A comparison of transient outward currents in canine cardiac Purkinje cells and ventricular myocytes.
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 (I(to)) in single PCs from canine false tendons with midmyocardial ventricular myocytes (VMs). I(to) 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 I(to) but reversibly inhibited PC I(to) (IC(50) = 2.4 +/- 0.4 mM). PC I(to) was also more sensitive to 4-aminopyridine (IC(50) = 50 +/- 7 vs. 526 +/- 49 microM in VM, P < 0.0001). H(2)O(2) slowed I(to) inactivation in PCs but did not affect VM I(to). We conclude that PC I(to) shows significant differences from VM I(to), with some features, such as tetraethylammonium sensitivity, that have been reported in neither cardiac I(to) of atrial or ventricular myocytes nor cloned K(+) channel subunits (Kv1.4, Kv4.2, or Kv4.3) known to participate in cardiac I(to).
Department of Medicine and Research Center, Montreal Heart Institute, Montreal, Quebec H1T 1C8.
W
W
Han
Z
Z
Wang
S
S
Nattel
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D004285:Dogs; D004546:Elapid Venoms / Q000494:pharmacology; D004558:Electric Stimulation; D006321:Heart / Q000502:physiology*; D006325:Heart Atria; D006352:Heart Ventricles; D006861:Hydrogen Peroxide / Q000494:pharmacology; D009206:Myocardium / Q000166:cytology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011689:Purkinje Cells / Q000166:cytology / Q000502:physiology*; D019789:Tetraethylammonium / Q000494:pharmacology
D004546:Elapid Venoms; D015221:Potassium Channels; D019789:Tetraethylammonium; C020273:dendrotoxin; D006861:Hydrogen Peroxide; D015761:4-Aminopyridine