Cerbai E, Ambrosio G, Porciatti F, Chiariello M, Giotti A, Mugelli A
Institute of Pharmacology, University of Ferrara, Italy.
Circulation. 1991 Oct;84(4):1773-82. doi: 10.1161/01.cir.84.4.1773.
Oxygen radicals have been implicated in the pathogenesis of reperfusion arrhythmias. However, the basic electrophysiological alterations accompanying the effects of oxygen radicals on action potential (AP) are poorly understood.
We investigated the effects of oxygen radicals generated by dihydroxyfumarate (DHF, 5 mM) on AP parameters and on ionic currents in patch-clamped guinea pig ventricular myocytes. DHF consistently caused a marked prolongation of AP duration, which was already significant after 60 seconds of exposure and continued to increase over time. Within 5 minutes, the majority of cells developed early afterdepolarizations (EADs) or became unexcitable. Both AP prolongation and occurrence of EADs were completely prevented in the presence of the oxygen radical scavengers superoxide dismutase (SOD) and catalase (CAT). Prolongation of AP duration was accompanied by a marked decreased in time-dependent potassium current (IK) and calcium current (ICa). The inward rectifier K current (IK1) was unaffected, suggesting no widespread changes in membrane properties. IK and ICa alterations were also significantly reduced by SOD and CAT. In additional experiments, intracellular calcium levels were kept constantly low by addition of 200 microM ethyleneglycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetra-acetic acid (EGTA) to the pipette solution. Under these conditions, the effects of DHF on AP duration and the occurrence of EADs were largely prevented. However, EGTA did not prevent cells from becoming unexcitable, nor did it affect the decrease in both IK and ICa upon exposure to DHF.
Exposure to an exogenous source of oxygen radicals may induce major electrophysiological alterations in isolated myocytes, which might be related to changes in specific ionic currents and in level of intracellular calcium. These alterations occur with a time course consistent with the rapid onset of ventricular arrhythmias in reperfused hearts.
氧自由基与再灌注性心律失常的发病机制有关。然而，氧自由基对动作电位（AP）影响所伴随的基本电生理改变却知之甚少。
我们研究了二羟基富马酸（DHF，5 mM）产生的氧自由基对豚鼠心室肌细胞动作电位参数和离子电流的影响。DHF持续导致动作电位时程显著延长，暴露60秒后即已显著，并随时间持续增加。5分钟内，大多数细胞出现早期后去极化（EADs）或变得难以兴奋。在存在氧自由基清除剂超氧化物歧化酶（SOD）和过氧化氢酶（CAT）的情况下，动作电位延长和EADs的发生均被完全阻止。动作电位时程的延长伴随着时间依赖性钾电流（IK）和钙电流（ICa）的显著降低。内向整流钾电流（IK1）未受影响，表明膜特性无广泛改变。SOD和CAT也显著减少了IK和ICa的改变。在额外的实验中，通过向微电极溶液中添加200 microM乙二醇双（β-氨基乙基醚）-N，N，N'，N'-四乙酸（EGTA）使细胞内钙水平持续保持在低水平。在这些条件下，DHF对动作电位时程和EADs发生的影响在很大程度上被阻止。然而，EGTA并未阻止细胞变得难以兴奋，也未影响暴露于DHF时IK和ICa的降低。
暴露于外源性氧自由基可能在分离的心肌细胞中诱导主要的电生理改变，这可能与特定离子电流的变化以及细胞内钙水平有关。这些改变的时间进程与再灌注心脏中室性心律失常的快速发作一致。
