Energy metabolism in the mantle muscle of the squid,Loligo pealeii

Abstract

1. The concentrations of glycolytic and Krebs cycle intermediates, α-glycerophosphate, the adenylates, and free amino acids were determined in the mantle muscle of the squid,Loligo pealeii, at rest and after 10 s of vigorous swimming. 2. Exercise resulted in significant increases in the levels of glucose-6-phosphate, fructose-1,6-diphosphate, and pyruvate. Phosphofructokinase and pyruvate kinase were identified as control points of glycolysis. In the Krebs cycle, changes in the levels of isocitrate and α-ketoglutarate suggested a facilitation of the isocitrate dehydrogenase reaction. 3. The products of anaerobic metabolism in mantle muscle, in particular α-glycerophosphate and octopine, did not accumulate during exercise indicating the aerobic nature of “burst” swimming in these animals. 4. Exercise resulted in a drop in muscle proline concentrations of approximately 2 μmol/g wet wt. which was accompanied by an almost stoichiometric increase in alanine levels. 5. The changes in adenylate concentrations with exercise were dramatic: ATP fell to 39% of the value in resting muscle while ADP and AMP rose 3- and 6-fold, respectively. Arginine phosphate concentrations fell from 10 μmol/g wet wt. in resting to 1 μmol/g wet wt. in exercised muscle. 6. Muscular work in this squid appears to be accompanied by an activation of aerobic carbohydrate metabolism, the α-glycerophosphate cycle functioning to maintain cytoplasmic redox balance. During metabolic activation, the carbon skeleton of proline may be used to augment the pool size of Krebs cycle intermediates. The observed changes in arginine phosphate and AMP levels could be key in the activation of the reactions of glycolysis.