14-3-3 Enables β-Adrenergic Regulation of the Cardiac Sodium Channel at the Intercalated Disc

Background: Beta-Adrenergic stimulation enables the heart to adapt electrical activity to increased physiological demand. Although the cardiac sodium channel Nav1.5 is essential for impulse propagation, the mechanisms underlying its acute beta-adrenergic regulation, particularly within distinct cardiomyocyte membrane domains, remain poorly understood. We investigated whether the phosphorylation-sensitive adaptor protein 14-3-3 mediates this regulation. Methods and Results: Using automated patch-clamp electrophysiology in HEK293 cells and human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs), we found that isoproterenol rapidly increased sodium current (INa) and promoted channel activation at more hyperpolarized potentials, whereas PKA inhibition reduced INa. Disruption of 14-3-3 function abolished these responses without substantially altering basal sodium current or Nav1.5 surface expression. Macropatch recordings from ventricular myocytes revealed that isoproterenol preferentially enhanced INa at the intercalated disc, an effect prevented by 14-3-3 inhibition. Proximity ligation assays further demonstrated increased Nav1.5/14-3-3 proximity following beta-adrenergic stimulation. Systematic mutagenesis identified S460 in the Nav1.5 DI-DII linker as a critical determinant of acute PKA-dependent regulation. Molecular modeling predicted that S460 phosphorylation stabilizes the Nav1.5/14-3-3 interaction. In CRISPR-engineered S460A iPSC-CMs, acute beta-adrenergic regulation of INa was abolished, whereas the isoproterenol-induced increase in conduction velocity was significantly attenuated. Computational simulations further predicted that enhanced intercalated-disc sodium current supports increased conduction velocity across varying conditions of electrical coupling and pacing rate. Conclusions: Our findings identify 14-3-3 and S460 as critical determinants of spatially selective beta-adrenergic regulation of Nav1.5 at the cardiac intercalated disc. This mechanism provides a molecular link between sympathetic signaling and cardiac sodium current regulation, supporting the concept that localized enhancement of Nav1.5 function contributes to the adaptation of cardiac conduction during increased sympathetic demand.