Girod R, Popov S, Alder J, Zheng J Q, Lohof A, Poo M M
Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
J Neurosci. 1995 Apr;15(4):2826-38. doi: 10.1523/JNEUROSCI.15-04-02826.1995.
When exogenous ACh is loaded into the cytoplasm of cultured amphibian myocytes and fibroblasts, the cells undergo spontaneous quantal ACh secretion, as detected by the appearance of pulsatile membrane currents in Xenopus myocytes which are manipulated into contact with the cells. These currents resemble in many ways the miniature endplate currents (MEPCs) observed at developing neuromuscular synapses formed on these Xenopus myocytes. Analyses of the frequency, amplitude, and time course of these currents suggests similarity in the cellular mechanisms involved in the packaging and secretion of ACh quanta in fibroblasts, myocytes, and developing neurons. The size of the ACh packets released by the non-neuronal cells were found to be very similar to the size of the neuronal ACh quanta, which are thought to result from the exocytotic release of synaptic vesicles. Moreover, the kinetics with which the ACh packets are discharged from all three cell types are comparable, although the speed of secretion in non-neuronal cells is somewhat slower and more irregular. The spontaneous quantal ACh secretion from neurons and myocytes was decreased by reducing cytosolic Ca2+ level and enhanced by activation of protein kinase C with phorbol ester, but secretion from fibroblasts was unaffected by both treatments. The spontaneous secretion from fibroblasts did show some sensitivity to a rise in cytosolic Ca2+ after treatment with a Ca2+ ionophore. These observations support the hypothesis that the basic machinery for transmitter secretion operating in neurons derive from a more ubiquitous mechanism used for constitutive secretion and membrane trafficking in non-neuronal cells, and neuronal differentiation involves expression of additional unique components for the regulation of the spontaneous quantal secretion.
当将外源性乙酰胆碱（ACh）导入培养的两栖类肌细胞和成纤维细胞的细胞质中时，细胞会发生自发性量子化ACh分泌，这可通过与这些细胞接触的非洲爪蟾肌细胞中出现的搏动性膜电流检测到。这些电流在许多方面类似于在这些非洲爪蟾肌细胞上形成的发育中的神经肌肉突触处观察到的微小终板电流（MEPCs）。对这些电流的频率、幅度和时间进程的分析表明，在成纤维细胞、肌细胞和发育中的神经元中，ACh量子的包装和分泌所涉及的细胞机制具有相似性。发现非神经元细胞释放的ACh包的大小与神经元ACh量子的大小非常相似，后者被认为是由突触小泡的胞吐释放产生的。此外，尽管非神经元细胞中的分泌速度稍慢且更不规则，但从所有三种细胞类型中排出ACh包的动力学是可比的。通过降低细胞质Ca2+水平可减少神经元和肌细胞的自发性量子化ACh分泌，而用佛波酯激活蛋白激酶C可增强这种分泌，但两种处理对成纤维细胞的分泌均无影响。在用Ca2+离子载体处理后，成纤维细胞的自发性分泌确实对细胞质Ca2+的升高表现出一定的敏感性。这些观察结果支持这样一种假说，即神经元中用于递质分泌的基本机制源自非神经元细胞中用于组成型分泌和膜运输的更普遍的机制。并且神经元分化涉及表达额外的独特成分以调节自发性量子化分泌。
