Inhibition of rapid delayed rectifier potassium current (IKr) by ischemia/reperfusion and its recovery by vitamin E in ventricular myocytes
Ischemia/reperfusion (I/R) induces prolongation of QT interval and action potential duration (APD), which is a major cardiac electrical disorder in patients with arrhythmias. However, the mechanism of QT interval prolongation induced by I/R remains unclear. In the present study, we hypothesized that the rapid component of delayed rectifier potassium ( I Kr ) channel plays an important role in I/R-induced QT interval prolongation. We observed a marked attenuation of I Kr and a significant prolongation of action potential duration (APD) in a simulated I/R system with sodium dithionite (Na 2 S 2 O 4 ) in ventricular myocytes of guinea pigs. The I Kr current density was inhibited by 64% and APD increased by 87% respectively. Moreover, the inhibition of I Kr is primarily ascribed to overproduction of reactive oxygen species (ROS) by I/R, which can be partly reversed by antioxidant vitamin E (100 μmol/L). The value of I Kr tail current density increased from 0.516 ± 0.040 pA/pF in I/R to 0.939 ± 0.091 pA/pF when treated with vitamin E. Moreover, we also demonstrated that QTc interval was increased by I/R and reversed by Vitamin E in isolated guinea pig hearts. In conclusion, the inhibition of I Kr is one of the underlying mechanisms of prolongation of QT interval and APD in I/R. Vitamin E might have a benefit in coronary reperfusion therapy .
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