Hydrogen peroxide accelerates ventricular arrhythmogenesis by inactivating N‐type calcium channels in cardiac vagal postganglionic neurons in type 2 diabetic rats

Abstract

Withdrawal of cardiac vagal activity is a common complication in patients with type 2 diabetes mellitus (T2DM), and is associated with arrhythmia-related sudden cardiac death and high mortality in T2DM patients. Although our recent study has demonstrated that reduction of N-type calcium (Cav2.2) currents and cell excitability of cardiac vagal postganglionic (CVP) neurons exacerbates myocardial infarction-evoked ventricular arrhythmias and mortality in T2DM rats, the mechanisms responsible for T2DM-reduced Cav2.2 channel activity in CVP neurons remain unclear. Since reactive oxygen species (ROS) has been reported to modulate calcium channel activity in peripheral postganglionic neurons, here we tested if hydrogen peroxide (H2O2, a type of ROS) overproduction inactivates Cav2.2 channels and further contributes to ventricular vagal dysfunction and ventricular arrhythmogenesis in T2DM. Rat T2DM was induced by a high-fat diet plus streptozotocin injection. Adenoviral catalase gene (Ad.CAT, 2 µl, 1 x 1010 pfu/ml) was microinjected into CVP neurons to scavenge local H2O2 production. Reduced catalase expression accompanied by overproduction of H2O2 was detected in the CVP neurons in T2DM rats. In vivo transfection of Ad.CAT not only increased protein expression of catalase but also attenuated H2O2 production in CVP neurons in T2DM rats. Data from reverse-phase protein array also demonstrated that overexpression of catalase by transfection of Ad.CAT into CVP neurons markedly increased T2DM-reduced protein expression of Cav2.2 in CVP neurons. Local microinjection of Ad.CAT into CVP neurons also significantly restored T2DM-blunted ventricular vagal activity, as demonstrated by an improvement in the response of left ventricular systolic pressure to left vagal efferent nerve stimulation. Additionally, in the power spectral analysis of heart rate variability (HRV), transfection of Ad.CAT into CVP neurons increased the T2DM-attenuated high frequency power (an index of vagal activity), leading to further restoration of the low frequency to high frequency ratio. Moreover, the inducibility of ventricular arrhythmia measured in anesthetized condition was significantly reduced in T2DM rats transfected with Ad.CAT, compared with T2DM rats (0.75±0.48 in T2DM+Ad.CAT group vs. 3.0±1.38 in T2DM group). Transfection of Ad. vector into CVP neurons had no effects on protein expression of catalase and Cav2.2, ventricular vagal activity, HRV, as well as susceptibility to ventricular arrhythmias in T2DM. Based on above data, we conclude that H2O2 overproduction inactivates Cav2.2 channels and further contributes to ventricular vagal dysfunction and ventricular arrhythmogenesis in T2DM, suggesting that H2O2 signaling pathway might be an effective therapeutic target to suppress ventricular arrhythmias in patients with T2DM.