Boyne A F, Bohan T P, Williams T H
J Cell Biol. 1974 Dec;63(3):780-95. doi: 10.1083/jcb.63.3.780.
Calcium (Ca)-containing fixation solutions applied to slices of electric organ of the electric ray, Narcine brasiliensis, have been shown to have three distinct ultrastructural effects on cholinergic synaptic vesicles of the nerve terminals. (a) An electron-dense particle (EDS) is observed within the vesicle; the particle is seen in unosmicated, unstained tissues and can be removed from thin sections by Ca-chelating agents. It is concluded that the EDS represents Ca bound by the vesicle. It is suggested that the bound ATP of the vesicle provides anionic Ca binding sites. (b) The vesicle membrane tends to 'crinkle' or collapse depending on the concentration of the other components of the fixative solution. The 'crinkling' or collapse are largely reversed by a wash step in the absence of Ca. (c) The presence of Ca results in the appearance of a population of vesicles which form characteristic fusions or 'tight' junctions with the terminal membrane. This appears to be morphological evidence for the proposal, which has been frequently put forward, that Ca facilitates such a fusion before discharge of vesicle-bound transmitter. With the discovery that the use of Ca-containing fixatives leads to the demonstration of a subpopulation of synaptic vesicles fused to the terminal membrane, we are led to propose that this is the ultrastructural location of the newly synthesized acetylcholine which has been shown by others to be preferentially released by stimulation.
已证实，将含钙（Ca）的固定液应用于巴西电鳐（Narcine brasiliensis）电器官切片时，会对神经末梢的胆碱能突触小泡产生三种不同的超微结构效应。（a）在小泡内观察到一个电子致密颗粒（EDS）；该颗粒在未经锇酸处理、未染色的组织中可见，并且可以通过钙螯合剂从薄片中去除。由此得出结论，EDS代表小泡结合的钙。有人提出，小泡结合的ATP提供了阴离子钙结合位点。（b）小泡膜倾向于“起皱”或塌陷，这取决于固定液中其他成分的浓度。在没有钙的情况下，通过洗涤步骤，“起皱”或塌陷在很大程度上会逆转。（c）钙的存在导致出现一群小泡，它们与终末膜形成特征性融合或“紧密”连接。这似乎是经常被提出的观点的形态学证据，即钙在小泡结合的递质释放之前促进这种融合。随着发现使用含钙固定剂会导致显示出与终末膜融合的突触小泡亚群，我们进而提出，这就是新合成的乙酰胆碱的超微结构位置，其他人已表明其在刺激时优先释放。
