BS12 Succinate disrupts human and mouse atrial action potentials and modifies sodium channel kinetics

Introduction Mitochondrial succinate metabolism in the heart during acute or chronic hypoxia is a major cause of cellular death and dysfunction. However, its impact on cardiac electrical function is largely unknown. This could be of importance given that atrial and ventricular arrhythmias are very common following ischaemia/reperfusion. This study analysed the effects of succinate on human and mouse atrial action potentials (APs) and sodium currents (INa), to identify potential proarrhythmic electrical remodelling. Methods Whole murine left atria (LA) and dissociated LA cardomyocytes were obtained from adult male and female mice (7–16W, FVB background). Electrophysiological experiments were also performed on human induced pluripotent stem cell-derived atrial cardiomyocytes (hiPSC-aCMs) and HEK293 cells expressing the human cardiac sodium channel, hNav1.5. APs and INa were recorded using intracellular microelectrode and whole-cell patch clamp techniques, in the presence and absence of diethyl succinate (DES, 1–10 mM); a cell permeable form of succinate. Data is presented in text as mean±SEM, significance was taken as two-sided p<0.05, assessed using an unpaired Student's t-test or one-way ANOVA with Bonferroni post-hoc analysis. Results In isolated murine LA, DES caused a concentration-dependent reduction in the peak AP upstroke velocity (Vmax: Time control 188±3 V/s, 5 mM DES 161±8 V/s, 10 mM DES 101±14 V/s, n=16 LA, p<0.05). Similarly, DES significantly decreased the Vmax in hiPSC-aCMs, an effect that was not reversible (Control 123±10 V/s, 5 mM DES 87±9 V/s, Washout 91±9, n=9 cells, p<0.05). In dissociated murine LA cells, 5 mM DES inhibited INa, with an enhanced action at more positive holding potentials (VH: -100 mV 34±3% inhibition vs -80 mV 69±7% inhibition, n=14 cells, p<0.05). This was associated with an approximately 10 mV negative shift in V50 of inactivation (Control -82±2 mV vs DES -91±1 mV, n=14 cells, p<0.05). In HEK293 cells stably expressing hNav1.5, DES also produced a significant left-shift in the V50 of inactivation (Control -84±1 mV vs DES -89±1 mV, n=10 cells, p<0.05). Conclusion Succinate inhibits human and murine cardiac INa, primarily by reducing steady state channel availability. This is likely to account for the observed reduction in peak AP upstroke velocity, potentially increasing the risk of conduction disturbances and atrial fibrillation. Conflict of Interest No