Myocardial glycogen dynamics: new perspectives on disease mechanisms.

Cardiac glycogen regulation involves a complex interplay between multiple signalling pathways, allosteric activation of enzymes, and sequestration for autophagic degradation. Signalling pathways appear to converge on glycogen regulatory enzymes via insulin (glycogen synthase kinase 3β, protein phosphatase 1, allosteric action of glucose-6-phosphate), β-adrenergic (phosphorylase kinase protein phosphatase 1 inhibitor), and 5' adenosine monophosphate-activated protein kinase (allosteric action of glucose-6-phosphate, direct glycogen binding, insulin receptor). While cytosolic glycogen synthesis and breakdown are relatively well understood, recent findings relating to phagic glycogen degradation highlight a new area of investigation in the heart.