Zamponi G W, French R J
Department of Medical Physiology, University of Calgary, Alberta, Canada.
Biophys J. 1993 Dec;65(6):2335-47. doi: 10.1016/S0006-3495(93)81292-X.
We have investigated block of sodium channels by diethylamide and phenol, which resemble the hydrophilic tertiary amine head and the hydrophobic aromatic tail of the lidocaine molecule, respectively. Diethylamide and phenol separately mimicked the fast and slow modes of block caused by lidocaine. Experiments were performed using single batrachotoxin-activated bovine cardiac and rat skeletal muscle sodium channels incorporated into neutral planar lipid bilayers. Diethylamide, only from the intracellular side, caused a voltage-dependent reduction in apparent single channel amplitude ('fast' block). Block was similar for cardiac and skeletal muscle channels, and increased in potency when extracellular sodium was replaced by N-methylglucamine, consistent with an intrapore blocking site. Thus, although occurring at 15-fold higher concentrations, block by diethylamide closely resembles the fast mode of block by lidocaine (Zamponi, G. W., D. D. Doyle, and R. J. French. 1993. Biophys. J. 65:80-90). For cardiac sodium channels, phenol bound to a closed state causing the appearance of long blocked events whose duration increased with phenol concentration. This slow block depended neither on voltage nor on the side of application, and disappeared upon treatment of the channel with trypsin. For skeletal muscle channels, slow phenol block occurred with only very low probability. Thus, phenol block resembles the slow mode of block observed for lidocaine (Zamponi, G. W., D. D. Doyle, and R. J. French. 1993. Biophys. J. 65:91-100). Our data suggest that there are separate sites for fast lidocaine block of the open channel and slow block of the "inactivated" channel. Fast block by diethylamide inhibited the long, spontaneous, trypsin-sensitive (inactivation-like) closures of cardiac channels, and hence secondarily antagonized slow block by phenol or lidocaine. This antagonism would potentiate shifts in the balance between the two modes of action of a tertiary amine drug caused by changes in the relative concentrations of the charged (fast blocking) and neutral (slow blocking) forms of the drug.
我们研究了二乙胺和苯酚对钠通道的阻断作用，它们分别类似于利多卡因分子的亲水性叔胺头部和疏水性芳香尾部。二乙胺和苯酚分别模拟了利多卡因引起的快速和慢速阻断模式。实验使用了掺入中性平面脂质双层的单蟾毒素激活的牛心脏和大鼠骨骼肌钠通道。仅从细胞内侧加入二乙胺会导致表观单通道振幅出现电压依赖性降低（“快速”阻断）。心脏和骨骼肌通道的阻断情况相似，当细胞外钠被N - 甲基葡糖胺取代时，阻断效力增强，这与孔内阻断位点一致。因此，尽管二乙胺的阻断浓度比利多卡因高15倍，但它与利多卡因的快速阻断模式非常相似（赞波尼，G.W.，D.D.多伊尔，和R.J.弗伦奇。1993年。《生物物理学杂志》65:80 - 90）。对于心脏钠通道，苯酚与关闭状态结合，导致出现长时间的阻断事件，其持续时间随苯酚浓度增加。这种慢速阻断既不依赖于电压也不依赖于应用的一侧，并且在用胰蛋白酶处理通道后消失。对于骨骼肌通道，苯酚的慢速阻断发生概率极低。因此，苯酚阻断类似于利多卡因观察到的慢速阻断模式（赞波尼，G.W.，D.D.多伊尔，和R.J.弗伦奇。1993年。《生物物理学杂志》65:91 - 100）。我们的数据表明，开放通道的利多卡因快速阻断和“失活”通道的慢速阻断存在不同的位点。二乙胺的快速阻断抑制了心脏通道长时间的、自发的、对胰蛋白酶敏感（类似失活）的关闭，因此继而拮抗了苯酚或利多卡因的慢速阻断。这种拮抗作用会增强由叔胺药物带电（快速阻断）和中性（慢速阻断）形式的相对浓度变化引起的两种作用模式之间平衡的转变。
