Molecular Dynamics of Synaptic Function Laboratory, Queensland Brain Institute and School of Biomedical Sciences, The University of Queensland, Brisbane, QLD 4072, Australia.
J Cell Sci. 2010 Apr 1;123(Pt 7):1131-40. doi: 10.1242/jcs.049296. Epub 2010 Mar 9.
Glycerotoxin (GLTx), a large neurotoxin isolated from the venom of the sea worm Glycera convoluta, promotes a long-lasting increase in spontaneous neurotransmitter release at the peripheral and central synapses by selective activation of Ca(v)2.2 channels. We found that GLTx stimulates the very high frequency, long-lasting (more than 10 hours) spontaneous release of acetylcholine by promoting nerve terminal Ca(2+) oscillations sensitive to the inhibitor omega-conotoxin GVIA at the amphibian neuromuscular junction. Although an estimate of the number of synaptic vesicles undergoing exocytosis largely exceeds the number of vesicles present in the motor nerve terminal, ultrastructural examination of GLTx-treated synapses revealed no significant change in the number of synaptic vesicles. However, we did detect the appearance of large pre-synaptic cisternae suggestive of bulk endocytosis. Using a combination of styryl dyes, photoconversion and horseradish peroxidase (HRP)-labeling electron microscopy, we demonstrate that GLTx upregulates presynaptic-vesicle recycling, which is likely to emanate from the limiting membrane of these large cisternae. Similar synaptic-vesicle recycling through bulk endocytosis also occurs from nerve terminals stimulated by high potassium. Our results suggest that this process might therefore contribute significantly to synaptic recycling under sustained levels of synaptic stimulation.
甘油毒素 (GLTx) 是从海蚯蚓 Glycera convoluta 的毒液中分离出来的一种大型神经毒素,通过选择性激活 Ca(v)2.2 通道,促进外周和中枢突触中自发性神经递质释放的持久增加。我们发现,GLTx 通过促进对抑制剂 ω-芋螺毒素 GVIA 敏感的神经末梢 Ca(2+) 振荡,刺激乙酰胆碱的超高频率、持久(超过 10 小时)自发性释放。尽管估计经历胞吐作用的突触小泡数量大大超过运动神经末梢中存在的小泡数量,但对 GLTx 处理的突触进行超微结构检查并未发现突触小泡数量有明显变化。然而,我们确实检测到大的前突触小泡出现,提示大体积内吞作用。使用组合的苯乙烯染料、光转化和辣根过氧化物酶 (HRP) -标记电子显微镜,我们证明 GLTx 上调了突触前小泡的再循环,这可能源于这些大小泡的限制膜。通过大体积内吞作用也会发生类似的突触小泡再循环,这是由高钾刺激的神经末梢引起的。我们的结果表明,这个过程可能会在持续的突触刺激水平下对突触再循环做出重大贡献。