Institute of Developmental Biology and Neurobiology, Johannes Gutenberg University Mainz, 55128 Mainz, Germany.
Institute for Biology/Genetics, Freie Universität Berlin, 14195 Berlin, Germany.
Proc Natl Acad Sci U S A. 2021 Jul 13;118(28). doi: 10.1073/pnas.2106621118.
Synaptic vesicle (SV) release, recycling, and plastic changes of release probability co-occur side by side within nerve terminals and rely on local Ca signals with different temporal and spatial profiles. The mechanisms that guarantee separate regulation of these vital presynaptic functions during action potential (AP)-triggered presynaptic Ca entry remain unclear. Combining genetics with electrophysiology and imaging reveals the localization of two different voltage-gated calcium channels at the presynaptic terminals of glutamatergic neuromuscular synapses (the Ca2 homolog, Dmca1A or cacophony, and the Ca1 homolog, Dmca1D) but with spatial and functional separation. Ca2 within active zones is required for AP-triggered neurotransmitter release. By contrast, Ca1 localizes predominantly around active zones and contributes substantially to AP-evoked Ca influx but has a small impact on release. Instead, L-type calcium currents through Ca1 fine-tune short-term plasticity and facilitate SV recycling. Separate control of SV exo- and endocytosis by AP-triggered presynaptic Ca influx through different channels demands efficient measures to protect the neurotransmitter release machinery against Ca1-mediated Ca influx. We show that the plasma membrane Ca ATPase (PMCA) resides in between active zones and isolates Ca2-triggered release from Ca1-mediated dynamic regulation of recycling and short-term plasticity, two processes which Ca2 may also contribute to. As L-type Ca1 channels also localize next to PQ-type Ca2 channels within axon terminals of some central mammalian synapses, we propose that Ca2, Ca1, and PMCA act as a conserved functional triad that enables separate control of SV release and recycling rates in presynaptic terminals.
突触囊泡 (SV) 释放、再循环和释放概率的塑性变化在神经末梢中同时发生，依赖于具有不同时间和空间特征的局部 Ca 信号。在动作电位 (AP) 触发的突触前 Ca 内流期间，保证这些重要的突触前功能分开调节的机制尚不清楚。结合遗传学、电生理学和成像揭示了两种不同的电压门控钙通道在谷氨酸能神经肌肉突触的突触前末梢的定位（Ca2 同源物，Dmca1A 或 cacophony，和 Ca1 同源物，Dmca1D），但具有空间和功能上的分离。活性区的 Ca2 是触发 AP 释放神经递质所必需的。相比之下，Ca1 主要定位于活性区周围，对 AP 诱发的 Ca 内流有很大贡献，但对释放的影响较小。相反，通过 Ca1 的 L 型钙电流微调短期可塑性并促进 SV 再循环。通过不同的通道触发的 AP 传入突触前 Ca 内流对 SV 出胞和内吞作用的单独控制需要有效的措施来保护神经递质释放机制免受 Ca1 介导的 Ca 内流的影响。我们表明，质膜 Ca ATP 酶（PMCA）位于活性区之间，将 Ca2 触发的释放与 Ca1 介导的再循环和短期可塑性的动态调节隔离开来，Ca2 可能也有助于这两个过程。由于 L 型 Ca1 通道也定位于某些哺乳动物中枢突触轴突末梢的 PQ 型 Ca2 通道旁边，我们提出 Ca2、Ca1 和 PMCA 作为一个保守的功能三联体起作用，使突触前末梢的 SV 释放和再循环速率的单独控制成为可能。
