Ridley John M, Milnes James T, Benest Andrew V, Masters Joe D, Witchel Harry J, Hancox Jules C
Department of Physiology and Cardiovascular Research Laboratories, School of Medical Sciences, University Walk, BS8 1TD, Bristol, UK
Biochem Biophys Res Commun. 2003 Jun 27;306(2):388-93. doi: 10.1016/s0006-291x(03)00980-x.
Class Ia antiarrhythmic drugs, including procainamide (PROC), are associated with cardiac sodium channel blockade, delayed ventricular repolarisation and with a risk of ventricular pro-arrhythmia. The HERG K(+) channel is frequently linked to drug-induced pro-arrhythmia. Therefore, in this study, interactions between PROC and HERG K(+) channels were investigated, with particular reference to potency and mechanism of drug action. Whole-cell patch-clamp recordings of HERG current (I(HERG)) were made at 37 degrees C from human embryonic kidney (HEK 293) cells stably expressing the HERG channel. Following activating pulses to +20 mV, I(HERG) tails were inhibited by PROC with an IC(50) value of approximately 139 microM. I(HERG) blockade was found to be both time- and voltage-dependent, demonstrating contingency upon HERG channel gating. However, I(HERG) inhibition by PROC was relieved by depolarisation to a highly positive membrane potential (+80 mV) that favoured HERG channel inactivation. These data suggest that PROC inhibits the HERG K(+) channel by a primarily 'open' or 'activated' channel state blocking mechanism and that avidity of drug-binding is decreased by extensive I(HERG) inactivation. The potency of I(HERG) blockade by PROC is much lower than for other Class Ia agents that have been studied previously under analogous conditions (quinidine and disopyramide), although the blocking mechanism appears similar. Thus, differences between the chemical structure of PROC and other Class Ia antiarrhythmic drugs may help provide insight into chemical determinants of blocking potency for agents that bind to open/activated HERG channels.
I类抗心律失常药物，包括普鲁卡因胺（PROC），与心脏钠通道阻滞、心室复极延迟以及心室心律失常风险相关。人乙醚相关基因（HERG）钾通道常与药物诱导的心律失常有关。因此，在本研究中，研究了PROC与HERG钾通道之间的相互作用，特别涉及药物作用的效力和机制。在37℃下，从稳定表达HERG通道的人胚肾（HEK 293）细胞进行HERG电流（I(HERG)）的全细胞膜片钳记录。在向+20 mV的激活脉冲后，I(HERG)尾电流被PROC抑制，半数抑制浓度（IC(50)）值约为139 μM。发现I(HERG)阻滞具有时间和电压依赖性，表明其取决于HERG通道门控。然而，通过去极化至高度正的膜电位（+80 mV）可缓解PROC对I(HERG)的抑制，这种去极化有利于HERG通道失活。这些数据表明，PROC通过主要的“开放”或“激活”通道状态阻断机制抑制HERG钾通道，并且广泛的I(HERG)失活会降低药物结合亲和力。与先前在类似条件下研究的其他I类药物（奎尼丁和丙吡胺）相比，PROC对I(HERG)的阻滞效力要低得多，尽管其阻断机制似乎相似。因此，PROC与其他I类抗心律失常药物化学结构的差异可能有助于深入了解与开放/激活的HERG通道结合的药物阻断效力的化学决定因素。
