High mobility of vesicles supports continuous exocytosis at a ribbon synapse
High mobility of vesicles supports continuous exocytosis at a ribbon synapse
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DOI：
10.1016/j.cub.2003.12.053
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发表时间：
2004-02-03
期刊：
影响因子：
9.2
通讯作者：
Lagnado, L
中科院分区：
文献类型：
--
作者：
Holt, M;Cooke, A;Lagnado, L
背景：大多数突触以瞬时脉冲的形式释放神经递质，但感觉神经元的带状突触支持持续的胞吐作用，以响应持续的刺激。我们研究了囊泡的移动和回收如何促进视网膜双极细胞带状突触的连续胞吐作用。结果：结合使用全内反射荧光显微镜和光漂白后的荧光恢复，我们发现质膜 50-120 nm 内的绝大多数囊泡以随机方式移动，有效扩散系数类似于 1.5 x 10(-2) mum(2) s(-1)。使用共聚焦显微镜，我们发现囊泡在整个末端类似地移动，并且这种运动不会因钙流入或肌动蛋白细胞骨架而改变。我们计算出，大约有 300,000 个囊泡的细胞质库将产生大约 900 次囊泡/秒与带的碰撞和 28,000 次/秒与表面膜的碰撞。通过电子显微镜证实了囊泡向带的有效再供应。 1 分钟去极化，释放 500-1000 个囊泡/秒，导致停靠在活性区的囊泡数量减少 70%，而不会减少附着在质膜带或远程区域的囊泡数量。这些位点没有被回收的囊泡重新填充，因为 80-90% 的回收膜被吸收到从表面夹断的池中。结论：这些结果表明，细胞质囊泡的随机运动为带和质膜提供了有效的供应，并允许维持高速率的胞吐作用，而无需同样快速的囊泡回收。停靠在带下的囊泡的选择性耗尽表明，囊泡向活性区的转移限制了维持刺激期间的胞吐速率。
Background: Most synapses release neurotransmitter as transient pulses, but ribbon synapses of sensory neurons support continuous exocytosis in response to maintained stimulation. We have investigated how the movement and retrieval of vesicles might contribute to continuous exocytosis at the ribbon synapse of retinal bipolar cells.Results: Using a combination of total internal reflection fluorescence microscopy and fluorescence recovery after photobleaching, we found that the great majority of vesicles within 50-120 nm of the plasma membrane move in a random fashion with an effective diffusion coefficient of similar to1.5 x 10(-2) mum(2) s(-1). Using confocal microscopy, we found that vesicles are similarly mobile across the whole terminal and that this motion is not altered by calcium influx or the actin cytoskeleton. We calculated that the cytoplasmic reservoir of similar to300,000 vesicles would generate about 900 vesicle collisions/s against ribbons and 28,000 collisions/s against the surface membrane. The efficient resupply of vesicles to ribbons was confirmed by electron microscopy. A 1 min depolarization, releasing 500-1000 vesicles/s, caused a 70% reduction in the number of vesicles docked at the active zone without reducing the number of vesicles attached to ribbons or remote areas of the plasma membrane. These sites were not repopulated by retrieved vesicles because 80-90% of the recycled membrane was taken up into cisternae that pinched off from the surface.Conclusions: These results indicate that the random motion of cytoplasmic vesicles provides an efficient supply to the ribbon and plasma membrane and allows the maintenance of high rates of exocytosis without an equally rapid recycling of vesicles. The selective depletion of vesicles docked under ribbons suggests that the transfer of vesicles to the active zone limits the rate of exocytosis during maintained stimulation.