부산대학교 도서관

Introduction: The effects of empagliflozin on excitation-contraction coupling (ECC) have not been fully elucidated. We previously showed that empagliflozin directly reduces Ca/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]cytosolic are only decreased after 24 h empagliflozin.Hypothesis: We hypothesize that empagliflozin reduces cardiac late Na current (late INa) via a reduction in CaMKII activity. We further hypothesize that Na/Ca-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 H2O2 or ATX-II to induce late INa. Whole-cell patch clamp was used to measure late INa or INCX. Epifluorescence with SBFI was used to obtain cardiac [Na]. Some CM were treated with NCX inhibitor KB-R7943 (5 μM).Results and Conclusions: Late INa induced by H2O2 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 NaV1.5, no effect of empagliflozin on late INa was present (also not under ATX-II stimulation). As shown before, subsarcolemmal [Na] estimated via patch clamp (Nernst equation) was already reduced after 30min (T30min). However, empagliflozin did not acutely reduce cytosolic [Na] at T30min, 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 T30min. Matching this, NCX forward mode (patch clamp) was acutely induced by empagliflozin at T30min, thus resulting in Na influx that initially masks the reduction in [Na] resulting from a reduction in late INa. This may explain why Na/Ca 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.