© 2003 by European Society of Cardiology
Copyright © 2003, European Society of Cardiology
Calcium and potassium currents in cells from adult and aged canine right atria
Departments of Pharmacology and Pediatrics, Center for Molecular Therapeutics, Columbia University, New York, NY 10032, USA
pab4{at}columbia.edu
* Corresponding author. Present address: Department of Pharmacology, Columbia College of Physicians and Surgeons, 630 West 168th St., New York, NY 10032, USA. Tel.: +1-212-305-7907; fax: +1-212-305-0529.
Background: Action potential (AP) contours vary considerably between normal adult and aged right atrial fibers. The ionic bases for these differences remain unknown. Therefore we studied Ca2+ and K+ currents in cells from adult and aged canine right atria (RA). Methods and Results: We used whole cell patch clamp recording techniques to measure L-type Ca2+ currents (ICaL) with either Ca2+ or Ba2+ (3 mM) as the charge carrier, and both the transient outward (Ito) and sustained potassium currents (Isus) in cells dispersed from normal adult (Adult, 2–5 years) and older dogs (Aged, >8 years). There is a significant reduction in peak ICaL (47%) and IBaL (43%) in Aged cells, yet differences in IBaL disappear with maximal β adrenergic stimulation (isoproterenol, 1 µM). Composite Ito and Isus densities were significantly increased in the Aged versus Adult cell group (by 31 and 27% at +50 mV, respectively). Ito decay during a maintained depolarization was slowed in Aged cells. Furthermore, Ito steady-state inactivation curve was shifted positively in Aged cells. Finally, composite Ito and Isus currents of Aged cells were more sensitive to tetraethylammonium chloride (TEA), a specific inhibitor of some types of K+ currents. In the presence of TEA (5 mM), Ito in Aged cells was significantly greater than that in Adult cells. Conclusions: Ionic currents differ in Aged versus Adult right atrial cells, such that a reduced Ca2+ current and augmented outward currents could contribute significantly to the altered AP contour of the Aged RA cell. Adrenergic stimulation appears to restore Ba2+ currents in Aged cells. Finally, an augmented TEA sensitive current plays a role in changes of Isus in Aged right atrial cells.
KEYWORDS Atria; Calcium current; Potassium currents; Cellular electrophysiology
1 These authors contributed equally to this work.
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