Release from the cone ribbon synapse under bright light conditions can be controlled by the opening of only a few Ca2+ channels
Release from the cone ribbon synapse under bright light conditions can be controlled by the opening of only a few Ca2+ channels
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DOI：
10.1152/jn.00634.2011
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发表时间：
2011-12-01
影响因子：
2.5
通讯作者：
Thoreson, Wallace B.
中科院分区：
文献类型：
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作者：
Bartoletti, Theodore M.;Jackman, Skyler L.;Thoreson, Wallace B.
Bartoletti TM、Jackman SL、Babai N、Mercer AJ、Kramer RH、Thoreson WB。在强光条件下，锥体带状突触的释放可以通过仅打开几个 Ca2+ 通道来控制。 J Neurophysiol 106: 2922-2935, 2011。首次发表于 2011 年 8 月 31 日； doi: 10.1152/jn.00634.2011.-光使视锥细胞光感受器超极化，导致突触电压门控 Ca2+ 通道不频繁打开。为了了解这些条件下的神经传递，我们确定了锥带突触处囊泡融合所需的 L 型 Ca2+ 通道开口的数量。 Ca2+ 电流 (I-Ca) 在电压钳位视锥细胞中被激活，并从蝾螈视网膜切片制备中的水平细胞记录兴奋性突触后电流 (EPSC)。通过I-Ca的均值方差分析计算Ca2+通道数和单通道电流幅度。两种不同的比较——一种将释放事件的平均数量与平均 I-Ca 幅度进行比较，另一种涉及两个 EPSC 和同时记录的锥形 I-Ca 的反卷积——表明在刺激的最初几毫秒内，在释放峰值时每个囊泡的融合少于三个 Ca2+ 通道开口。打开较少的 Ca2+ 通道并不能提高融合效率，这表明在强去极化过程中很少发生不必要的通道打开。我们使用根据经验确定的突触尺寸、囊泡池大小、释放的 Ca2+ 依赖性、Ca2+ 通道数和 Ca2+ 通道特性来模拟锥体突触的释放。当添加屏障以减缓 Ca2+ 扩散时，该模型复制了观察结果。与扩散屏障的存在一致，用可扩散 Ca2+ 缓冲液透析锥体不会影响释放效率。 Ca2+ 通道的紧密聚集，以及高 Ca2+ 亲和力释放机制和扩散屏障，促进了 Ca2+ 流入和囊泡融合之间的线性耦合。当视锥细胞被强光超极化时，这可以改善对小光衰减的检测。
Bartoletti TM, Jackman SL, Babai N, Mercer AJ, Kramer RH, Thoreson WB. Release from the cone ribbon synapse under bright light conditions can be controlled by the opening of only a few Ca2+ channels. J Neurophysiol 106: 2922-2935, 2011. First published August 31, 2011; doi: 10.1152/jn.00634.2011.-Light hyperpolarizes cone photoreceptors, causing synaptic voltage-gated Ca2+ channels to open infrequently. To understand neurotransmission under these conditions, we determined the number of L-type Ca2+ channel openings necessary for vesicle fusion at the cone ribbon synapse. Ca2+ currents (I-Ca) were activated in voltage-clamped cones, and excitatory postsynaptic currents (EPSCs) were recorded from horizontal cells in the salamander retina slice preparation. Ca2+ channel number and single-channel current amplitude were calculated by mean-variance analysis of I-Ca. Two different comparisons-one comparing average numbers of release events to average I-Ca amplitude and the other involving deconvolution of both EPSCs and simultaneously recorded cone I-Ca-suggested that fewer than three Ca2+ channel openings accompanied fusion of each vesicle at the peak of release during the first few milliseconds of stimulation. Opening fewer Ca2+ channels did not enhance fusion efficiency, suggesting that few unnecessary channel openings occurred during strong depolarization. We simulated release at the cone synapse, using empirically determined synaptic dimensions, vesicle pool size, Ca2+ dependence of release, Ca2+ channel number, and Ca2+ channel properties. The model replicated observations when a barrier was added to slow Ca2+ diffusion. Consistent with the presence of a diffusion barrier, dialyzing cones with diffusible Ca2+ buffers did not affect release efficiency. The tight clustering of Ca2+ channels, along with a high-Ca2+ affinity release mechanism and diffusion barrier, promotes a linear coupling between Ca2+ influx and vesicle fusion. This may improve detection of small light decrements when cones are hyperpolarized by bright light.