Overexpression of M3 Muscarinic Receptor Suppressed Adverse Electrical Remodeling in Hypertrophic Myocardium Via Increasing Repolarizing K+ Currents

Abstract

Background/Aims: Cardiac hypertrophy (CH) is an adaptive response to diverse cardiovascular conditions, which is accompanied by adverse electrical remodeling manifested as abnormal K+ channel activities. M3 subtype of muscarinic acetylcholine receptor (M3-mAChR) is a novel regulator of cardiac electrical activity. In this study we aim to explore if the overexpression of M3-mAChR could attenuate the adverse electrical remodeling in CH and then uncover its underlying electrophysiological mechanisms. Methods: Transgenic mice with M3-mAChR overexpression (M3-TG) and wild type (WT) mice were subjected to transverse aortic constriction (TAC) to induce CH. Myocardial hypertrophy and cardiac function were quantified by the measurement of echocardiography, electrocardiogram, heart weight and tibia length. Whole-cell and signal-cell patch-clamp were employed to record electrophysiological properties by acute isolation of acutely isolated ventricular cardiomyocytes and Western blot was carried out to evaluate the Kir2.1and Kv4.2/4.3 protein levels in left ventricular tissue. Results: Compared with WT group, the elevation of cardiac index, including heart weight/body weight index and heart weight/tibia length index confirmed the myocardial hypertrophic growth induced by TAC. Echocardiography detection revealed that the TAC-treated mice showed an obvious increase in the thickness of left ventricular posterior wall (LVPW) and ejection fraction (EF) due to compensatory hypertrophy, which attenuated by the overexpression of M3-mAChR. Pressure overload induced a prolongation of QTc interval in WT mice, an effect blunted in M3-TG mice. Furthermore, compared with WT mice, M3-mAChR overexpression in hypertrophic myocardium accelerated cardiac repolarization and shortened action potential duration, and thus correcting the prolongation of QTc interval. Moreover, M3-TG mice have the greater current density of IK1 and Ito in ventricular myocytes after TAC compared with WT mice. Finally, compared with WT mice, M3-TG mice expressed higher levels of Kir2.1 in ventricular myocytes. Conclusion: M3-mAChR overexpression protected against adverse electrical remodeling in CH by enhancing potassium currents and promoting repolarization.