JTV519 (K201) reduces sarcoplasmic reticulum Ca2+ leak and improves diastolic function in vitro in murine and human non‐failing myocardium

BACKGROUND AND PURPOSE Ca2+ leak from the sarcoplasmic reticulum (SR) via ryanodine receptors (RyR2s) contributes to cardiomyocyte dysfunction. RyR2 Ca2+ leak has been related to RyR2 phosphorylation. In these conditions, JTV519 (K201), a 1,4‐benzothiazepine derivative and multi‐channel blocker, stabilizes RyR2s and decrease SR Ca2+ leak. We investigated whether JTV519 stabilizes RyR2s without increasing RyR2 phosphorylation in mice and in non‐failing human myocardium and explored underlying mechanisms.EXPERIMENTAL APPROACH SR Ca2+ leak was induced by ouabain in murine cardiomyocytes. [Ca2+]‐transients, SR Ca2+ load and RyR2‐mediated Ca2+ leak (sparks/waves) were quantified, with or without JTV519 (1 µmol·L−1). Contribution of Ca2+‐/calmodulin‐dependent kinase II (CaMKII) was assessed by KN‐93 and Western blot (RyR2‐Ser2814 phosphorylation). Effects of JTV519 on contractile force were investigated in non‐failing human ventricular trabeculae.KEY RESULTS Ouabain increased systolic and diastolic cytosolic [Ca2+]i, SR [Ca2+], and SR Ca2+ leak (Ca2+ spark (SparkF) and Ca2+ wave frequency), independently of CaMKII and RyR‐Ser2814 phosphorylation. JTV519 decreased SparkF but also SR Ca2+ load. At matched SR [Ca2+], Ca2+ leak was significantly reduced by JTV519, but it had no effect on fractional Ca2+ release or Ca2+ wave propagation velocity. In human muscle, JTV519 was negatively inotropic at baseline but significantly enhanced ouabain‐induced force and reduced its deleterious effects on diastolic function.CONCLUSIONS AND IMPLICATIONS JTV519 was effective in reducing SR Ca2+ leak by specifically regulating RyR2 opening at diastolic [Ca2+]i in the absence of increased RyR2 phosphorylation at Ser2814, extending the potential use of JTV519 to conditions of acute cellular Ca2+ overload.