Most metozoans are aerobic organisms that die when denied adequate supplies of molecular oxygen. However, euryoxic animals, as intertidal invertebrates like the bivalve Mytilus edulis, tolerate prolonged periods of hypoxia, or alternating hypoxia and normoxia, with few apparent difficulties. Behavioral, physiological and biochemical responses of aquatic invertebrates to anoxia and hypoxia have been extensively studied. Major mechanisms whereby euryoxic invertebrates survive prolonged lack of oxygen have been elucidated. This project will examine the recovery of aerobic conditions from environmental and functional anoxia and hypoxia. The recovery to aerobic conditions from anaerobic states of tissues is important since recent experiments have demonstrated that a lack of energy production per se may not be the proximate cause of death in aerobic organisms. For instance, in mammals myocardium (heart tissue) and bowel, two tissues especially prone to damage upon exposure to cycles of anoxia and normoxia, show little histologic evidence of cell injury or death on exposure to anoxia, even though ischemia persists for over 60 minutes. However, when molecular oxygen is introduced to the tissue during reperfusion, cellular structures begin to reveal degeneration typical of moribund tissue. This research proposal will deal with the role of superoxide radicals, generated during reperfusion, in reoxygenation injury. Many intertidal invertebrates thrive on alternating periods of hypoxia when the tide ebbs and normoxia when the tide returns. Stenoxic subtidal species suffer from similar conditions of alternating hypoxia-normoxia. Euryoxic intertidal and stenoxic subtidal species will be compared to examine resistance and susceptibility to events underlying reperfusion injury. This RUI proposal will involve research by three undergraduates each summer.
