Introduction: Glycerol-3-phosphate dehydrogenase 1-like (GPD1-L) mutations have been shown to reduce cardiac Na+ current and cause Brugada Syndrome. Our previous work suggests that mutations in GPD1-L act through NAD(H) to alter Na+ current. NADH results in downregulation of Na+ current and NAD+ can reverse the downregulation of Na+ current by mutant (MT) GPD1-L or NADH. Here, we studied potential signaling pathways between GPD1-L, NAD(H), and Na+ channel.Methods: Currents were measured using whole-cell patch clamp of HEK cells stably expressing the human cardiac sodium channel with and without chelerythrine (a PKC inhibitor, IC50 = 660 nM), PKAI6-22 (a PKA inhibitor, IC50 = 1.6 nM), apocynin (a NADPH oxidase inhibitor), or elevated intracellular Ca2+ in the pipette solution. MT GPD1-L (A280V) was co-transfected with red fluorescent protein with Fugene6 to HEK cells 40 hours prior to measuring current.Results: The 2-fold reduction in Na+ current mediated by NADH (100 μM) was inhibited by 200 μM apocynin (50±6% vs. 86±15% of the control current, n=14, p<0.001), 6 mM [Ca2+]i (107±17% of control, n=12, p<0.001), or 10 μM chelerythrine (86±14% of control, n=10, p<0.05). PKAI6-22 blocked the NAD+-mediated upregulation of Na+ currents in the presence of MT GPD1-L (n=10, p<0.001). Chelerythrine (10-50 μM) or PKAI6-22 (50 nM - 5 μM) alone did not affect the peak currents of Na+ channels.Conclusions: Our experiments suggest that NAD(H) can alter Na+ currents. Downregulation by NADH seems to involve the NADPH oxidase and PKC. PKA appears to be involved in NAD+-dependent current upregulation. This implies that redox/metabolic state can influence Na+ current.