Energy metabolism in the foot of the marine gastropod Nassa mutabilis during environmental and functional anaerobiosis

Abstract

This study concerns the effects of oxygen deprivation due to incubation in oxygen free sea water (environmental anoxia) or exercise (functional anoxia) and of exposure to air on the mode of energy production in the foot of the whelk Nassa mutabilis. Additionally, energy metabolism of the foot muscle was investigated during exercise after different anoxia periods and during the subsequent recovery period. During environmental anoxia, phosphoarginine, glycogen and aspartate are broken down as substrates and alanine and succinate are formed as products. There was no production of D-lactate or octopine. The energy charge value fell after 24-h anoxia. Exposure to air resulted in only small changes in phosphoarginine and alanine levels, suggesting that oxygen uptake was impaired in the first phase of air exposure but that, later, aerial respiration kept pace with the energy demand. Exercise caused a dramatic decrease of phosphoarginine concentration, coupled with glycolytic ATP production via octopine formation. In the recovery period (after exercise), the level of phosphoarginine was rapidly restored. An anaerobic component was evident during recovery as shown by the accumulation of D-lactate. Thus, both terminal dehydrogenases, octopine- and lactate dehydrogenase, are active in the muscle, but under different physiological conditions. Octopine formation also took place when the whelks were subjected to exercise after 4 or 24 h of anoxia. In this case, glycolysis provided between 70 and 90% of the energy required since the phosphagen store had already been depleted during the anoxic period. When the work load was increased (greater number of leaps), it became evident that the action of arginine kinase and octopine dehydrogenase are not closely linked. First there was an increase of arginine and then later a condensation of arginine with pyruvate to form octopine.