Suidan H S, Tolkovsky A M
Department of Biochemistry, University of Cambridge, United Kingdom.
J Neurosci. 1993 Mar;13(3):1190-201. doi: 10.1523/JNEUROSCI.13-03-01190.1993.
We have examined the question of how regenerating sympathetic neurons that are concomitantly induced to become cholinergic regulate choline allocation between ACh and the phospholipid synthetic pathway. The allocation of choline into ACh increased parabolically with time in culture, and by 3 weeks, cultures with neurites of approximately 6 mm length were incorporating over 85% of the choline locally in the neurites into four major metabolites: ACh, phosphorylcholine, cytidine diphosphocholine, and phosphatidylcholine. The near-equivalent distribution of labeled choline between intracellular choline, ACh, and phosphorylcholine was independent of time (5 min to 6 hr) and choline concentration (0.125-30 microM), phosphatidylcholine being the sole metabolite whose level in the neurites increased steadily with incubation time. Relative choline distribution into ACh and phosphorylcholine was unaltered even after a brief depolarizing prepulse, which caused a two- to fourfold enhancement in the total choline incorporated. These observations, allied with the similar half-saturation constants and Vmax values of CAT and choline kinase for intracellular choline, suggest that growing sympathetic neurons are poised to allocate choline symmetrically between the synthesis of ACh and phosphatidylcholine in the neurites. When, however, the supply of choline was limited either by replacement of Na+ in the medium with N-methyl-D-glucamine, or by vesamicol, a 90-97% reduction in intracellular choline caused a similar decline in ACh levels but synthesis of metabolites of the phosphatidylcholine pathway was maintained unperturbed, as if no drug was present. We suggest that this can be accounted for by a 10-fold increase in choline kinase activity. Thus, growing sympathetic neurons that express cholinergic properties not only maintain their chief cellular phosphatidylcholine-synthesizing activity concomitantly with ACh synthesis in the neurites, but may also preserve phosphatidylcholine synthesis more effectively than ACh synthesis when the supply of choline is perturbed. Relinquishing ACh synthesis during growth may be one way of conserving and encouraging neurite regeneration.
我们研究了一个问题，即同时被诱导成为胆碱能神经元的再生交感神经元如何调节胆碱在乙酰胆碱（ACh）和磷脂合成途径之间的分配。随着培养时间的推移，胆碱向ACh中的分配呈抛物线形增加，到3周时，具有约6毫米长神经突的培养物将神经突中超过85%的胆碱局部整合到四种主要代谢产物中：ACh、磷酸胆碱、胞苷二磷酸胆碱和磷脂酰胆碱。标记胆碱在细胞内胆碱、ACh和磷酸胆碱之间的近乎相等的分布与时间（5分钟至6小时）和胆碱浓度（0.125 - 30微摩尔）无关，磷脂酰胆碱是神经突中唯一其水平随孵育时间稳定增加的代谢产物。即使经过短暂的去极化预脉冲后，相对胆碱在ACh和磷酸胆碱中的分布也未改变，而短暂的去极化预脉冲使整合的总胆碱增加了两到四倍。这些观察结果，再加上胆碱乙酰转移酶（CAT）和胆碱激酶对细胞内胆碱的类似半饱和常数和最大反应速度（Vmax）值，表明正在生长的交感神经元准备好在神经突中ACh和磷脂酰胆碱的合成之间对称地分配胆碱。然而，当胆碱供应受到限制时，要么通过用N - 甲基 - D - 葡糖胺替代培养基中的Na +，要么通过vesamicol，细胞内胆碱减少90 - 97%会导致ACh水平出现类似下降，但磷脂酰胆碱途径的代谢产物合成保持不受干扰，就好像没有药物存在一样。我们认为这可以通过胆碱激酶活性增加10倍来解释。因此，表达胆碱能特性的正在生长的交感神经元不仅在神经突中与ACh合成同时维持其主要的细胞磷脂酰胆碱合成活性，而且当胆碱供应受到干扰时，可能比ACh合成更有效地保留磷脂酰胆碱合成。在生长过程中放弃ACh合成可能是保存和促进神经突再生的一种方式。
