European Neuroscience Institute, Deutsche Forschungsgemeinschaft Center for Molecular Physiology of the Brain/Excellence Cluster 171, 37077 Göttingen, Germany.
Proc Natl Acad Sci U S A. 2011 Oct 11;108(41):17183-8. doi: 10.1073/pnas.1112690108. Epub 2011 Sep 8.
Presynaptic nerve terminals contain between several hundred vesicles (for example in small CNS synapses) and several tens of thousands (as in neuromuscular junctions). Although it has long been assumed that such high numbers of vesicles are required to sustain neurotransmission during conditions of high demand, we found that activity in vivo requires the recycling of only a few percent of the vesicles. However, the maintenance of large amounts of reserve vesicles in many evolutionarily distinct species suggests that they are relevant for synaptic function. We suggest here that these vesicles constitute buffers for soluble accessory proteins involved in vesicle recycling, preventing their loss into the axon. Supporting this hypothesis, we found that vesicle clusters contain a large variety of proteins needed for vesicle recycling, but without an obvious function within the clusters. Disrupting the clusters by application of black widow spider venom resulted in the diffusion of numerous soluble proteins into the axons. Prolonged stimulation and ionomycin application had a similar effect, suggesting that calcium influx causes the unbinding of soluble proteins from vesicles. Confirming this hypothesis, we found that isolated synaptic vesicles in vitro sequestered soluble proteins from the cytosol in a process that was inhibited by calcium addition. We conclude that the reserve vesicles support neurotransmission indirectly, ensuring that soluble recycling proteins are delivered upon demand during synaptic activity.
突触前神经末梢含有数百个囊泡（例如在小脑中枢突触中）和数万到数十万囊泡（如在神经肌肉接头中）。尽管长期以来一直假设，在高需求条件下，需要如此多数量的囊泡来维持神经递质传递，但我们发现，体内的活动仅需要循环使用一小部分囊泡。然而，在许多进化上不同的物种中维持大量的储备囊泡表明它们与突触功能相关。在这里，我们提出这些囊泡构成了参与囊泡再循环的可溶性辅助蛋白的缓冲液，防止它们进入轴突。支持这一假说，我们发现囊泡簇包含大量用于囊泡再循环的蛋白质，但在簇内没有明显的功能。应用黑寡妇蜘蛛毒液破坏簇会导致大量可溶性蛋白扩散到轴突中。延长刺激和离子霉素处理也有类似的效果，表明钙内流导致可溶性蛋白从囊泡中解偶联。证实了这一假说，我们发现体外分离的突触小泡可以将可溶性蛋白从细胞质中隔离出来，而钙离子的加入会抑制这一过程。我们得出结论，储备囊泡间接支持神经递质传递，确保在突触活动期间按需提供可溶性再循环蛋白。
