Metabolic responses to freezing and anoxia by the periwinkle Littorina littorea

1. 1. The metabolic responses to freezing at −8°C for up to 72 h vs 72 h anoxia exposure under N2 gas at 5°C were compared in foot muscle of the intertidal gastropod, Littorina littorea. 2. 2. Freezing resulted in the accumulation of d-lactate and succinate (net increases of 1.1 and 3.9 μmol/g wet weight, respectively, compared with 5°C-acclimated controls) with an opposite decrease in the fermentative substrate, l-aspartate, whereas, by contrast, anoxia resulted in only a small, 0.5 μmol/gww, accumulation of d-lactate. 3. 3. Neither freezing nor anoxia exposure had a significant effect on muscle adenylate energy charge, suggesting that strong metabolic arrest mechanisms lowered energy demand to a level that could be met by fermentative metabolism alone. 4. 4. Activation of glycogenolysis was implied by elevated glucose-6-phosphate levels in muscle under both stresses but only during freezing did glucose accumulate (a net of 1.2 μmol/gww); changes in the levels of other glycolytic intermediates indicated regulatory control of glycolysis at pyruvate kinase under both stresses. 5. 5. No carbohydrate cryoprotectants were accumulated during freezing and neither stress changed the composition or size of the free amino acid pool (approx. 100 μmol/gww total amino acids composed of 77% taurine and 12% alanine). 6. 6. The data show that the metabolic responses to freezing and anoxia share some elements, indicating the importance of a good anaerobic capacity to freezing survival, but other aspects of metabolic response to freezing differ from anoxia and suggest factors that may be specifically important to cryoprotection.