Beresewicz A, Horackova M
Department of Physiology and Biophysics, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada.
J Mol Cell Cardiol. 1991 Aug;23(8):899-918. doi: 10.1016/0022-2828(91)90133-7.
The development of H2O2-induced changes in membrane potentials, membrane currents and corresponding contractile activity (shortening) were studied in rat and guinea-pig ventricular myocytes using the suction-pipette whole-cell clamp method. The cells exhibited a different sensitivity to 30 microM H2O2 in terms of time development of the changes, which were fully irreversible. The observed changes are described in three phases: (1) prolongation of action potential duration (APD) accompanied by increased contractility. With a prolonged exposure, the increased APD was accompanied by early afterdepolarizations (EADs), delayed afterdepolarizations (DADs) and aftercontractions. The changes in APD and the EADs were fully and permanently abolished by tetrodotoxin (TTX) but not by nifedipine, while the DADs and aftercontractions were abolished by ryanodine. These changes preceded phase (2), which was characterized by APD shortening, a decrease in contractility, membrane depolarization, single or multiple extrasystoles, or steady spontaneous activity; this phase could not be prevented by any of the above pharmacological interventions and resulted in a final phase (3) characterized by full depolarization and inexcitability. All the above changes were prevented by intracellular application of iron chelator-deferoxamine, indicating that .OH generated intracellularly in the presence of Fe3+ induces the observed changes. The examination of membrane currents indicated that the increased APD may be due to an increase in the TTX-sensitive Na+ current as well as to the decreased delayed current, while L-type Ca2+ channels appear to be unaffected. The shortening of APD during the second phase was associated with a large increase in the delayed K+ current. The increased contractility in the first stage appears to be due to increased sarcolemmal Ca2+ influx via Na(+)-Ca2+ exchange (among other possible mechanisms), leading to a loading of sarcoplasmic reticulum that eventually results in Ca2+ overload and functional failure.
采用吸液管全细胞钳制方法，研究了过氧化氢（H2O2）诱导大鼠和豚鼠心室肌细胞膜电位、膜电流及相应收缩活性（缩短）的变化。细胞对30微摩尔/升H2O2的变化时间发展表现出不同的敏感性，这些变化是完全不可逆的。观察到的变化分为三个阶段：（1）动作电位时程（APD）延长，伴有收缩力增加。随着暴露时间延长，APD延长伴有早期后去极化（EADs）、延迟后去极化（DADs）和后收缩。APD和EADs的变化可被河豚毒素（TTX）完全且永久消除，但硝苯地平不能，而DADs和后收缩可被ryanodine消除。这些变化先于阶段（2），其特征为APD缩短、收缩力降低、膜去极化、单个或多个期前收缩或稳定的自发活动；该阶段不能被上述任何一种药理干预阻止，并导致最终阶段（3），其特征为完全去极化和兴奋性丧失。细胞内应用铁螯合剂去铁胺可阻止上述所有变化，表明在Fe3+存在下细胞内产生的·OH诱导了观察到的变化。膜电流检测表明，APD增加可能是由于TTX敏感的Na+电流增加以及延迟电流降低，而L型Ca2+通道似乎未受影响。第二阶段APD缩短与延迟K+电流大幅增加有关。第一阶段收缩力增加似乎是由于通过Na(+)-Ca2+交换（以及其他可能机制）使肌膜Ca2+内流增加，导致肌浆网负荷增加，最终导致Ca2+过载和功能衰竭。
