Hansen G, Ulbricht W
Physiologisches Institut, Universität Kiel, Federal Republic of Germany.
Pflugers Arch. 1991 Dec;419(6):588-95. doi: 10.1007/BF00370300.
Voltage clamp experiments were done on single myelinated frog nerve fibres. The rate of block of Na+ channels by tetrodotoxin (TTX) was obtained from changes in peak Na+ current during 1-Hz trains of depolarizing impulses. In hypertonic Na(+)-rich solution (216 mM) the stationary block was reduced compared with Na(+)-poor solutions (54 mM or less; tetramethylammonium ions substituting for Na+). Washout in 216 mM Na+ was faster than in 54 mM Na+. Concentration of Na+ [( Na+]) little affected onset of block. After equilibration in Na(+)-poor TTX solution, a sudden application of Na(+)-rich toxin solution led to a partial relief from block that proceeded faster than the onset in the latter solution. Comparable results were obtained with saxitoxin (STX) and in analogous Li+ solutions. Most of the observed phenomena could be quantitatively fitted by a cyclic model in which cations favour the transition of channels (unblocked and blocked) from a high- to a low-affinity state from which toxin dissociates faster.
在单个有髓鞘的蛙神经纤维上进行了电压钳实验。通过在1赫兹去极化脉冲序列期间峰值钠电流的变化，获得了河豚毒素（TTX）对钠通道的阻断速率。与贫钠溶液（54 mM或更低；用四甲基铵离子替代钠）相比，在富含钠的高渗溶液（216 mM）中，稳态阻断减少。在216 mM钠溶液中的洗脱速度比在54 mM钠溶液中快。钠浓度[（Na+）]对阻断的起始影响很小。在贫钠TTX溶液中平衡后，突然施加富含钠的毒素溶液会导致部分阻断缓解，其进程比在后者溶液中的起始更快。用石房蛤毒素（STX）和类似的锂溶液也得到了类似的结果。大多数观察到的现象可以用一个循环模型进行定量拟合，在该模型中，阳离子有利于通道（未阻断和阻断）从高亲和力状态向低亲和力状态转变，从低亲和力状态中毒素解离得更快。
