Organ-specific control of glycolysis in anoxic turtles
Control of glycolysis during anoxia was investigated in five organs (heart, brain, liver, and red and white skeletal muscles) of the freshwater turtle, Pseudemys scripta, after 1 or 5 h of submergence in N2-bubbled water. Lactate was produced as the metabolic end product, with distinct organ differences in the amount (net lactate accumulation was 2.4-fold higher in brain than white muscle) and rate (lactate production in liver dropped 16-fold after the 1st h) of lactate accumulation. ATP and total adenylate contents of all organs were reduced (by 15-32%) after 1 h of submergence, but energy charge was maintained, after 5 h, adenylate contents had fully recovered. Changes in the levels of hexose and triose phosphate intermediates of glycolysis indicated an activation of glycolysis within the 1st h of anoxia exposure in brain, heart, and skeletal muscles. By 5 h, however, these were reversed, and a glycolytic rate depression was indicated, consistent with the overall metabolic rate depression accompanying long-term anaerobiosis in the turtle. Crossover analysis indicated glycolytic control at the pyruvate kinase reaction in all organs during both glycolytic activation and metabolic depression; regulatory control at the phosphofructokinase locus was primarily important only during glycolytic activation in heart and red muscle. The same analysis indicated a very rapid glycolytic inhibition in liver occurring within the 1st h of anoxia exposure; this allows glycogenolysis to be directed toward glucose export yielding the fermentative fuel used by other organs during anoxia.