Aging-associated changes in whole cell K super(+) and L-type Ca super(2+) currents in rat ventricular myocytes

• Published in: American journal of physiology. Heart and circulatory physiology Vol. 279; no. 3; pp. H889 - H900
• Main Authors: Liu, S J, Wyeth, R P, Melchert, R B, Kennedy, R H
• Format: Journal Article
• Language: English
• Published: 01.09.2000
• ISSN: 0363-6135

The effect of aging on cardiac membrane currents remains unclear. This study examined the inward rectifier K super(+) current (I sub(K1)), the transient outward K super(+) current (I sub(to)), and the L-type Ca super(2+) channel current (I sub(Ca,L)) in ventricular myocytes isolated from young adult (6 mo) and aged (>27 mo) Fischer 344 rats using whole cell patch-clamp techniques. Along with an increase in the cell size and membrane capacitance, aged myocytes had the same magnitude of peak I sub(K1) with a greater slope conductance but displayed smaller steady-state I sub(K1). Aged myocytes also had a greater I sub(to) with an increased rate of activation, but the I sub(to) inactivation kinetics, steady-state inactivation, and responsiveness to L-phenylephrine, an alpha sub(1)-adrenergic agonist, were unaltered. The magnitude of peak I sub(Ca,L) in aged myocytes was decreased and accompanied by a slower inactivation, but the I sub(Ca,L) steady-state inactivation was unaltered. Action potential duration in aged myocytes was prolonged only at 90% of full repolarization (APD sub(90)) when compared with the action potential duration of young adult myocytes. Aged myocytes from Long-Evans rats showed similar changes in I sub(to) and I sub(Ca,L) but an increased I sub(K1). These results demonstrate aging-associated changes in action potential, in morphology, and in I sub(K1),I sub(to), and I sub(Ca,L) of rat ventricular myocytes that possibly contribute to the decreased cardiac function of aged hearts.