Israël M, Dunant Y
Laboratoire de Neurobiologie Cellulaire et Moléculaire, C.N.R.S. F-91198 Gif-sur-Yvette, France.
Mol Neurobiol. 1998 Feb;16(1):1-20. doi: 10.1007/BF02740600.
Choline acetyltransferase and vesicular acetylcholine-transporter genes are adjacent and coregulated. They define a cholinergic locus that can be turned on under the control of several factors, including the neurotrophins and the cytokines. Hirschprung's disease, or congenital megacolon, is characterized by agenesis of intramural cholinergic ganglia in the colorectal region. It results from mutations of the RET (GDNF-activated) and the endothelin-receptor genes, causing a disregulation in the cholinergic locus. Using cultured cells, it was shown that the cholinergic locus and the proteins involved in acetylcholine (ACh) release can be expressed separately ACh release could be demonstrated by means of biochemical and electrophysiological assays even in noncholinergic cells following preloading with the transmitter. Some noncholinergic or even nonneuronal cell types were found to be capable of releasing ACh quanta. In contrast, other cells were incompetent for ACh release. Among them, neuroblastoma N18TG-2 cells were rendered release-competent by transfection with the mediatophore gene. Mediatophore is an ACh-translocating protein that has been purified from plasma membranes of Torpedo nerve terminal; it confers a specificity for ACh to the release process. The mediatophores are activated by Ca2+; but with a slower time course, they can be desensitized by Ca2+. A strictly regulated calcium microdomain controls the synchronized release of ACh quanta at the active zone. In addition to ACh and ATP, synaptic vesicles have an ATP-dependent Ca2+ uptake system; they transiently accumulate Ca2+ after a brief period of stimulation. Those vesicles that are docked close to Ca2+ channels are therefore in the best position to control the profile and dynamics of the Ca2+ microdomains. Thus, vesicles and their whole set of associated proteins (SNAREs and others) are essential for the regulation of the release mechanism in which the mediatophore seems to play a key role.
胆碱乙酰转移酶基因和囊泡乙酰胆碱转运体基因相邻且共同调控。它们定义了一个胆碱能基因座，该基因座可在包括神经营养因子和细胞因子在内的多种因素控制下被激活。先天性巨结肠，又称赫希施普龙病，其特征是结直肠区域壁内胆碱能神经节发育不全。它是由RET（胶质细胞源性神经营养因子激活）和内皮素受体基因突变引起的，导致胆碱能基因座失调。利用培养细胞研究发现，胆碱能基因座和参与乙酰胆碱（ACh）释放的蛋白质可以分别表达。即使在预先加载递质后的非胆碱能细胞中，也可通过生化和电生理检测证实ACh的释放。研究发现，一些非胆碱能甚至非神经元细胞类型能够释放ACh量子。相比之下，其他细胞则无法释放ACh。其中，神经母细胞瘤N18TG - 2细胞通过转染介导蛋白基因而具备释放能力。介导蛋白是一种从电鳐神经末梢质膜中纯化出来的ACh转运蛋白，它赋予ACh释放过程特异性。介导蛋白由Ca2 +激活，但时间进程较慢，且可被Ca2 +脱敏。一个严格调控的钙微区控制着ACh量子在活性区的同步释放。除了ACh和ATP外，突触囊泡还有一个ATP依赖的Ca2 +摄取系统；在短暂刺激后，它们会短暂积累Ca2 +。因此，那些停靠在Ca2 +通道附近的囊泡最适合控制钙微区的分布和动态变化。所以，囊泡及其整套相关蛋白（SNAREs等）对于释放机制的调节至关重要，而介导蛋白似乎在其中发挥着关键作用。
