PLN and familial dilated cardiomyopathy: While catalytic efficiency of PKAc with PLN R9C only decreases by ~twofold, a corresponding change in phosphorylation level of PLN could be consistent with the relatively mild symptoms of DCM, and even a small increase in SERCA inhibition resulting from such a decrease in PLN phosphorylation would likely compound the Ca2+ imbalance in the cell over repeated cycles of cardiac muscle contraction and relaxation.