
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Correspondence to Jianyuan Sun or Thomas C. Südhof.

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The file contains Supplementary Methods with additional references, Supplementary Tables 1-2 and Supplementary Figures 1-14 with Legends. (PDF 1893 kb)

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Sun, J., Pang, Z., Qin, D. et al. A dual-Ca2+-sensor model for neurotransmitter release in a central synapse. Nature 450, 676–682 (2007). https://doi.org/10.1038/nature06308

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