Expansion of calcium microdomains regulates fast exocytosis at a ribbon synapse
Expansion of calcium microdomains regulates fast exocytosis at a ribbon synapse
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DOI：
10.1073/pnas.0501961102
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发表时间：
2005-07-26
影响因子：
11.1
通讯作者：
Lagnado, L
中科院分区：
文献类型：
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作者：
Beaumont, V;Llobet, A;Lagnado, L
我们研究了Ca 2+信号调节快速胞吐在带状突触的视网膜双极细胞通过使用全内反射荧光显微镜图像荧光Ca 2+指标和干涉反射显微镜监测胞吐。去极化产生的Ca 2+“微区”，其在释放囊泡的快速释放池（RRP）（< 40 ms）的时间尺度上扩展。用10 mM EGTA替换末端中的移动的Ca 2+缓冲液可防止微区的扩张，并使快速释放囊泡的数量减少2倍。相反，降低EGTA在终端的浓度为0.1 mM增加了Ca 2+微区的表观宽度从580 nm到930 nm，并增加了1.5倍的RRP大小的大小。在微区扩展的区域上的[Ca 2 +]估计为2-7 μ M。这些结果表明，囊泡内的RRP位于数百纳米的Ca 2+通道，这些囊泡的融合可以触发低微摩尔水平的Ca 2+。因此，在活性区停靠囊泡和Ca 2+通道之间的可变距离为包含RRP的囊泡的异质释放概率提供了解释。
We investigated the Ca2+ signal regulating fast exocytosis at the ribbon synapse of retinal bipolar cells by using total internal reflection fluorescence microscopy to image fluorescent Ca2+ indicators and interference reflection microscopy to monitor exocytosis. Depolarization generated Ca2+ "microdomains" that expanded over the time scale during which the rapidly releasable pool (RRP) of vesicles was released (< 40 ms). Replacing mobile Ca2+ buffers in the terminal with 10 mM EGTA prevented expansion of microdomains and decreased the number of rapidly releasable vesicles by a factor of 2. Conversely, decreasing the concentration of EGTA in the terminal to 0.1 mM increased the apparent width of a Ca2+ microdomain from 580 nm to 930 nm and increased the size of the RRP size by a factor of 1.5. The [Ca2+] over the area that the microdomain expanded was estimated to be 2-7 mu M. These results indicate that vesicles within the RRP are located hundreds of nanometers from Ca2+ channels, and that fusion of these vesicles can be triggered by low micromolar levels of Ca2+. Variable distances between docked vesicles and Ca2+ channels at the active zone, therefore, provide an explanation for the heterogeneous release probability of vesicles comprising the RRP.