Short episodes of ischemia (ischemic preconditioning) protect the heart against ventricular arrhythmias during zero-flow ischemia and reperfusion. However, in clinics, many episodes of ischemia present a residual flow (low-flow ischemia). Here we examined whether ischemic preconditioning protects against ventricular arrhythmias during and after a low-flow ischemia and, if so, by what mechanism(s).
Isolated rat hearts were subjected to 60 min of low-flow ischemia (12% residual coronary flow) followed by 60 min of reperfusion. Ischemic preconditioning was induced by two cycles of 5 min of zero-flow ischemia followed by 5 and 15 min of reperfusion, respectively. Arrhythmias were evaluated as numbers of ventricular premature beats (VPBs) as well as incidences of ventricular tachycardia (VT) and ventricular brillation (VF) during low-flow ischemia and reperfusion. Ischemic preconditioning significantly reduced the number of VPBs and the incidence of VT and of VF during low-flow ischemia. This antiarrhythmic effect of preconditioning was abolished by HOE 140 (100 nM), a bradykinin B2 receptor blocker. Similar to preconditioning, exogenous bradykinin (10 nM) reduced the number of VPBs and the incidence of VT and of VF during low-flow ischemia. Furthermore, the antiarrhythmic effects of both ischemic preconditioning and bradykinin were abolished by glibenclamide (1 μM), a non-specific blocker of ATP-sensitive K+ (KATP) channels. Finally, the antiarrhythmic effects of both ischemic preconditioning and bradykinin were abolished by HMR 1098 (10 μM), a sarcolemmal KATP channel blocker but not by 5-hydroxydecanoate (100 μM), a mitochondrial KATP channel blocker. In conclusion, ischemic preconditioning protects against ventricular arrhythmias induced by low-flow ischemia, and this protection involves activation of bradykinin B2 receptors and subsequent opening of sarcolemmal but not of mitochondrial KATP channels.