Structural and functional modifications of phospholamban and regulation of calcium transport in the sarcoplasmic reticulum under conditions of metabolic cardiac insufficiency

The phosphorylation of phospholamban from dog myocardium is shown to correlate with the protein sensitivity to tryptic attack both in undamaged myocardium and under conditions of circulatory hypoxia and experimental infarction. In the absence of "exogenous" protein kinase a decreased phosphorylation of phospholamban is observed in the incubation mixture containing 10(-6) M cAMP both for circulatory hypoxia and myocardial infarction. In the latter case the phosphorylation remains diminished in the presence of "exogenous" protein kinase as well. The sarcoplasmic reticulum from damaged myocardium exhibited changes in the velocity of the oxalate-dependent transport of calcium which correlated with the corresponding degree of the phospholamban phosphorylation.