The role of endocytosis in regulating the strength of hippocampal synapses
The role of endocytosis in regulating the strength of hippocampal synapses
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DOI：
10.1113/jphysiol.2008.159715
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发表时间：
2008-12-15
影响因子：
5.5
通讯作者：
Lagnado, Leon
中科院分区：
文献类型：
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作者：
Granseth, Bjoern;Lagnado, Leon
在突触活动期间，容易释放的囊泡池(RRP)的大小不同，并通过从储备池中重新招募以及融合后的囊泡回收来补充。为了研究这些步骤中哪些是向RRP供应囊泡的速率限制，我们测量了培养的海马神经元中温度变化的影响，在培养的海马神经元中，随着温度的升高，可以保持更高的平均释放速率。使用基于pHluorin的胞吐和内吞作用的报告(SypHy)，我们发现温度在25摄氏度到35摄氏度之间的变化不会显著改变从储备池中招募的速度。而囊泡再酸化时间常数则由接近1 S(Q(10)=5.5)降至接近1 S(Q(10)=5.5)。使用测量参数建立的囊泡周期动力学模型被发现描述了在长时间的棘波序列中观察到的囊泡释放速率的变化，以及在突触活动爆发后从突触抑制中恢复的变化。这些结果表明，内吞作用以10-15的时间常数运行，S是决定长期活动期间RRP补充的限速过程。在任何温度下都不能检测到快速的囊泡恢复模式，也没有必要调用这样的机制来解释突触释放概率的使用依赖变化。
The readily releasable pool of vesicles (RRP) varies in size during synaptic activity and is replenished by recruitment from the reserve pool as well as vesicle retrieval after fusion. To investigate which of these steps is rate limiting in supplying vesicles to the RRP, we measured the effects of changes in temperature in cultured hippocampal neurons, where higher average rates of release can be maintained as the temperature is increased. Using a pHluorin-based reporter of exocytosis and endocytosis (sypHy), we find that changes in temperature between 25 degrees C and 35 degrees C do not significantly alter the rate of recruitment from the reserve pool. In contrast, the time constant of endocytosis fell from similar to 17 s at 25 degrees C to similar to 10 s at 35 degrees C (Q(10) = 1.7), while the time constant of vesicle reacidification fell from similar to 5.5 s to similar to 1 s (Q(10) = 5.5). A kinetic model of the vesicle cycle constructed using measured parameters was found to describe variations in vesicle release rate observed during long trains of spikes as well as recovery from synaptic depression after bursts of activity. These results indicate that endocytosis operating with time constants of 10-15 s is the rate-limiting process determining replenishment of the RRP during long-term activity. A fast mode of vesicle retrieval could not be detected at any temperature, nor was it necessary to invoke such a mechanism to account for use-dependent changes in synaptic release probability.