Abstract 2568: Metabolic Control of Cardiac Na+ Current Through Pyridine Nucleotides
Background: Mutations in glycerol-3-phosphate dehydrogenase 1-like (GPD1-L) protein reduce cardiac Na+ current (INa) and cause Brugada Syndrome. GPD1-L has >80% amino acid homology with glycerol-3-phosphate dehydrogenase that is involved in nicotinamide adenine dinucleotides (NAD)-dependent energy metabolism. We therefore tested whether NAD(H) could regulate human cardiac sodium channel (SCN5A).
Methods: We used HEK293 cells stably expressing Nav1.5 and rat neonatal cardiomyocytes to assess effects of NAD(H) on INa by whole-cell patch clamp recording. The effects of a GPD1-L mutation, A280V, on intracellular NAD(H) levels were examined in HEK293 cells. The effect of NAD+ on arrhythmic risk resulting from decreased INa was evaluated in SCN5A+/− mice.
Results: A280V GPD1-L caused a 2.48±0.17-fold increase of intracellular NADH level (P<0.001). In cardiomyocytes, intracellular NADH application (500 μM) or co-transfection with A280V GPD1-L resulted in decreased INa (0.48±0.09 and 0.19±0.06 of control group, P<0.01), which was reversed by NAD±. In HEK cells, A280V GPD1-L or NADH application resulted in a decrease of INa that was reversed by NAD+, a protein kinase C (PKC) inhibitor chelerythrine, superoxide dismutase (SOD), or rotenone. The decreased INa induced by PMA (a PKC activator, 0.40±0.07 of control group, P<0.01) was prevented by SOD. Consistent with this, antimycin A, a mitochondrial inhibitor known to generate superoxide, decreased INa (0.51±0.07 of control group, P<0.001). The effect of NAD+ to antagonize the Na+ channel downregulation by A280V GPD1-L or NADH was prevented by a protein kinase A (PKA) inhibitor, PKAI6 –22, and mimicked by a PKA activator, forskolin. Extracellular application of NAD+ (100 μM) to SCN5A+/− mouse hearts ameliorated the risk of ventricular tachycardia.
Conclusions: NAD(H) balance acutely regulates Na+ channel current. A280V GPD1-L appears to regulate Nav1.5 by altering the oxidized to reduced NAD(H) balance, suggesting a link between metabolism and SCN5A. This reduction in INa requires PKC activation and is mediated by superoxide from the mitochondria. NAD+ prevents these effects by activating PKA and could represent a therapy for arrhythmic risk associated with reduced INa.
This research has received full or partial funding support from the American Heart Association, National Center.