Abstract 941: Metabolic Regulation Of Na+ Current, A Possible Explanation Of Glycerol-3-phosphate Dehydrogenase-linked Brugada Syndrome
Brugada Syndrome (BrS) is a life threatening autosomal dominant disorder associated with decreased cardiac sodium channel (SCN5A) current. Recently, we reported a mutation (MT) in the glycerol-3-phosphate dehydrogenase 1-like (GPD1-L) gene causes BrS by reducing Na+ current. Nevertheless, the mechanism for this reduction is unclear. The GPD family of genes is involved in NADH-dependent energy metabolism, and GDP1-L has >75% amino acid homology with GPD. Therefore, we tested the effect on NADH levels of transfecting HEK 293 cells with wild-type (WT) and MT GPD1-L. MT GPD1- L raised cellular NADH level by 3 fold (p<0.01). Incubated of HEK cells stably expressing the human cardiac Na+ channel (SCN5A) overnight with 300 μM extracellular NADH decreased whole cell peak conductance by 71.4% (p<0.001, n=17 ), while 300 μM extracellular NAD+ caused a 30.3% increase (p< 0.001, n = 9). Neither treatment affected cell viability. Application of 100 μM intracellular NADH had an immediate effect, decreasing Na+ current by 55.5% (p < 0.001, n=9) at 10 min, while 100 μM intracellular NAD+ showed an increase in current by 66.6% (p < 0.01, n =10) over the same time frame. The NADH changes were similar to the 69.9% reduction seen when transfecting HEK cells with MT GPD1-L. External NAD+ could prevent the reduction in Na+ current caused by MT GPD1-L. Fluorescent microscopy showed that NADH and MT GPD1-L resulted in statistically significant 6.1 and 6.9 fold reductions in membrane-associated, GFP-tagged Na+ channels. In conclusion, MT GPD1-L raised intracellular NADH, reduced Na+ currents, and decreased membrane associated Na+ channels. These effects were similar to those seen with exogenous NADH, suggesting that GPD1-L may cause BrS by altering NADH levels. These results may hold implications for arrhythmic risk associated with other cardiac metabolic derangements.