Effects of aging on Na(+)-pump current in rat ventricular myocytes

This study was designed to determine if aging affects ouabain-sensitive Na(+)-pump current (Ip), an electrophysiological measure of Na,K-ATPase activity, in rat heart. Ventricular myocytes were enzymatically isolated from hearts of young adult (4-6 months of age) and aged (28-36 months of age) male Long-Evans rats. Ip was monitored using conventional whole-cell patch-clamp techniques under both maximally stimulating (85 mM intracellular Na+ with 10.8 mM extracellular K+) and 'physiological' (10 mM intracellular Na+ with 5.4 mM extracellular K+) conditions. Values were expressed relative to membrane capacitance to account for the larger cell size of the aged myocytes. Results indicated that maximal Ip is smaller (e.g. approximately 23% at the holding potential of -40 mV) in myocytes isolated from aged as compared to young adult rats. However, neither the voltage-dependence of maximal Ip nor the pump current monitored under 'physiological' conditions were affected by age in general, these data support results of previous biochemical and ion flux studies which demonstrated that aging is associated with a decline in the Na(+)-pump capacity of the myocardium.