Failing energetics in failing hearts.

The perpetual and vigorous nature of heart muscle work requires efficient myocardial energetics. This depends not only on adequate ATP production, but also on efficient delivery of ATP to muscle ATPases and rapid removal of ADP and other by-products of ATP hydrolysis. Indeed, recent evidence indicates that defects in communication between ATP-producing and ATP-consuming cellular sites are a major factor contributing to energetic deficiency in heart failure. In particular, the failing myocardium is characterized by reduced catalytic activity of creatine kinase, adenylate kinase, carbonic anhydrase, and glycolytic enzymes, which collectively facilitate ATP delivery and promote removal of ADP, Pi, and H+ from cellular ATPases. Although energy transfer through adenylate kinase and glycolytic enzymes has been recognized as an adaptive mechanism supporting compromised muscle energetics, in the failing myocardium the total compensatory potential of these systems is diminished. A gradual accumulation of defects at various steps in myocardial energetic signaling, along with compromised compensatory mechanisms, precipitates failure of the whole cardiac energetic system, ultimately contributing to myocardial dysfunction. These advances in our understanding of the molecular bioenergetics in heart failure provide a new perspective toward improving the energetic balance of the failing myocardium.