We used fluorescent probes and EPR to study the mechanism (s) underlying reactive
oxygen species (ROS) production by endothelial cell mitochondria and the action of
mitoquinol, a mitochondria-targeted antioxidant. ROS measured by fluorescence resulted
from complex I superoxide released to the matrix and converted to H 2 O 2. In contrast, EPR
largely detected superoxide generated at complex III and effluxed outward. ROS
fluorescence by mitochondria fueled by the complex II substrate, succinate, was substantial …