Flumazenil preconditions cardiomyocytes via oxygen radicals and K(ATP) channels

We determined whether flumazenil mimics ischemic preconditioning in chick cardiomyocytes and examined the role of intracellular reactive oxygen species (ROS) and ATP-dependent potassium (K(ATP)) channels in mediating the effect. Chick ventricular myocytes were perfused with a balanced salt solution in a flow-through chamber. Cell viability was quantified using propidium iodide, and ROS generation was assessed using the reduced form of 2',7'-dichlorofluorescin (DCFH). Cells were exposed to 1 h of simulated ischemia and 3 h of reoxygenation. Preconditioning was initiated with 10 min of ischemia followed by 10 min of reoxygenation. Alternatively, flumazenil was added to the perfusate for 10 min and removed 10 min before the start of ischemia. Flumazenil (1 and 10 microM) and preconditioning reduced cell death [54 +/- 5%, n = 3; 26 +/- 4%, n = 6 (P < 0.05); and 20 +/- 2%, n = 6 (P < 0.05), respectively, vs. 57 +/- 7%, n = 10, in controls] and increased DCFH oxidation (an index of ROS production) [0.35 +/- 0.11, n = 3; 2.64 +/- 0.69, n = 8 (P < 0.05); and 2.46 +/- 0.52, n = 6 (P < 0.05), respectively, vs. 0.26 +/- 0.05, n = 9, in controls]. Protection and increased ROS signals with flumazenil (10 microM) were abolished with the thiol reductant N-(2-mercaptopropionyl)-glycine (2-MPG, 800 microM), an antioxidant (cell death: 2-MPG + flumazenil, 55 +/- 12%, n = 6; ROS signals: 2-MPG + flumazenil, 0.11 +/- 0.19, n = 6). Treatment with 5-hydroxydecanoate (1 mM), a selective mitochondrial K(ATP) channel antagonist, abolished its protection. These results demonstrate that flumazenil mimics preconditioning to reduce cell death in myocytes. ROS signals with the resultant mitochondrial K(ATP) channel activation are important components of the intracellular signaling pathway of flumazenil.