Over-expression of Kv1.5 in rat cardiomyocytes extremely shortens the duration of the action potential and causes rapid excitation

Background: Genetically abnormal action potential duration (APD) can be a cause of arrhythmias that include long and short QT interval syndrome. Purpose: The aim of this study was to evaluate the arrhythmogenic effect of short QT syndrome induced by the over-expression of Kv1.5 in rat. Methods: From Sprague-Dawley rats on fetal days 18-19, cardiomyocytes were excised and cultured with and without transfection with the Kv-1.5 gene using an adenovirus vector. The expression of Kv1.5 was proven by immunohistochemistry and Western blot analysis. In the culture dish and in the whole cells, the electrical activities were recorded using the whole-cell patch-clamp technique and the effects of 4-AP and verapamil were tested., Results: After transfection with Kvl.5 for 12 h, immunohistochemical staining and Western blot analysis were positive for Kvl.5 while they were negative in the control transfected with only Lac-Z. In the culture dish, the myocytes showed spontaneous beating at 115 beats/min (bpm) just prior to the transfection with Kvl.5 and increased to 367 bpm at 24 h. The control myocytes showed stable beating rates during culturing. 4-AP at 200 mu M slowed down the rate and verapamil abolished the beating. In the whole cells, the maximal resting membrane potential was slightly depolarized and APD was extremely abbreviated both at 50% and 90% of repolarization compared with those of the control. Rapid spontaneous activities were found in a single myocyte with Kv1.5 transfection and 4-AP slowed down the frequency of the activities with a reversal of the shortened APD. Conclusion: The over-expression of Kv1.5 induced short APD and triggered activities in rat cardiomyocytes. This model can be used to study the arrhythmogenic substrate of short QT syndrome. (c) 2006 Elsevier Inc. All rights reserved.