Regulation of cardiac calcium signaling by newly identified calcium pump modulators.

In cardiomyocytes, the sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA2a) is a central component of intracellular Ca(2+) 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 Ca(2+) uptake activity. In this study, confocal microscopy and in-cell Ca(2+) imaging were used to characterize the effects of these SERCA2a activators on Ca(2+) regulation in mouse ventricular myocytes and endoplasmic reticulum (ER) Ca(2+) uptake in a HEK293 cell expressing human SERCA2a. Analysis of cytosolic Ca(2+) dynamics in cardiomyocytes revealed that both Compounds (6 and 8) increase the action potential-induced Ca(2+) transients and sarcoplasmic reticulum (SR) Ca(2+) load. While Compound 6 induced a negligible effect on Ca(2+) transients invoked by the L-type Ca(2+) channel (LTCC) current, Compound 8 increased Ca(2+) transients during LTCC activation, suggesting an off-target protein interaction of Compound 8. Analysis of ER Ca(2+) transport by human SERCA2a in HEK cells showed that only Compound 6 increased both ER Ca(2+) uptake and ER Ca(2+) load significantly, whereas Compound 8 had no effect on SERCA2a Ca(2+) transport. This study revealed that Compound 6 exhibits promising characteristics that can improve intracellular Ca(2+) dynamics by selectively enhancing SERCA2a Ca(2+) uptake.