Molecular regulation of phospholamban function and expression.

Intracellular levels of cAMP regulated by the beta-adrenergic actions of catecholamines play a key in the metabolic, electrical, and mechanical performance of the cardiac muscles. Among a number of biological actions of cAMP, the excitation-contraction coupling process in cardiac myocytes is markedly affected by cAMP through its stimulatory effect on cAMP-dependent protein kinase. Phospholamban, which is expressed in the sarcoplasmic reticulum of cardiac, slow-twitch skeletal, and smooth muscles, is one of the substrates for cAMP-dependent protein kinase. Phospholamban regulates the activity of Ca ATPase in the sarcoplasmic reticulum membranes in a manner dependent on the phosphorylation state of cAMP-dependent protein kinase, thereby changing the mechanical performance of the cardiac muscles. This Ca regulatory mechanism of phospholamban-Ca ATPase system is mediated by a direct protein-protein interaction between two proteins. This review focuses on recent advances in understanding the role of phospholamban molecule in the regulation of Ca transport by cardiac muscle sarcoplasmic reticulum.