Ankyrin-G coordinates intercalated disc signaling platform to regulate cardiac excitability in vivo

Rationale: Na_v1.5 (SCN5A) is the primary cardiac voltage-gated Na_v channel. Na_v1.5 is critical for cardiac excitability and conduction, and human SCN5A mutations cause sinus node dysfunction, atrial fibrillation, conductional abnormalities, and ventricular arrhythmias. Further, defects in Na_v1.5 regulation are linked with malignant arrhythmias associated with human heart failure. Consequently, therapies to target select Na_v1.5 properties have remained at the forefront of cardiovascular medicine. However, despite years of investigation, the fundamental pathways governing Na_v1.5 membrane targeting, assembly, and regulation are still largely undefined. Objective: Define the in vivo mechanisms underlying Na_v1.5 membrane regulation. Methods and Results: Here, we define the molecular basis of an Na_v channel regulatory platform in heart. Using new cardiac-selective ankyrin-G^-/- mice (conditional knock-out mouse), we report that ankyrin-G targets Na_v1.5 and its regulatory protein calcium/calmodulin-dependent kinase II to the intercalated disc. Mechanistically, β_IV-spectrin is requisite for ankyrin-dependent targeting of calcium/calmodulin-dependent kinase II-δ however, β_IV-spectrin is not essential for ankyrin-G expression. Ankyrin-G conditional knock-out mouse myocytes display decreased Na_v1.5 expression/membrane localization and reduced I_Na associated with pronounced bradycardia, conduction abnormalities, and ventricular arrhythmia in response to Na_v channel antagonists. Moreover, we report that ankyrin-G links Na_v channels with broader intercalated disc signaling/structural nodes, as ankyrin-G loss results in reorganization of plakophilin-2 and lethal arrhythmias in response to β-adrenergic stimulation. Conclusions: Our findings provide the first in vivo data for the molecular pathway required for intercalated disc Na_v1.5 targeting/regulation in heart. Further, these new data identify the basis of an in vivo cellular platform critical for membrane recruitment and regulation of Na_v1.5. (Circ Res. 2014;115:929-938.)