Long-term treatment with ivabradine in transgenic atrial fibrillation mice counteracts hyperpolarization-activated cyclic nucleotide gated channel overexpression.

ABSTRACT

INTRODUCTION: Recent studies have demonstrated that ivabradine (IVA), is a selective inhibitor of funny current (If) and exerts antiarrhythmic effects in the settings of various diseases such as heart failure and myocardial ischemia. However, little is known regarding the effects of long-term IVA treatment on If current and hyperpolarization-activated cyclic nucleotide gated (HCN) channel overexpression. METHODS AND RESULTS: We investigated both the If current and HCN channel expression in wild-type (WT) mice and transgenic (TG) atrial fibrillation (AF) mice (heart-specific overexpressing of (pro) renin receptor TG mice) and examined the effects of IVA on the If current and HCN channel expression, and whether those effects were sufficient to prevent an AF episode. Compared with WT mice, the If current density (at -170 mV TG, -39.6 ± 4.6 pA/pF; WT, -26.9 ± 3.0 pA/pF; P < 0.001) and activation kinetics (V1/2 TG, -109.45 ± 1.35 mV; WT, -128.20 ± 1.65 mV), as well as HCN2 and HCN4 messenger RNA expression and HCN4 protein expression were significantly increased in the atrial myocytes of TG mice. After 4 months of IVA treatment (7 mg/kg per day orally) the effects of IVA on TG AF mice were accompanied by the inhibition of upregulation of HCN2 and HCN4 protein expression in atrial tissue, and then resulted in a uniform If loss of function. Furthermore, we observed that ivabradine significantly decreased the incidence of AF in the TG mice (41.2% in TG mice, 16.7% in TG + IVA mice; P < 0.01). CONCLUSION: IVA reduced the incidence of AF in mice, and the antiarrhythmic effects of IVA are not limited to heart rate reduction, as they partially counteract HCN overexpression and reverse electrophysiological cardiac remodeling by attenuating If gain-of-function.