Empagliflozin Ameliorates Ouabain-Induced Na+ and Ca2+ Dysregulations in Ventricular Myocytes in an Na+-Dependent Manner

Abstract

Purpose: Sodium-glucose cotransporter 2 (SGLT2) inhibitors are a novel class of glucose-lowering agents that have improved clinical outcomes in patients with heart failure; however, their therapeutic mechanisms remain elusive. Although contradictory results have been reported, it has been proposed that improving Na⁺ homeostasis may be the underlying mechanism of action of SGLT2 inhibitors in heart failure treatment. This study explored whether empagliflozin ameliorates Na⁺ and Ca²⁺ handling disorders induced by ouabain in an Na⁺-dependent manner.

Methods: Isolated ventricular myocytes of mice were incubated with ouabain to establish a cellular model of Na⁺ overload. Effects of empagliflozin on Na⁺ and Ca²⁺ handling were evaluated using an ionOptix system and a confocal microscope. Distinct cytosolic Na⁺ levels were established by incubating different ouabain concentrations (10, 50, and 100 μmol/L).

Results: In the absence of ouabain, 1 μmol/L empagliflozin had a negligible impact on Na⁺ and Ca²⁺ handling in ventricular myocytes. Ouabain (50 μmol/L) significantly enhanced cytosolic Na⁺ levels and dysregulated Ca²⁺ handling, including an increased Ca²⁺ transient amplitude, elevated Ca²⁺ content in the sarcoplasmic reticulum, and enhanced spontaneous Ca²⁺ release normalized by treatment with 1 μmol/L empagliflozin within 10 min. All Na⁺ and Ca²⁺ handling abnormalities induced by ouabain were reversed by 1 μmol/L empagliflozin. The efficacy of empagliflozin was more potent at higher cytosolic Na⁺ levels. Pretreatment with the Na⁺/H⁺ exchanger (NHE) inhibitor (1 μmol/L cariporide) abolished the effects of empagliflozin.

Conclusion: Empagliflozin ameliorates ouabain-induced Na⁺ and Ca²⁺ handling disorders in a cytosolic Na⁺-dependent manner, potentially by inhibiting the NHE.

Keywords: Ca2+ handling; Empagliflozin; Na+ handling; Sodium-glucose cotransporter 2 inhibitors; Sodium-hydrogen exchanger.