Synaptic depression and the kinetics of exocytosis in retinal bipolar cells
Synaptic depression and the kinetics of exocytosis in retinal bipolar cells
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DOI：
10.1523/jneurosci.20-02-00568.2000
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发表时间：
2000-01-15
影响因子：
5.3
通讯作者：
Lagnado, L
中科院分区：
文献类型：
--
作者：
Burrone, J;Lagnado, L
用电容技术研究了金鱼视网膜去极化双极细胞带突触的胞吐现象。当Ca2+电流被强烈激活时，快速释放囊泡池（RRP）以类似于300-500秒（-1）的单一速率常数释放。然而，当Ca2+电流在生理范围内（-45 ~ -25 mV）被去极化激活时，RRP的胞外分泌分两个阶段发生。在释放20%或更多的RRP后，胞吐速率常数下降了4-10倍。因此，突触抑制是由于对Ca2+内流的敏感性降低以及RRP的简单消耗引起的。在静息状态下，胞吐率随Ca2+电流的振幅增加到2的幂而变化。在抑制状态下，对Ca2+内流的敏感性降低了大约四倍。在生理范围内，每2.1 mV去极化，胞吐的初始阶段加速e倍，在-25 mV下平均120秒（-1）。因此，去极化双极细胞的突触以类似高通滤波器的方式响应阶跃去极化。这种转变似乎是由对Ca2+内流具有不同敏感性的快速释放囊泡的存在决定的。如果囊泡停靠在离Ca2+通道不同距离的质膜上，则可能发生这种情况。这些结果提示去极化双极细胞的带状突触可能是视网膜中的一个适应位点。
The capacitance technique was used to investigate exocytosis at the ribbon synapse of depolarizing bipolar cells from the goldfish retina. When the Ca2+ current was activated strongly, the rapidly releasable pool of vesicles (RRP) was released with a single rate-constant of similar to 300-500 sec(-1). However, when the Ca2+ current was activated weakly by depolarization in the physiological range (-45 to -25 mV), exocytosis from the RRP occurred in two phases. After the release of 20% or more of the RRP, the rate-constant of exocytosis fell by a factor of 4-10. Thus, synaptic depression was caused by a reduced sensitivity to Ca2+ influx, as well as simple depletion of the RRP. In the resting state, the rate of exocytosis varied with the amplitude of the Ca2+ current raised to the power of 2. In the depressed state, the sensitivity to Ca2+ influx was reduced approximately fourfold. The initial phase of exocytosis accelerated e-fold for every 2.1 mV depolarization over the physiological range and averaged 120 sec(-1) at -25 mV.The synapse of depolarizing bipolar cells therefore responds to a step depolarization in a manner similar to a high-pass filter. This transformation appears to be determined by the presence of rapidly releasable vesicles with differing sensitivities to Ca2+ influx. This might occur if vesicles were docked to the plasma membrane at different distances from Ca2+ channels. These results suggest that the ribbon synapse of depolarizing bipolar cells may be a site of adaptation in the retina.