METABOLIC RESPONSES TO ANOXIA AND FREEZING BY THE FREEZE-TOLERANT MARINE MUSSEL GEUKENSIA-DEMISSUS

The effects of 2 or 12 h freezing at -6 degrees C or anoxia exposure a t 5 degrees C on the metabolic responses of gill, mantle, adductor mus cle, and hepatopancreas were characterized in the freeze tolerant, int ertidal ribbed mussel Geukensia demissus (Dillwyn). In general, freezi ng and anoxia elicited different metabolic responses and these also di ffered in a tissue-specific manner. Fermentative end products accumula ted in all tissues except gill under both stresses. In adductor muscle , lactate was produced in both cases. In mantle and hepatopancreas, on ly succinate accumulated in anoxia, correlated with an opposite decrea se in aspartate, and changes in glycolytic intermediates were consiste nt with anoxia-induced metabolic arrest. During freezing, however, bot h lactate and succinate accumulated (as well as alanine in hepatopancr eas) with net end product accumulation 3-4-fold greater than during an oxia and changes in glycolytic intermediates were consistent with the derivation of these products from carbohydrate catabolism. Other diffe rences in response to freezing versus anoxia included the accumulation of glucose in all tissues and a reduction of energy charge in mantle during freezing, but not in anoxia. Taurine and glycine comprised abou t 80-85% of the total free amino acid pools in all tissues; in gill le vels of both amino acids fell significantly during freezing or anoxia exposures whereas in mantle a significant decrease in these amino acid s occurred during anoxia only. The data show both a broader range of m etabolic responses, and greater net changes in metabolite levels durin g freezing compared with anoxia. This suggests (1) that metabolic resp onses to freezing include both cryoprotective and ischemia-protective changes, and (2) that tissue mechanisms of metabolic rate depression a re rapidly induced during anoxia exposure but develop more slowly duri ng freezing.