Huang J M, Tanguy J, Yeh J Z
Department of Pharmacology, Northwestern University Medical School, Chicago, Illinois 60611.
Biophys J. 1987 Aug;52(2):155-63. doi: 10.1016/S0006-3495(87)83203-4.
Modification of sodium channels by chloramine-T was examined in voltage clamped internally perfused crayfish and squid giant axons using the double sucrose gap and axial wire technique, respectively. Freshly prepared chloramine-T solution exerted two major actions on sodium channels: (a) an irreversible removal of the fast Na inactivation, and (b) a reversible block of the Na current. Both effects were observed when chloramine-T was applied internally or externally (5-10 mM) to axons. The first effect was studied in crayfish axons. We found that the removal of the fast Na inactivation did not depend on the states of the channel since the channel could be modified by chloramine-T at holding potential (from -80 to -100 mV) or at depolarized potential of -30 mV. After removal of fast Na inactivation, the slow inactivation mechanism was still present, and more channels could undergo slow inactivation. This result indicates that in crayfish axons the transition through the fast inactivated state is not a prerequisite for the slow inactivation to occur. During chloramine-T treatment, a distinct blocking phase occurred, which recovered upon washing out the drug. This second effect of chloramine-T was studied in detail in squid axons. After 24 h, chloramine-T solution lost its ability to remove fast inactivation but retained its blocking action. After removal of the fast Na inactivation, both fresh and aged chloramine-T solutions blocked the Na currents with a similar potency and in a voltage-dependent manner, being more pronounced at lower depolarizing potentials. A similar voltage-dependent block was observed with aged chloramine-T solution in an axon with intact inactivation. In contrast to the action of the fresh solution, the aged chloramine-T solution was found to accelerate the decay of Na currents.These results suggest that chloramine-T solution contains at least two active molecular forms that act at different sites in the Na channel.
分别使用双蔗糖间隙和轴向丝技术，在电压钳制的内部灌注小龙虾和鱿鱼巨轴突中研究了氯胺-T对钠通道的修饰作用。新制备的氯胺-T溶液对钠通道有两种主要作用：(a) 不可逆地消除快速钠失活，(b) 可逆地阻断钠电流。当将氯胺-T以5-10 mM的浓度内部或外部施加到轴突上时，两种效应均被观察到。第一种效应在小龙虾轴突中进行了研究。我们发现，快速钠失活的消除不依赖于通道状态，因为在保持电位（从-80到-100 mV）或-30 mV的去极化电位下，通道都可以被氯胺-T修饰。在消除快速钠失活后，慢失活机制仍然存在，并且更多的通道可以经历慢失活。这一结果表明，在小龙虾轴突中，通过快速失活状态的转变不是慢失活发生的先决条件。在氯胺-T处理期间，出现了一个明显的阻断阶段，在洗脱药物后恢复。氯胺-T的第二种效应在鱿鱼轴突中进行了详细研究。24小时后，氯胺-T溶液失去了消除快速失活的能力，但保留了其阻断作用。在消除快速钠失活后，新鲜和老化的氯胺-T溶液均以相似的效力和电压依赖性方式阻断钠电流，在较低的去极化电位下更为明显。在具有完整失活的轴突中，老化的氯胺-T溶液也观察到类似的电压依赖性阻断。与新鲜溶液的作用相反，发现老化的氯胺-T溶液加速了钠电流的衰减。这些结果表明，氯胺-T溶液至少包含两种活性分子形式，它们作用于钠通道的不同位点。
