分类： 生物学 >> 生物物理学 提交时间： 2016-05-12
摘要： Vesicle recycling is pivotal for maintaining reliable synaptic signaling, but its basic properties remain poorly understood. Here, we developed an approach to quantitatively analyze the kinetics of vesicle recycling with exquisite signal and temporal resolution at the calyx of Held synapse. The combination of this electrophysiological approach with electron microscopy revealed that similar to 80% of vesicles (similar to 270,000 out of similar to 330,000) in the nerve terminal are involved in recycling. Under sustained stimulation, recycled vesicles start to be reused in tens of seconds when similar to 47% of the preserved vesicles in the recycling pool (RP) are depleted. The heterogeneity of vesicle recycling as well as two kinetic components of RP depletion revealed the existence of a replenishable pool of vesicles before the priming stage and led to a realistic kinetic model that assesses the size of the subpools of the RP. Thus, our study quantified the kinetics of vesicle recycling and kinetically dissected the whole vesicle pool in the calyceal terminal into the readily releasable pool (similar to 0.6%), the readily priming pool (similar to 46%), the premature pool (similar to 33%), and the resting pool (similar to 20%).
分类： 生物学 >> 生物物理学 >> 神经科学 提交时间： 2016-05-11
Dai, Jinye
Chen, Peihua
Tian, Hao
Sun, Jianyuan
Dai, Jinye
Tian, Hao
Sun, Jianyuan
Chen, Peihua
Sun, Jianyuan
摘要： It is well known that voltage-gated calcium channels (VGCCs)-mediated Ca2+ influx triggers evoked synaptic vesicle release. However, the mechanisms of Ca2+ regulation of spontaneous miniature vesicle release (mini) remain poorly understood. Here we show that blocking VGCCs at the juvenile mice (C57BL/6) calyx of Held synapse failed to cause an immediate change in minis. Instead, it resulted in a significant reduction (similar to 40%) of mini frequency several minutes after the blockage. By recording VGCC activity and single vesicle fusion events directly at the presynaptic terminal, we found that minis did not couple to VGCC-mediated Ca2+ entry, arguing for a lack of direct correlation between mini and transient Ca2+ influx. Moreover, mini frequencies displayed a lower apparent Ca2+ cooperativity than those of evoked release. In agreement with this observation, abrogation of the Ca2+ sensor synaptotagmin-2 had no effect on apparent Ca2+ cooperativity of minis. Together, our study provides the first direct evidence that spontaneous minis are not mediated by transient Ca2+ signals through VGCCs and are triggered by a Ca2+-sensing mechanism that is different from the evoked release at these microdomain VGCC-vesicle coupled synapses.
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