Abstract 9419: Empagliflozin Modulates Cardiac Na Homeostasis via Late I _Na and I _NCX

Introduction: The effects of empagliflozin on excitation-contraction coupling (ECC) have not been fully elucidated. We previously showed that empagliflozin directly reduces Ca 2+ /calmodulin kinase II (CaMKII) activity in human and murine heart failure, thereby improving contraction. Upon acute exposure, however, only subsarcolemmal [Na + ] is decreased, while [Na + ] cytosolic and [Ca 2+ ] cytosolic are only decreased after 24 h empagliflozin. Hypothesis: We hypothesize that empagliflozin reduces cardiac late Na current (late I Na ) via a reduction in CaMKII activity. We further hypothesize that Na + /Ca 2+ -exchanger (NCX) is acutely masking effects on cardiac [Na + ], thereby delaying downstream effects on cardiac ECC. Methods: Informed consent was obtained according to the Declaration of Helsinki. Human/murine cardiomyocytes (CM) were isolated and incubated with 1 μM empagliflozin for 30 min or 24 h. Some CM were treated with H 2 O 2 or ATX-II to induce late I Na . Whole-cell patch clamp was used to measure late I Na or I NCX . Epifluorescence with SBFI was used to obtain cardiac [Na + ]. Some CM were treated with NCX inhibitor KB-R7943 (5 μM). Results and Conclusions: Late I Na induced by H 2 O 2 was acutely inhibited in human and murine CM by empagliflozin, similar to CaMKII inhibition with AIP (2 μM). In CM lacking CaMKII or the CaMKII phosphosite S571 on Na V 1.5, no effect of empagliflozin on late I Na was present (also not under ATX-II stimulation). As shown before, subsarcolemmal [Na + ] estimated via patch clamp (Nernst equation) was already reduced after 30min (T30 min ). However, empagliflozin did not acutely reduce cytosolic [Na + ] at T30 min , but potently did so after 24h exposure (SBFI measurement). Acute inhibition of NCX with KB-R7943 showed no effect on cardiac Na + , but when performed in addition to empagliflozin, potently reduced [Na + ] already at T30 min . Matching this, NCX forward mode (patch clamp) was acutely induced by empagliflozin at T30 min , thus resulting in Na + influx that initially masks the reduction in [Na + ] resulting from a reduction in late I Na . This may explain why Na + /Ca 2+ homeostasis is only affected after 24h empagliflozin exposure. Our results may explain discrepant results on ECC by different groups on acute vs. prolonged empagliflozin exposure.