External Ca2+ dependency of synaptic transmission in drosophila synaptotagmin I mutants.
External Ca2+ dependency of synaptic transmission in drosophila synaptotagmin I mutants.
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DOI：
10.1152/jn.00205.2005
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发表时间：
2005-08
影响因子：
2.5
通讯作者：
T. Okamoto;T. Tamura;Kazuhiro Suzuki;Y. Kidokoro
中科院分区：
文献类型：
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作者：
T. Okamoto;T. Tamura;Kazuhiro Suzuki;Y. Kidokoro
为了解决关于Synaptotagmin I （Syt I）功能报道的一些差异，我们重新检查了Syt I基因（Syt I）突变的果蝇胚胎神经肌肉连接处的突触传递。两个主要的问题是Ca2+结合域，C2A或C2B，感知Ca2+和Syt I是自发囊泡融合的负调节因子。神经刺激或高K+处理在含有不同Ca2+浓度的外溶液中诱导突触电流。在零等位基因syt I（AD4）中，同步突触电流很少被观察到，但并未被消除。量子含量约为对照的1/60，但随着[Ca2+](e)的增加呈线性增加，双对数图斜率为0.95 (N)，而对照为3.01。缺少第二个Ca2+结合结构域C2B的等位基因syt I（AD1）的斜率为1.06，与syt I（AD4）的斜率无显著差异。在另一个等位基因syt I（AD3）中，C2B的一个氨基酸发生突变，同步突触传递也受损，N为1.54，显著小于对照组。在高K+生理盐水中，syt I（AD4）中[Ca2+](e)对囊泡释放的依赖性低于对照组，而syt I（AD3）中的[Ca2+](e)依赖性甚至低于syt I(AD4)，提示syt I（AD3）抑制囊泡融合。这些发现使我们得出结论，C2B而不是C2A感知Ca2+， Syt I是囊泡融合的负调节因子。
To resolve some of differences in reports on the function of Synaptotagmin I (Syt I), we re-examined synaptic transmission at the neuromuscular junction of Drosophila embryos that have mutations in the Syt I gene (syt I). Two major questions addressed were which Ca2+ binding domain, C2A or C2B, sense Ca2+ and is Syt I a negative regulator of spontaneous vesicle fusion. Synaptic currents were induced by nerve stimulation or by high K+ treatment in external solutions containing various Ca2+ concentrations. In a null allele, syt I(AD4), synchronous synaptic currents were rarely observed but not abolished. The quantal content was about 1/60 of control but increased linearly with [Ca2+](e) with a slope of 0.95 (N) in the double logarithmic plot, in contrast to 3.01 in control. The slope of 1.06 in an allele, syt I(AD1), which lacks the second Ca2+ binding domain, C2B, was not different from in syt I(AD4). In another allele, syt I(AD3), in which one amino acid in C2B is mutated, synchronous synaptic transmission was also impaired and N was 1.54, which is significantly smaller than in control. In high K+ saline, the [Ca2+](e) dependency of vesicle release in syt I(AD4) was lower than in controls, whereas that in syt I(AD3) was even lower than in syt I(AD4), suggesting that syt I(AD3) is inhibiting vesicle fusion. These findings led us to conclude that C2B, not C2A, senses Ca2+, and Syt I is a negative regulator of vesicle fusion.