Institute of Cell Biology, Beijing Normal University, Beijing 100875, China.
Cell Mol Neurobiol. 2011 Nov;31(8):1151-62. doi: 10.1007/s10571-011-9716-z. Epub 2011 Jun 9.
Toosendanin, a triterpenoid from Melia toosendan Sieb et Zucc, has been found before to be an effective anti-botulism agent, with a bi-phasic effect at both motor nerve endings and central synapse: an initial facilitation followed by prolonged depression. Initial facilitation may be due to activation of voltage-dependent calcium channels plus inhibition of potassium channels, but the depression is not fully understood. Toosendanin has no effect on intracellular calcium or secretion in the non-excitable pancreatic acinar cells, ruling out general toosendanin inhibition of exocytosis. In this study, toosendanin effects on sensory neurons isolated from rat nodose ganglia were investigated. It was found that toosendanin stimulated increases in cytosolic calcium and neuronal exocytosis dose dependently. Experiments with membrane potential indicator bis-(1,3-dibutylbarbituric acid)trimethine oxonol found that toosendanin hyperpolarized capsaicin-insensitive but depolarized capsaicin-sensitive neurons; high potassium-induced calcium increase was much smaller in hyperpolarizing neurons than in depolarizing neurons, whereas no difference was found for potassium-induced depolarization in these two types of neurons. In neurons showing spontaneous calcium oscillations, toosendanin increased the oscillatory amplitude but not frequency. Toosendanin-induced calcium increase was decreased in calcium-free buffer, by nifedipine, and by transient receptor potential vanilloid 1 (TRPV1) antagonist capsazepine. Simultaneous measurements of cytosolic and endoplasmic reticulum (ER) calcium showed an increase in cytosolic but a decrease in ER calcium, indicating that toosendanin triggered ER calcium release. These data together indicate that toosendanin modulates sensory neurons, but had opposite effects on membrane potential depending on the presence or absence of capsaicin receptor/TRPV 1 channel.
川楝素是从川楝树（Melia toosendan Sieb et Zucc）中提取的一种三萜类化合物，先前被发现是一种有效的抗肉毒杆菌毒素的药物，对运动神经末梢和中枢突触有双相作用：最初的兴奋，随后是长期的抑制。最初的兴奋可能是由于电压依赖性钙通道的激活和钾通道的抑制，但这种抑制的机制尚未完全清楚。川楝素对非兴奋胰腺腺泡细胞中的细胞内钙或分泌没有影响，排除了川楝素对胞吐作用的普遍抑制作用。在这项研究中，研究了川楝素对从大鼠结状神经节分离的感觉神经元的影响。结果发现，川楝素刺激细胞内钙增加和神经元胞吐作用呈剂量依赖性。使用膜电位指示剂双（1,3-二丁基巴比妥酸）三甲氧烷发现，川楝素超极化辣椒素不敏感但去极化辣椒素敏感神经元；高钾诱导的钙增加在超极化神经元中比在去极化神经元中要小得多，而这两种类型的神经元中，钾诱导的去极化没有差异。在显示自发性钙振荡的神经元中，川楝素增加了振荡幅度，但不改变频率。川楝素诱导的钙增加在无钙缓冲液中、硝苯地平中和辣椒素受体/瞬时受体电位香草酸 1（TRPV1）拮抗剂辣椒素中减少。同时测量细胞质和内质网（ER）钙显示细胞质钙增加，内质网钙减少，表明川楝素触发内质网钙释放。这些数据表明，川楝素调节感觉神经元，但对膜电位的影响取决于辣椒素受体/TRPV1 通道的存在与否。
