TY - JOUR T1 - Properties of a Time-Dependent Potassium Current in Pig Atrium: Evidence for a Role of K<sub>v</sub>1.5 in Repolarization JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 898 LP - 906 DO - 10.1124/jpet.106.110080 VL - 319 IS - 2 AU - Joachim R. Ehrlich AU - Christin Hoche AU - Pierre Coutu AU - Christiane Metz-Weidmann AU - Werner Dittrich AU - Stefan H. Hohnloser AU - Stanley Nattel AU - Heinz Gögelein Y1 - 2006/11/01 UR - http://jpet.aspetjournals.org/content/319/2/898.abstract N2 - Cardiac electrical activity is modulated by potassium currents. Pigs have been used for antiarrhythmic drug testing, but only sparse data exist regarding porcine atrial ionic electrophysiology. Here, we used electrophysiological, molecular, and pharmacological tools to characterize a prominent porcine outward K+ current (IK,PO) in atrial cardiomyocytes isolated from adult pigs. IK,PO activated rapidly (time to peak at +60 mV; 2.1 ± 0.2 ms), inactivated slowly (τf = 45 ± 10; τs = 215 ± 28 ms), and showed very slow recovery (τf = 1.54 ± 0.73 s; τs = 7.91 ± 1.78 s; n = 9; 36°C). Activation and inactivation were voltage-dependent, and current properties were consistent with predominant K+ conductance. Neurotoxins (heteropodatoxin, hongatoxin, and blood depressing substance) that block Kv4.x, Kv1.1, -1.2, -1.3, and -3.4 in a highly selective manner as well as H2O2 and tetraethylammonium, did not affect the current. Drugs with Kv1.5-blocking properties (flecainide, perhexiline, and the novel atrial-selective antiarrhythmic 2′-{2-(4-methoxyphenyl)-acetylamino-methyl}-biphenyl-2-carboxylic acid (2-pyridin-3-yl-ethyl)-amide; AVE0118) inhibited IK,PO (IC50 of 132 ± 47, 17 ± 10, and 1.25 ± 0.62 μM, respectively). 4-Aminopyridine suppressed the current and accelerated its decay, reducing charge carriage with an IC50 of 39 ± 15 μM. Porcine-specific Kv channel subunit sequences were cloned to permit real-time quantitative reverse transcription-polymerase chain reaction on RNA extracted from isolated cardiomyocytes, which showed much greater abundance of Kv1.5 mRNA compared with Kv1.4, Kv4.2, and Kv4.3. Action potential recordings showed that IK,PO inhibition with 0.1 mM 4-AP delayed repolarization (e.g., action potential duration at –50 mV increased from 45 ± 9 to 69 ± 5 ms at 3 Hz; P &lt; 0.05). In conclusion, porcine atrium displays a current that is involved in repolarization, inactivates more slowly than classic transient outward current, is associated with strong Kv1.5 expression, and shows a pharmacological profile typical of Kv1.5-dependent currents. The American Society for Pharmacology and Experimental Therapeutics ER -