Changes in cardiac resistance to arrhythmogenic effects during ATP-dependent K+ channel activation

It has been found that pretreatment with ATP-dependent potassium channel (KATP-channel) opener, BMS 180448 (3 mg/kg, intravenously), increases cardiac resistance against arrhythmogenic action of coronary artery occlusion and reperfusion in anaesthetized rats. However, BMS 180448 induced a decrease in ventricular fibrillation threshold in rats postinfarction cardiac fibrosis. This effect was completely abolished by administration of the KATP-channel inhibitor, glibenclamide. By contrast, coadministration of BMS 180448 and selective sarcolemmal KATP-channel inhibitor, HMR 1098, promoted an increase in ventricular fibrillation threshold in rats with postinfarction cardiac fibrosis before normal value. The selective mitochondrial KATP-channel opener, diazoxide, also exacerbated a decrease in ventricular fibrillation threshold induced by postinfarction cardiac sclerosis. But after depletion of endogenous catecholamine storage by pretreatment with guanthidine, diazoxide, on the contrary, elevated the ventricular fibrillation threshold. It has been suggested that stimulation of mitochondrial ATP-sensitive potassium channels promotes an elevation in electrical stability of the heart, whereas opening of sarcolemmal KATP-channel increases a possibility of ventricular arrhythmias.