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Am J Physiol Heart Circ Physiol 279: H889-H900, 2000;
0363-6135/00 $5.00
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Vol. 279, Issue 3, H889-H900, September 2000

Aging-associated changes in whole cell K+ and L-type Ca2+ currents in rat ventricular myocytes

Shi J. Liu1,2, Richard P. Wyeth1,3, Russell B. Melchert1, and Richard H. Kennedy1,2

1 Department of Pharmaceutical Sciences, 2 Department of Pharmacology and Toxicology, and 3 Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205

The effect of aging on cardiac membrane currents remains unclear. This study examined the inward rectifier K+ current (IK1), the transient outward K+ current (Ito), and the L-type Ca2+ channel current (ICa,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 IK1 with a greater slope conductance but displayed smaller steady-state IK1. Aged myocytes also had a greater Ito with an increased rate of activation, but the Ito inactivation kinetics, steady-state inactivation, and responsiveness to L-phenylephrine, an alpha 1-adrenergic agonist, were unaltered. The magnitude of peak ICa,L in aged myocytes was decreased and accompanied by a slower inactivation, but the ICa,L steady-state inactivation was unaltered. Action potential duration in aged myocytes was prolonged only at 90% of full repolarization (APD90) when compared with the action potential duration of young adult myocytes. Aged myocytes from Long-Evans rats showed similar changes in Ito and ICa,L but an increased IK1. These results demonstrate aging-associated changes in action potential, in morphology, and in IK1, Ito, and ICa,L of rat ventricular myocytes that possibly contribute to the decreased cardiac function of aged hearts.

ion channels; action potential; patch clamp


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