Phosphodiesterase-1 inhibitor modulates Ca2+ regulation in sirtuin 1-deficient mouse cardiomyocytes.

ABSTRACT

BACKGROUND: Phosphodiesterase inhibitors can be used to enhance second messenger signaling to regulate intracellular Ca2+ cycling. This study investigated whether ITI-214, a selective phosphodiesterase-1 inhibitor, modulates intracellular Ca2+ regulation, resulting in a positive inotropic effect in sirtuin 1 (Sirt1)-deficient cardiomyocytes. METHODS: Mice with cardiac-specific Sirt1 knockout (Sirt1-/-) were used, with Sirt1flox/flox mice serving as controls. Electromechanical analyses of ventricular tissues were conducted, and we monitored intracellular Ca2+ using Fluo-3 as well as reactive oxygen species production in isolated cardiomyocytes. RESULTS: Sirt1-/- ventricles showed prolonged action potential duration at 90% repolarization and increased contractile force after treatment with ITI-214. The rates and sustained durations of burst firing in ventricles were higher and longer, respectively, in Sirt1-/- ventricles than in controls. ITI-214 treatment decreased the rates and shortened the durations of burst firing in Sirt1-/- mice. Sirt1-/- cardiomyocytes showed reduced Ca2+ transient amplitudes and sarcoplasmic reticulum (SR) Ca2+ stores compared to those in control cardiac myocytes, which was reversed after ITI-214 treatment. SR Ca2+ leakage was larger in Sirt1-/- cardiac myocytes than in control myocytes. ITI-214 reduced SR Ca2+ leakage in Sirt1-/- cardiac myocytes. Increased levels of reactive oxygen species in Sirt1-/- cardiomyocytes compared to those in controls were reduced after ITI-214 treatment. Levels of Ca2+ regulatory proteins, including ryanodine receptor 2, phospholamban, and sarcoplasmic/endoplasmic reticulum Ca2+ ATPase 2a were not affected by ITI-214 administration. CONCLUSIONS: Our results suggest that ITI-214 improves intracellular Ca2+ regulation, which in turn exerts inotropic effects and suppresses arrhythmic events in Sirt1-deficient ventricular myocytes.