EFFECTS OF AGING ON NA-PUMP CURRENT IN RAT VENTRICULAR MYOCYTES()

This study was designed to determine if aging affects ouabain-sensitiv e Na+-pump current (I-p), an electrophysiological measure oi Na,K-ATPa se activity, in rat heart. Ventricular myocytes were enzymatically iso lated from hearts of young adult (4-6 months of age) and aged (28-36 m onths of age) male Long-Evans rats. I-p was monitored using convention al whole-cell patch-clamp techniques under both maximally stimulating (85 mM intracellular Na+ with 10.8 mM extracellular K+) and 'physiolog ical' (10 mM intracellular Na+ with 5.4 mM extracellular K+) condition s. Values were expressed relative to membrane capacitance to account f or the larger cell size of the aged myocytes. Results indicated that m aximal I-p 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 I-p nor the p ump current monitored under 'physiological' conditions were affected b y 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.