Electro-mechanical coupling in the aging heart: role of the Late Na+ current

The aging myopathy manifests itself with diastolic dysfunction and preserved ejection fraction. However, the difficulty in defining myocardial aging and the mechanisms involved complicates the recognition of the cellular processes underlying impaired diastolic relaxation. We raised the possibility that, in a mouse model of physiological aging, defects in the electromechanical properties of cardiomyocytes are important determinants of the diastolic properties of the myocardium, independently from changes in the structural composition of the muscle and collagen framework. Here we show that an increase in the late Na+ current (INaL) in aging cardiomyocytes prolongs the action potential (AP) and influences the temporal kinetics of Ca2+ cycling and cell shortening. These alterations increase force development and passive tension. Inhibition of INaL shortens the AP and corrects the dynamics of Ca2+ transient, cell contraction and relaxation. Similarly, repolarization and diastolic tension of the senescent myocardium are partly restored. INaL offers inotropic support, but negatively interferes with cellular and ventricular compliance, providing a new perspective of the biology of myocardial aging and the etiology of the defective cardiac performance in the elderly.