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Am J Physiol Heart Circ Physiol 279: H466-H474, 2000;
0363-6135/00 $5.00
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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


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