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

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.

Mice with cardiac-specific Sirt1 knockout (Sirt1^-/-) were used, with Sirt1^flox/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.

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.

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.