Rationale: Mutations in glycerol-3-phosphate dehydrogenase 1-like (GPD1-L) protein reduce cardiac Na⁺ current (I_Na) and cause Brugada Syndrome (BrS). GPD1-L has >80% amino acid homology with glycerol-3-phosphate dehydrogenase, which is involved in NAD-dependent energy metabolism.

Objective: Therefore, we tested whether NAD(H) could regulate human cardiac sodium channels (Na_v1.5).

Methods and Results: HEK293 cells stably expressing Na_v1.5 and rat neonatal cardiomyocytes were used. The influence of NADH/NAD⁺ on arrhythmic risk was evaluated in wild-type or SCN5A^+/- mouse heart. A280V GPD1-L caused a 2.48±0.17-fold increase in intracellular NADH level (P<0.001). NADH application or cotransfection with A280V GPD1-L resulted in decreased I_Na (0.48±0.09 or 0.19±0.04 of control group, respectively; P<0.01), which was reversed by NAD⁺, chelerythrine, or superoxide dismutase. NAD⁺ antagonism of the Na⁺ channel downregulation by A280V GPD1-L or NADH was prevented by a protein kinase (PK)A inhibitor, PKAI_6–22. The effects of NADH and NAD⁺ were mimicked by a phorbol ester and forskolin, respectively. Increasing intracellular NADH was associated with an increased risk of ventricular tachycardia in wild-type mouse hearts. Extracellular application of NAD⁺ to SCN5A^+/- mouse hearts ameliorated the risk of ventricular tachycardia.

Conclusions: Our results show that Na_v1.5 is regulated by pyridine nucleotides, suggesting a link between metabolism and I_Na. This effect required protein kinase C activation and was mediated by oxidative stress. NAD⁺ could prevent this effect by activating PKA. Mutations of GPD1-L may downregulate Na_v1.5 by altering the oxidized to reduced NAD(H) balance.