Regulation of cardiac calcium signaling by newly identified calcium pump modulators

In cardiomyocytes, the sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA2a) is a central component of intracellular Ca²⁺ regulation. Several heart diseases, including heart failure, are associated with reduced myocardial contraction due to SERCA2a downregulation. Therefore, the need for developing new drugs that could improve SERCA2a function is high. We have recently identified SERCA2a modulators (Compounds 6 and 8) from our screening campaigns and confirmed activation of biochemical SERCA2a ATPase activity and Ca²⁺ uptake activity. In this study, confocal microscopy and in-cell Ca²⁺ imaging were used to characterize the effects of these SERCA2a activators on Ca²⁺ regulation in mouse ventricular myocytes and endoplasmic reticulum (ER) Ca²⁺ uptake in a HEK293 cell expressing human SERCA2a. Analysis of cytosolic Ca²⁺ dynamics in cardiomyocytes revealed that both Compounds (6 and 8) increase the action potential-induced Ca²⁺ transients and sarcoplasmic reticulum (SR) Ca²⁺ load. While Compound 6 induced a negligible effect on Ca²⁺ transients invoked by the L-type Ca²⁺ channel (LTCC) current, Compound 8 increased Ca²⁺ transients during LTCC activation, suggesting an off-target protein interaction of Compound 8. Analysis of ER Ca²⁺ transport by human SERCA2a in HEK cells showed that only Compound 6 increased both ER Ca²⁺ uptake and ER Ca²⁺ load significantly, whereas Compound 8 had no effect on SERCA2a Ca²⁺ transport. This study revealed that Compound 6 exhibits promising characteristics that can improve intracellular Ca²⁺ dynamics by selectively enhancing SERCA2a Ca²⁺ uptake.