Metabolic Responses of the Estuarine Gastropod Thais Haemastoma to Hypoxia (Energy Charge, Opine Dehydrogenase,survival, Adaptation, Respiration).

The hypoxia tolerance (LC-50) of Thais haemastoma was inversely related to acclimation temperature but was not related to acclimation salinity between 10 and 30(DEGREES)C and 10 and 30(\u27o)/ooS. T. haemastoma is moderately tolerant to anoxia, the LT-50 (time to 50% mortality) being 12-22 days. Oxyregulatory ability varies from poor to good, and varies inversely with temperature. The oxygen consumption rate was lower after 28 days exposure to hypoxic conditions than at full oxygen saturation at all salinities at 20 and 30(DEGREES)C. Oxygen consumption was low at 10(DEGREES)C regardless of ambient PO(,2). Oxyregulatory ability in T. haemastoma did not show acclimation after 28 days exposure to 53 mm O(,2) at 30(DEGREES) and 30(\u27o)/ooS. Likewise, no induction of the activities of the pyruvate oxidoreductase enzymes in foot tissue occurred after 28 days exposure to 10, 33, and 67% of oxygen saturation. The ratio of mean activities of alanopine dehydrogenase:lactate dehydrogenase:strombine dehydrogenase:octopine dehydrogenase was 3.8:1.2:1.0:0. Alanopine dehydrogenase activity nearly doubled on the first day but had returned to the control level by day 2, and no change occurred in strombine dehydrogenase and lactate dehydrogenase activity over 6 days exposure to anoxia. The total concentration of cellular adenylates remained constant, but the adenylate energy charge, ( ATP + .5 ADP )/( ATP + ADP + AMP ), was reduced at low PO(,2)\u27s. Arginine phosphate concentrations were lower in snails exposed to 10 and 33% oxygen saturation than in those at 67 and 100% of oxygen saturation. Energy charge declined from 0.79 to 0.58 after one day of anoxia at 30(DEGREES)C and 30(\u27o)/ooS while the arginine phosphate concentration declined by 95%. There was no further decrease in either variable with longer exposure to anoxia. Hypoxia tolerance of T. haemastoma is due to a reduction in metabolic demand, especially at low temperature, with ATP production maintained at the expense of arginine phosphate while metabolism switches to anaerobic pathways. The opine pathway is probably only used as a transitional mode before use of long-term anaerobic pathways is initiated