Nature：神经传输物质的释放
神经传输物质在神经末梢的释放是由钙离子的流入触发的，其流入是响应于神经脉冲进行的——可以是自然进行的， 也可以是作为动作电位进行的。在后一种情况下，释放是快速的（和同步的）或延迟的（非同步的）。Jianyuan Sun等人利用遗传学和电生理学工具，将同步和非同步释放区分了开来，并且提出二者存在独立的钙传感器。他们还建立了一个定量模型，来解释突触传输的钙依赖性的所有情况。
原始出处:
Nature 450, 676-682 (29 November 2007) | doi:10.1038/nature06308; Received 20 August 2007; Accepted 24 September 2007
A dual-Ca2+-sensor model for neurotransmitter release in a central synapse
Jianyuan Sun1,2, Zhiping P. Pang1, Dengkui Qin1, Abigail T. Fahim4, Roberto Adachi4 & Thomas C. Südhof1,2,3
- Departments of Neuroscience and,
- Molecular Genetics, and,
- Howard Hughes Medical Institute, The University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Pulmonary Medicine, The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA
Correspondence to: Jianyuan Sun1,2Thomas C. Südhof1,2,3 Correspondence and requests for materials should be addressed to J.S. (Email: Jianyuan.Sun@UTSouthwestern.edu) or T.C.S. (Email: Thomas.Sudhof@UTSouthwestern.edu).
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 
M, in contrast to synchronous release, which exhibits a Ca2+ cooperativity of 5 with a Ca2+ affinity of 38 M. 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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