Pinet Caroline, Le Grand Bruno, John Gareth W, Coulombe Alain
Centre Nationale de la Recherche Scientifique, Unité Mixte de Recherche 8078, Hôpital Marie Lannelongue, Le Plessis Robinson, France.
Circulation. 2002 Oct 15;106(16):2098-103. doi: 10.1161/01.cir.0000034510.64828.96.
Thrombin plays a role in mediating ischemic injury and cardiac arrhythmias, but the mechanisms involved are poorly understood. Because voltage-gated sodium channels (VGSCs) have not previously been considered, putative effects of thrombin on VGSC function were investigated in human isolated cardiomyocytes.
Sodium current (I(Na)) was recorded by the whole-cell patch-clamp method. Thrombin increased peak I(Na) amplitude in an activity-dependent manner, from 1 to 100 U/mL, with an apparent EC50 of 91+/-16 U/mL. When tested at 32 U/mL, thrombin-increased I(Na) was abolished by tetrodotoxin (50 micromol/L). Thrombin effects on I(Na) were reversible and repeatable, and 100 U/mL doubled peak I(Na) amplitude. Thrombin (32 U/mL) shifted I(Na) activation to hyperpolarized potentials without affecting steady-state inactivation, producing unusually large increases in window current. Hirudin (320 U/mL) or haloenol lactone suicide substrate (10 micromol/L) failed to significantly affect these effects of thrombin. In current-clamped cardiomyocytes, thrombin (32 U/mL) depolarized resting membrane potential by 10 mV.
Facilitation of VGSC activation causing large increases in window current is a major mechanism by which thrombin may promote ischemic sodium loading and injury.
凝血酶在介导缺血性损伤和心律失常中起作用，但其涉及的机制尚不清楚。由于此前未考虑电压门控钠通道（VGSCs），因此在人离体心肌细胞中研究了凝血酶对VGSC功能的假定作用。
采用全细胞膜片钳法记录钠电流（I(Na)）。凝血酶以活性依赖的方式增加I(Na)峰值幅度，范围为1至100 U/mL，表观半数有效浓度（EC50）为91±16 U/mL。当以32 U/mL进行测试时，凝血酶增加的I(Na)被河豚毒素（50 μmol/L）消除。凝血酶对I(Na)的作用是可逆且可重复的，100 U/mL可使I(Na)峰值幅度翻倍。凝血酶（32 U/mL）使I(Na)激活向超极化电位偏移，而不影响稳态失活，导致窗电流异常大幅增加。水蛭素（320 U/mL）或卤代烯醇内酯自杀底物（10 μmol/L）未能显著影响凝血酶的这些作用。在电流钳制的心肌细胞中，凝血酶（32 U/mL）使静息膜电位去极化10 mV。
促进VGSC激活导致窗电流大幅增加是凝血酶促进缺血性钠负荷和损伤的主要机制。
