Csillik B, Knyihár-Csillik E
Acta Biol Acad Sci Hung. 1980;31(1-3):49-56.
By means of electron cytochemical analysis of rat neuromuscular junctions subjected to perfusion with a calcium-containing (5 mM) aldehyde fixative, two kinds of presynaptic calcium binding sites were demonstrated. "A" sites are located above openings of junctional folds; these triangular elements are identical with presynaptic protrusions of the active zone and probably comprise calcium channels of the presynaptic membrane, "B" sites, located within the terminal axoplasm, are associated to multivesicular bodies probably accumulating surplus intracellular calcium. This fine structural arrangement enables a highly parsimonious usage of extracellular calcium in inducing release of acetylcholine from synaptic vesicles. Junctional folds of the postsynaptic membrane may funnel calcium ions exactly to spatially restricted calcium channels. Having entered the terminal through the channels opened by the arrival of nerve action potential, calcium ions may exert their action upon synaptic vesicles accumulated in the closest vicinity by means of stripping off hydration barriers and by inducing membrane fusions, that finally result in quantal release of acetylcholine from the terminal.
通过对用含钙（5 mM）醛固定剂灌注的大鼠神经肌肉接头进行电子细胞化学分析，发现了两种突触前钙结合位点。“A”位点位于突触褶皱开口上方；这些三角形结构与活性区的突触前突出物相同，可能构成突触前膜的钙通道。“B”位点位于轴突终质内，与多泡体相关，可能积累细胞内多余的钙。这种精细的结构安排使得在诱导突触小泡释放乙酰胆碱时能够高度节俭地利用细胞外钙。突触后膜的突触褶皱可能将钙离子精确地导向空间受限的钙通道。钙离子通过神经动作电位到达时打开的通道进入终末后，可通过去除水化屏障和诱导膜融合对最邻近积累的突触小泡发挥作用，最终导致乙酰胆碱从终末以量子方式释放。
