Mitochondria in active epibenthic ectotherms ? ROS consumers instead of producers?Abele#, D., Philipp#, E., Heise#, K., Keller#, M., Pörtner#, H.O., Nikinma*, M.#Dept. Marine Ecophysiol. Ecotoxicol., Alfred-Wegener Institute f. Polar-& Marine Res., Bremerhaven, Germany; *Dept. of Biology, University of Turku, FinlandMitochondria have been described as the major cellular ROS producers, especially under physiological stress. Whereas we were able to detect a net production of ROS in mitochondria isolated from metabolically low tuned infaunal marine bivalves and worms, ROS release from mitochondria, isolated from more active or higher evolved epibenthic animals, scallops and benthic fish, was null under all experimental conditions. Due to considerable antioxidant potential in the matrix, these mitochondria actually seem to prevent ROS release into the cell during routine activity. Higher mitochondrial volume densities and subsarcolemnal localization found in many active polar swimmers, may hence not only decrease diffusion distances of oxygen inside the cells, but help to control the local dioxygen concentration and even mop up extra-mitochondrially produced ROS in the cell periphery, preventing initiation of lipid radical chain reactions.A control of extra-mitochondrial ROS levels could be important to enable onset of stress signalling. In animals, many forms of stress converge into a state of functional hypoxia. We found first evidence that hypoxia inducible transcription factor HIF may be involved in metabolic re-organisation during heat and cold stress in polar and North Sea fish.