Redox Reaction On The Persistent Sodium Current In Ventricular Myocytes, The Fast Sodium Current And Action Potential

Part IEffect of Hydrogen Peroxide on Persistent Sodium Current and Action Potential in Guinea Pig Ventricular MyocytesObjective: To study the effect of hydrogen peroxide (H₂O₂) on persistent sodium current (I_Nap) and action potential (AP) in guinea pig ventricular myocytes, and explore the possible mechanisms underlying them.Methods: The whole-cell, cell-attached and inside-out patch-clamp techniques were used to record I_NaP in isolated ventricular myocytes from guinea pig. The standard microelectrode techniques were used to record AP of the guinea pig papillary muscle cells.Results: (1) H₂O₂ (0.1, 0.5, and 1.0 mmol/L) increased the amplitude of whole cell I_NaP in concentration-dependent manner and reduced glutathione (GSH, 1 mmol/L) reversed the increased I_NaP. (2) H₂O₂ 1mmol/L increased persistent sodium channel activity in cell-attached and inside-out patches. The mean open probability was increased from control value 0.015±0.004 and 0.012±0.003 to 0.106±0.011 and 0.136±0.010, respectively (P<0.01 vs control). They were decreased to 0.039±0.024 and 0.027±0.006 after the application of GSH 1 mmol/L, respectively (P<0.01 vs H₂O₂). (3) The time when open probability began to increase (4.8±1.0 min vs 11.5±3.9 min, P<0.01) and reached maximum (9.6±1.6 min vs 18.7±4.7 min, P<0.01) was shorter in inside-out patches than that in cell-attached patches. (4) H₂O₂ 0.5 mmol/L had no significant effect on the resting potential (RP), but significantly prolonged the AP duration of repolarization to 50 % (APD₅₀), and to 90 % (APD₉₀), and decreased the amplitude of AP (APA), maximum upstroke velocity (V_max). These effects of H₂O₂ on AP were reversed after the application of GSH 1 mmol/L.Conclusion: H₂O₂ increased I_NaP of guinea pig ventricular myocytes in concentration-dependent manner, prolonged APD₅₀, APD₉₀ and decreased APA and Vmax of AP in guinea pig papillary muscle cells possibly by oxidating directly cell membrane sodium channel protein or the closely associated regulatory protein.Part IIEffect of Hypoxia on Persistent Sodium Current of Ventricular Myocytes from 3-week Infarcted Rat HeartObjective: To investigate the effect of hypoxia on persistent sodium current(INap) in single ventricular myocytes of acute myocardial infarction(AMI) heart of rats and study the mechanisms of cardiac arrhythmias that occur after AMI.Methods: AMI model was induced by ligating the left anterior descending coronary artery in rats. The whole-cell patch clamp techniqe was used to record the current in epicardial myocytes of infarcted region from rats at 3 week after AMI.Results: In normoxic conditions, the current density of INaP in cardiomyocytes of fake operation(FO) and AMI hearts was 0.144±0.022pA/pF(n=9), 0.121+0.013pA/pF(n=9, P<0.01) respectively, which could be blocked by tetrodotoxin(TTX). The amplitude of INaP was gradually increased with the prolongation of hypoxia time , but the increased extent of INaP in FO cells was significant bigger than that of AMI cells. The INaP could be blocked by lmmol/L glutathione.Conclusion: After AMI, the amplitude of INaP in infarcted and noninfarcted myocardium showed differences whether in normoxic or hypoxic conditions, which increased dispersion of repolarization. This could be one of the reasons of reentrant ventricular arrhythmias that occur after AMI.