Molecular mechanisms of defense against oxygen lack.

Evidence has been accumulating over the last several years suggesting that suppression of oxidative metabolism without concomitant glycolytic activation and the maintenance of cell membrane electrochemical gradients are central and minimal provisions for protecting tissues against oxygen lack. This evidence for diving vertebrates is reviewed and evaluated. It is concluded that the model explains long-term anoxia and hypoxia tolerance of aquatic lower vertebrates. Whereas this strategy, which is dominated by metabolic suppression capacities, may also be utilized by large, long-duration divers such as Weddell seals, it is unlikely to play a significant role in smaller and faster swimming marine mammals, where the energy demands of exercise greatly exceed the energy savings achievable by switching down metabolic rates of hypoperfused tissues.