Vol. 279, Issue 2, H466-H474, August 2000
A comparison of transient outward currents in canine cardiac
Purkinje cells and ventricular myocytes
Wei
Han1,3,
Zhiguo
Wang1,2, and
Stanley
Nattel1,2,3
1 Department of Medicine and Research Center, Montreal Heart
Institute, Montreal, Quebec H1T 1C8; 2 Department of
Medicine, University of Montreal, Montreal, Quebec H3C 3J7; and
3 Department of Pharmacology and Therapeutics, McGill
University, Montreal, Quebec, Canada H3G 1Y6
Although abnormalities in
Purkinje cell (PC) repolarization are important causes of cardiac
arrhythmias, the detailed properties of repolarizing currents in PCs
are incompletely understood. We compared transient outward
K+ current (Ito) in single PCs from
canine false tendons with midmyocardial ventricular myocytes (VMs).
Ito reactivation was biexponential, with a
similar rapid-phase time constant (30 ± 5 and 35 ± 4 ms for
VM and PC, respectively) but a large, slow component in PCs with a much
greater time constant than VM (1,427 ± 70 vs. 181 ± 24 ms,
P < 0.001). Tetraethylammonium had no effect on VM
Ito but reversibly inhibited PC
Ito (IC50 = 2.4 ± 0.4 mM). PC Ito was also more sensitive to
4-aminopyridine (IC50 = 50 ± 7 vs. 526 ± 49 µM in VM, P < 0.0001). H2O2
slowed Ito inactivation in PCs but did not
affect VM Ito. We conclude that PC
Ito shows significant differences from VM
Ito, with some features, such as
tetraethylammonium sensitivity, that have been reported in neither
cardiac Ito of atrial or ventricular myocytes
nor cloned K+ channel subunits (Kv1.4, Kv4.2, or Kv4.3)
known to participate in cardiac Ito.
potassium channels; molecular biology of cardiac ion channels; cardiac arrhythmias; action potentials; potassium channel blockers; antiarrhythmic drugs
