Erecińska M, Dagani F, Nelson D, Deas J, Silver I A
Department of Pharmacology, University of Pennsylvania, Philadelphia 19104.
J Neurosci. 1991 Aug;11(8):2410-21. doi: 10.1523/JNEUROSCI.11-08-02410.1991.
Treatment of rat brain synaptosomes with 10 microM monensin stimulated activity of the Na/K pump, which enhanced oxygen consumption and lactate production. Glycolytic flux was also increased independently of the pump activation by a fall in [H+]i. Under such conditions, glycolysis provided 26% of ATP for the ouabain-sensitive ATPase, a value substantially greater than the 4% obtained in veratridine-treated preparations (Erecińska and Dagani, 1990). In C6 glioma cells, a glia-derived line endowed with high rates of aerobic lactate synthesis, the cytosolic and mitochondrial ATP generation contributed 50% each for the support of the pump in the presence of 10 microM monensin. The fraction of energy utilized by the pump was greater in synaptosomes than in C6 cells. Enhancement of ion movements was accompanied by changes in the levels of high-energy phosphate compounds. Measurements with ion-sensitive microelectrodes in C6 cells and cultured neurons showed that monensin caused an increase in pHi by 0.4-0.5 unit and a parallel rise in [Na+]i. The increases in [Na+]i were about twofold in both types of cells, but the absolute values attained were much higher in neurons (40-50 mM) than in C6 cells (10-12 mM). Membrane potentials transiently declined by less than 10 mV and returned to their original values after 20 min of treatment. Rises in [Ca2+]i were small in neurons as well as in C6 cells. These changes could be explained by the known mechanism and/or consequences of monensin action. In contrast, in synaptosomes monensin caused an internal alkalinization of 0.1-0.15 pH unit, a large depolarization of the plasma membrane, and massive leakage of potassium into the external medium. The decrease in plasma membrane potential was accompanied by an increase in [Ca/+]i and release of the neurotransmitter amino acids GABA, aspartate, and glutamate. The depolarization and loss of K+ were unaffected by calcium withdrawal, replacement of chloride with gluconate, and addition of 1 mM 4-acetamido-4'-isothiocyanostilebene-2,2'-disulfonic acid (SITS), but was markedly attenuated by elimination of Na+. It is proposed that in synaptosomes monensin and/or the consequences of its action open a nonspecific cation channel that allows Na+ entry and K+ exit, with a consequent decrease in membrane potential.
用10微摩尔莫能菌素处理大鼠脑突触体，可刺激钠钾泵的活性，增强氧消耗和乳酸生成。糖酵解通量也因细胞内氢离子浓度降低而独立于泵的激活增加。在这种情况下，糖酵解为哇巴因敏感的ATP酶提供了26%的ATP，这一数值显著高于用藜芦碱处理的制剂中获得的4%（埃雷辛斯卡和达加尼，1990年）。在C6胶质瘤细胞中，这是一种具有高有氧乳酸合成率的神经胶质来源细胞系，在存在10微摩尔莫能菌素的情况下，胞质和线粒体产生的ATP各为钠钾泵的维持贡献了50%。钠钾泵利用的能量比例在突触体中比在C6细胞中更大。离子运动的增强伴随着高能磷酸化合物水平的变化。用离子敏感微电极对C6细胞和培养的神经元进行测量表明，莫能菌素使细胞内pH值升高0.4 - 0.5个单位，同时细胞内钠离子浓度平行升高。两种细胞类型中细胞内钠离子浓度的升高约为两倍，但神经元中达到的绝对值（40 - 50毫摩尔）远高于C6细胞（10 - 12毫摩尔）。膜电位短暂下降不到10毫伏，并在处理20分钟后恢复到原始值。神经元和C6细胞中细胞内钙离子浓度的升高都很小。这些变化可以用莫能菌素作用的已知机制和/或后果来解释。相反，在突触体中，莫能菌素导致细胞内碱化0.1 - 0.15个pH单位，质膜大幅去极化，钾大量泄漏到细胞外介质中。质膜电位的降低伴随着细胞内钙离子浓度的增加以及神经递质氨基酸γ-氨基丁酸、天冬氨酸和谷氨酸的释放。去极化和钾离子的流失不受去除钙离子、用葡萄糖酸盐替代氯离子以及添加1毫摩尔4-乙酰氨基-4'-异硫氰基芪-2,2'-二磺酸（SITS）的影响，但通过去除钠离子可明显减弱。有人提出，在突触体中，莫能菌素和/或其作用的后果打开了一个非特异性阳离子通道，允许钠离子进入和钾离子流出，从而导致膜电位降低。
