Abstract
BACKGROUND: Elevated myocardial intracellular sodium ([Na(+)](i)) was shown to decrease mitochondrial calcium ([Ca(2+)](MITO)) via mitochondrial sodium/calcium exchanger (NCX(MITO)), resulting in decreased mitochondrial ATP synthesis. The sodium-glucose co-transporter 2 inhibitor (SGLT2i) ertugliflozin (ERTU) improved energetic deficit and contractile dysfunction in a mouse model of high fat, high sucrose (HFHS) diet-induced diabetic cardiomyopathy (DCMP). As SGLT2is were shown to lower [Na(+)](i) in isolated cardiomyocytes, we hypothesized that energetic improvement in DCMP is at least partially mediated by a decrease in abnormally elevated myocardial [Na(+)](i). METHODS: Forty-two eight-week-old male C57BL/6J mice were fed a control or HFHS diet for six months. In the last month, a subgroup of HFHS-fed mice was treated with ERTU. At the end of the study, left ventricular contractile function and energetics were measured simultaneously in isolated beating hearts by (31)P NMR (Nuclear Magnetic Resonance) spectroscopy. A subset of untreated HFHS hearts was perfused with vehicle vs. CGP 37157, an NCX(MITO) inhibitor. Myocardial [Na(+)](i) was measured by (23)Na NMR spectroscopy. RESULTS: HFHS hearts showed diastolic dysfunction, decreased contractile reserve, and impaired energetics as reflected by decreased phosphocreatine (PCr) and PCr/ATP ratio. Myocardial [Na(+)](i) was elevated > 2-fold in HFHS (vs. control diet). ERTU reversed the impairments in HFHS hearts to levels similar to or better than control diet and decreased myocardial [Na(+)](i) to control levels. CGP 37157 normalized the PCr/ATP ratio in HFHS hearts. CONCLUSIONS: Elevated myocardial [Na(+)](i) contributes to mitochondrial and contractile dysfunction in DCMP. Targeting myocardial [Na(+)](i) and/or NCX(MITO) may be an effective strategy in DCMP and other forms of heart disease associated with elevated myocardial [Na(+)](i).