Exocytosis, Mediatophore, and Vesicular Ca2+/H+ Antiport in Rapid Neurotransmission
Exocytosis, Mediatophore, and Vesicular Ca2+/H+ Antiport in Rapid Neurotransmission
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DOI：
10.1111/j.1749-6632.2008.04000.x
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发表时间：
2009-01-01
期刊：
影响因子：
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通讯作者：
Goncalves, Paula P.
中科院分区：
文献类型：
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作者：
Dunant, Yves;Cordeiro, J. Miguel;Goncalves, Paula P.
在快速突触中，神经递质量子在不到100 μ s的时间内发出，通常频率很高。使用突触的快速冷冻固定，我们发现一个非常短暂的（2-3毫秒）的变化影响突触前膜的膜内颗粒。囊泡开口也发生，但在一个显着的延迟。颗粒变化最可能与介体（一种220 kDa的蛋白脂质）有关。在突触前膜的活动区显示了介体细胞聚集体。在脂质体、非洲爪蟾卵母细胞和神经母细胞瘤细胞中重构，介体以Ca 2+依赖性和量子方式释放乙酰胆碱，模仿生理释放。在限制性突触前“纳米结构域”中，Ca 2+浓度爆炸性地达到高水平，然后以300-400 μ s的时间常数消失。在对Ca 2+缓冲的快相有贡献的过程中，囊泡Ca 2 +/H+反向转运起着主要作用。通过囊泡ATP酶依赖性质子梯度供能，反向转运对Ca 2+具有低亲和力。我们使用巴弗洛霉素A1灭活了Ca 2 +/H+反向转运，其消除了质子梯度。结果，突触后电位持续时间增加约3 ms，这是由持续释放递质引起的效应。通过将细胞外Ca 2+替换为抑制反向转运的锶，获得了类似的变化。因此，反向转运的功能是阻断突触前Ca ~（2+）信号，使递质释放时间缩短。这允许传输以高频率操作。在短暂的刺激后，钙在突触囊泡中短暂积累，在那里钙与递质交换。钙随后从末端清除，最可能是通过胞吐作用。
In rapid synapses, neurotransmitter quanta are emitted in less than 100 mu s, often at a high frequency. Using fast cryofixation of synapses, we found a very brief (2-3 ms) change affecting intramembrane particles in presynaptic membrane. Vesicle openings also occurred but after a significant delay. The particle change is most probably linked to mediatophore, a proteolipid of 220 kDa. Mediatophore aggregates were demonstrated in active zones of the presynaptic membrane. Reconstituted in liposomes, Xenopus oocytes, and neuroblastoma cells, mediatophore releases acetylcholine in a Ca2+-dependent and quantal manner, mimicking physiological release. In restricted presynaptic "nanodomains," Ca2+ concentration explosively reaches a high level and then vanishes with a time constant of 300-400 mu s. Among the processes contributing to the fast phase of Ca2+ buffering, a vesicular Ca2+/H+ antiport plays a major role. Energized by the Vesicular-ATPase-dependent proton gradient, the antiport has a low affinity for Ca2+. We inactivated the Ca2+/H+ antiport using bafilomycin A1, which annihilates the proton gradient. As a result, the postsynaptic potential was increased in duration for about 3 ms, an effect caused by persistence of transmitter release. A similar change was obtained by replacing extracellular Ca2+ by strontium, which inhibits the antiport. The antiport function, therefore, is to abbreviate the presynaptic Ca2+ Signal, making transmitter release briefer. This allows transmission to operate at high frequency. Following a brief period of stimulation, calcium transiently accumulates in synaptic vesicles where it is exchanged against transmitter. Calcium is subsequently cleared from the terminal, most probably by exocytosis.