Objective: Both K(ATP) channel opening drugs and ischaemic preconditioning have been suggested to protect the ischaemic heart by acting on K(ATP) channels in the inner mitochondrial membrane, uncoupling the proton gradient and partially dissipating the mitochondrial membrane potential. The aim of these studies was to use low concentrations of FCCP, a mitochondrial protonophore, to bypass the mitochondrial K(ATP) channel and partially uncouple the mitochondria and establish whether this activates protective pathways within the rat heart analogous to K(ATP) channel openers or preconditioning.
Methods: Isolated, Langendorff-perfused rat hearts were subjected to 25 min global zero-flow ischaemia and functional recovery assessed. Hearts were pretreated with FCCP (30-300 nM) in the presence or absence of glibenclamide (1 microM), 5-hydroxydecanoate (5-HD: 100 microM), N-acetyl cysteine (4 mM), or N-2-mercaptopropionyl glycine (1 mM). The metabolic consequences of FCCP perfusion in isolated hearts were studied using (31)P NMR, and reactive oxygen species (ROS) production was measured using DCF fluorescence in isolated rat ventricular myocytes.
Results: FCCP exerted a dose-dependent cardioprotective effect, with 100 nM FCCP being the optimal concentration. This effect could not be blocked by glibenclamide or 5-HD, but was completely attenuated by N-acetyl cysteine and N-2-mercaptopropionyl glycine. Perfusion with FCCP (100 nM) did not deplete bulk ATP during the pretreatment period but significantly depleted phosphocreatine. In ventricular myocytes, FCCP caused an antioxidant-sensitive increase in ROS production but diazoxide was without effect.
Conclusions: In the isolated rat heart, partial mitochondrial uncoupling with low-dose FCCP significantly improves post-ischaemic functional recovery via a ROS-dependent pathway. This cardioprotection is not mediated via the depletion of cellular ATP or mitochondrial K(ATP) channel activation.