Impaired sinoatrial node function and increased susceptibility to atrial fibrillation in mice lacking natriuretic peptide receptor C

Key points: Natriuretic peptides (NPs) elicit their effects via multiple NP receptors (including NPR-A, NPR-B and NPR-C, with NPR-C being relatively poorly understood). We have studied the effects of NPR-C ablation on cardiac structure, function and arrhythmogenesis using NPR-C knockout (NPR-C^-/-) mice. NPR-C^-/- mice are characterized by sinoatrial node (SAN) dysfunction and a profound increase in susceptibility to atrial fibrillation. Increased susceptibility to arrhythmias in NPR-C^-/- mice was associated with slowed electrical conduction in the SAN as well as the right and left atria due to enhanced collagen expression and deposition in the atria (structural remodelling), but without changes in action potential morphology (electrical remodelling) in isolated SAN or atrial myocytes. This study demonstrates a critical protective role for NPR-C in the heart. Natriuretic peptides (NPs) are critical regulators of the cardiovascular system that are currently viewed as possible therapeutic targets for the treatment of heart disease. Recent work demonstrates potent NP effects on cardiac electrophysiology, including in the sinoatrial node (SAN) and atria. NPs elicit their effects via three NP receptors (NPR-A, NPR-B and NPR-C). Among these receptors, NPR-C is poorly understood. Accordingly, the goal of this study was to determine the effects of NPR-C ablation on cardiac structure and arrhythmogenesis. Cardiac structure and function were assessed in wild-type (NPR-C^+/+) and NPR-C knockout (NPR-C^-/-) mice using echocardiography, intracardiac programmed stimulation, patch clamping, high-resolution optical mapping, quantitative polymerase chain reaction and histology. These studies demonstrate that NPR-C^-/- mice display SAN dysfunction, as indicated by a prolongation (30%) of corrected SAN recovery time, as well as an increased susceptibility to atrial fibrillation (6% in NPR-C^+/+ vs. 47% in NPR-C^-/-). There were no differences in SAN or atrial action potential morphology in NPR-C^-/- mice; however, increased atrial arrhythmogenesis in NPR-C^-/- mice was associated with reductions in SAN (20%) and atrial (15%) conduction velocity, as well as increases in expression and deposition of collagen in the atrial myocardium. No differences were seen in ventricular arrhythmogenesis or fibrosis in NPR-C^-/- mice. This study demonstrates that loss of NPR-C results in SAN dysfunction and increased susceptibility to atrial arrhythmias in association with structural remodelling and fibrosis in the atrial myocardium. These findings indicate a critical protective role for NPR-C in the heart.