The mechanism which enables activation of the nicotinic receptors to modify the synthesis of RNA was investigated in the incubated superior cervical ganglion of the rat. RNA labelling with [5-3H] uridine was used in order to screen the effects of varying the ionic environment and altering Na+ channels on the sequence of the three changes in ganglionic RNA synthesis induced by stimulation, i.e. a) an initial decrease, b) an increase during the late stages of stimulation, c) another increase taking place after the end of stimulation. These successive variations were obtained by either repetitive excitation of the preganglionic nerve, or application of ACh or carbachol to the ganglion. 2. The three changes in RNA synthesis mediated by ACh or carbachol were prevented when the KCl concentration of the medium was increased up to 37 mM or when NaCl of the medium was replaced with Tris or sucrose. This confirmed previous indications that the sequence of activity-induced changes is initiated by the transmembrane ionic fluxes mediated by nicotinic activation and not by depolarization per se. 3. Application of aconitine to resting ganglia for 1 h decreased the RNA synthesis to the same extent as a 1 h preganglionic or ACh stimulation. This effect was prevented by a concomitant application of tetrodotoxin (TTX) which also restored the ability of carbachol to modify RNA synthesis. This suggested that the initial decrease in RNA synthesis is caused by the increase in [Na+]i which seems to interfere directly with the transcription process. 4. The increase of RNA synthesis occurring during the late stages of synaptic activation was selectively inhibited by replacing Cl- of the medium with SO4-. On the other hand, the post-stimulation increase was selectively inhibited when the generation of after-hyperpolarization resulting from the electrogenic extrusion of Na+ was prevented by substituting LiCl for NaCl. This indicated that increases in RNA synthesis during and after the stimulation are triggered by different ionic events. 5. An induction of RNA synthesis was obtained, without previous activation of the nicotinic receptors, by incubating the ganglia at rest in conditions which entail the generation of an hyperpolarization resulting from the activation of the Na(+)-K- pump, i.e. low external KCl as well as application of TTX following an aconitine treatment. However, in these cases, the increase in RNA synthesis was delayed by about 2 h as compared to that observed after the end of nicotinic activation.(ABSTRACT TRUNCATED AT 400 WORDS)
摘要
在孵育的大鼠颈上神经节中，研究了使烟碱样受体激活从而改变RNA合成的机制。使用[5-³H]尿苷对RNA进行标记，以筛选改变离子环境和改变钠离子通道对刺激诱导的神经节RNA合成的三个变化顺序的影响，即：a）最初的减少；b）刺激后期的增加；c）刺激结束后发生的另一次增加。这些连续变化可通过对节前神经进行重复刺激，或向神经节施加乙酰胆碱（ACh）或卡巴胆碱来实现。2. 当培养基中氯化钾浓度增加到37 mM，或者培养基中的氯化钠被 Tris 或蔗糖替代时，由ACh或卡巴胆碱介导的RNA合成的三个变化被阻止。这证实了先前的迹象，即活性诱导变化的顺序是由烟碱样激活介导的跨膜离子通量引发的，而不是由去极化本身引发的。3. 向静息神经节施加乌头碱1小时，使RNA合成减少的程度与节前或ACh刺激1小时相同。同时施加河豚毒素（TTX）可阻止这种效应，TTX还恢复了卡巴胆碱改变RNA合成的能力。这表明RNA合成的最初减少是由细胞内钠离子浓度升高引起的，这似乎直接干扰了转录过程。4. 通过用硫酸根替代培养基中的氯离子，可选择性抑制突触激活后期发生的RNA合成增加。另一方面，当用氯化锂替代氯化钠阻止由钠离子电致外排导致的超极化后电位的产生时，刺激后RNA合成的增加被选择性抑制。这表明刺激期间和刺激后RNA合成的增加是由不同的离子事件触发的。5. 在静止条件下孵育神经节，通过激活钠钾泵产生超极化，即低细胞外氯化钾以及在乌头碱处理后施加TTX，可在未预先激活烟碱样受体的情况下诱导RNA合成。然而，在这些情况下，与烟碱样激活结束后观察到的情况相比，RNA合成的增加延迟了约2小时。（摘要截取自400字）
