Synchronized Whole Cell Oscillations in Mitochondrial Metabolism Triggered by a Local Release of Reactive Oxygen Species in Cardiac Myocytes

Reactive oxygen species (ROS) and/or Ca²⁺ overload can trigger depolarization of mitochondrial inner membrane potential (ΔΨ _m) and cell injury. Little is known about how loss of ΔΨ_m in a small number of mitochondria might influence the overall function of the cell. Here we employ the narrow focal excitation volume of the two-photon microscope to examine the effect of local mitochondrial depolarization in guinea pig ventricular myocytes. Remarkably, a single local laser flash triggered synchronized and self-sustained oscillations in ΔΨ_m, NADH, and ROS after a delay of ∼40s, in more than 70% of the mitochondrial population. Oscillations were initiated only after a specific threshold level of mitochondrially produced ROS was exceeded, and did not involve the classical permeability transition pore or intracellular Ca ²⁺ overload. The synchronized transitions were abolished by several respiratory inhibitors or a superoxide dismutase mimetic. Anion channel inhibitors potentiated matrix ROS accumulation in the flashed region, but blocked propagation to the rest of the myocyte, suggesting that an inner membrane, superoxide-permeable, anion channel opens in response to free radicals. The transitions in mitochondrial energetics were tightly coupled to activation of sarcolemmal K_ATP currents, causing oscillations in action potential duration, and thus might contribute to catastrophic arrhythmias during ischemia-reperfusion injury.