Benoit E, Juzans P, Legrand A M, Molgo J
Laboratoire de Physiologie Cellulaire, E.R.S. C.N.R.S., Université de Paris Sud, Orsay, France.
Neuroscience. 1996 Apr;71(4):1121-31. doi: 10.1016/0306-4522(95)00506-4.
Ciguatoxin-1b, the major toxin involved in ciguatera fish poisoning, and D-mannitol were examined on frog nodes of Ranvier using confocal laser scanning microscopy and conventional current- and voltage-clamp techniques. During the action of 10 nM ciguatoxin-1b, an increase in nodal volume was observed as determined by digital image processing and three-dimensional reconstruction of axons. The increase was prevented by blocking Na+ channels with tetrodotoxin. Ciguatoxin-1b (10 nM) induced high frequency action potential discharges up to 70-100 Hz. Analysis of Na+ current revealed that the toxin modified a current fraction which was activated at resting membrane potential and failed to inactivate. Increasing the osmolality of the external solution by about 50% with D-mannitol restored the nodal volume to its control value and suppressed spontaneous action potentials. In addition, D-mannitol affected unmodified and ciguatoxin-1b-treated Na+ currents in a similar manner causing a reduction of maximum conductance, negative shifts of current reversal potential and modification of the voltage-dependence of current activation and inactivation. In conclusion, ciguatoxin-1b induced a tetrodotoxin-sensitive swelling of nodes of Ranvier and selectively affected the Na+ current of myelinated axons. It is proposed that ciguatoxin-1b, by modifying Na+ current, increased intracellular Na+ concentration which caused water influx and nodal swelling. This may explain some of the reported symptoms of ciguatera fish poisoning. D-mannitol, an agent used for ciguatera treatment, was found to reverse the effects of ciguatoxin-1b by reducing Na+ entry and increasing the efflux of water through its osmotic action. It is the first time that osmotic changes produced by the selective activation of ionic channels, i.e. Na+ channels, are reported.
利用共聚焦激光扫描显微镜以及传统的电流钳和电压钳技术，对雪卡毒素中毒的主要毒素西加毒素-1b和D-甘露醇在蛙类郎飞结上进行了研究。在10 nM西加毒素-1b作用期间，通过对轴突进行数字图像处理和三维重建确定，观察到结体积增加。用河豚毒素阻断钠通道可防止这种增加。西加毒素-1b（10 nM）诱导高达70 - 100 Hz的高频动作电位发放。对钠电流的分析表明，该毒素改变了一部分在静息膜电位时被激活且不能失活的电流。用D-甘露醇将外部溶液的渗透压提高约50%可使结体积恢复到对照值，并抑制自发动作电位。此外，D-甘露醇以类似方式影响未修饰和经西加毒素-1b处理的钠电流，导致最大电导降低、电流反转电位负移以及电流激活和失活的电压依赖性改变。总之，西加毒素-1b诱导了河豚毒素敏感的郎飞结肿胀，并选择性地影响有髓轴突的钠电流。有人提出，西加毒素-1b通过改变钠电流增加细胞内钠浓度，从而导致水流入和结肿胀。这可能解释了雪卡毒素中毒所报告的一些症状。发现用于治疗雪卡毒素中毒的药物D-甘露醇通过减少钠内流并通过其渗透作用增加水外流来逆转西加毒素-1b的作用。这是首次报道由离子通道（即钠通道）的选择性激活产生的渗透变化。
