Carbohydrate metabolism during anoxia and post-anoxia recovery in Chasmagnathus granulata crabs maintained on high-protein or carbohydrate-rich diets

Abstract

We assessed the effects of anoxia exposure and recovery on glycogen synthesis and mobilization, glucose uptake, and on the enzymes that control carbohydrate metabolism in the hepatopancreas of Chasmagnathusgranulata crabs receiving either a carbohydrate-rich (HC) or a high-protein diet (HP). In both dietary groups, anoxia led to a reduction in glucose uptake and in glycogen synthesis, and to an increase in hepatopancreas glycogen mobilization and in hemolymph glucose concentration. During the first 4 h of exposure to anoxia, total glycogen phosphorylase (GPT) and a form activity increased in HP and HC crabs, leading to a decrease in hepatopancreas glycogen concentration. During recovery, HP and HC crabs rapidly restored the hemolymph glucose levels to pre-anoxia concentrations. In HC crabs, incorporation of 14C from glucose into glycogen increased gradually after 12 h in normoxia, leading to restoration of glycogen concentration. Also during recovery, the ratio of glycogen synthase I (GSI) to glycogen phosphorylase a (GPa) increased in the HC group. In turn, recovering HP crabs had two peaks of glycogen synthesis, related with two peaks in the ratio of GSI to GPa. Consequently, no mobilization of 14C-glycogen occurred in recovering HP animals. Anoxia in C.granulata induces a marked decrease in the synthesis of carbohydrate reserves that is accompanied by an increase in glycogen mobilization and in circulating glucose levels. During the recovery period, there is an activation of endergonic processes which cause a decrease in hemolymph glucose levels. In C.granulata, glycogen metabolism seems to be controlled by the ratio of the GSI form to the GPa form. In field conditions, theses changes in the metabolic pattern may result from environmental PO2 availability. In the winter, C.granulata stays in its holes, where environmental PO2 falls to zero. The carbohydrate or protein content of the diets administrated to the crabs seem to induce different metabolic adjustments during anoxia and recovery.