Mechanisms of Anoxic Tolerance and Metabolic Depression

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Dr. Jackson and his associates plan studies on mechanisms of acid-base, ionic, and metabolic regulation in reptiles and mammals. The reptile studies derive from past observations on the extraordinary anoxic tolerance of the freshwater turtle, Chrysemys picta bellii. Three directions will be pursued. First, the increase in plasma catecholamines (epinephrine and norepinephrine), that have been recenty observed when turtles are anoxic and/or acidotic, will be further documented and its functional significance and possible contribution to this animal's anoxic tolerance will be investigated. Second, the marked increase in plasma calcium concentration in turtles during anoxia leads us to a broad study of calcium kinetics and hormonal regulation of calcium metabolism in this species. He plans to compare the responses of the turtle to another reptile that lacks the turtle's mineral-rich shell. Third, because his recent results have failed to reveal a correlation between blood acidosis and anoxic tolerance or anaerobic metabolism he will investigate intracellular pH and metabolite control of selected tissues during various types of anoxic and acidotic conditions. The hypothesis presented in this project, that cellular acidosis depresses energy metabolism, relates to the final proposed project on the heterothermic bat, Eptesicus fuscus. Preliminary data suggest a dual pH control strategy in this species during torpor at 20 degrees centigrade: alphastat in the summer, pH- stat in the winter. The principal investigator's objective is to verify this observation in both blood and cells and evaluate its relevance to energy conservation of torpid bats. Overall, the goal is an understanding of the mechanisms regulating hypometabolic states.