Energy Production in the Muscle Tissues of Different Kinds of Molluscs

Abstract

The main sources of energy for muscular contraction are phosphoarginine and carbohydrate. Phosphoarginine is important in the generation of both high (burst mechanical activity) and low (anoxia-survival) rates of energy production. Aerobic catabolism powers muscles which contract slowly and regularly over long periods of time whereas anaerobic catabolism powers muscles which contract vigorously during burst mechanical activity (cephalopods) and muscles deprived of oxygen. Three types of anaerobic pathway (succinate, opine and lactate) are employed which differ in their energetic characteristics. The succinate pathway is a high (relatively) efficiency/low rate of energy production pathway used in anoxia-survival. The opine and lactate pathways are low efficiency pathways concerned with maintaining or increasing rates of energy production. The octopine pathway produces the highest rates of energy production but in some situations the rates are similar to other opine pathways, viz. octopine and strombine pathways during the recovery periods of respectively the scallop P. magellanicus and the mussel M. edulis. The lactate pathway is used in terrestrial and freshwater gastropods and in bivalves whose normal requirement for anaerobic metabolism is low i.e. freshwater and aerial-respiring species. Past evolutionary pressures were possibly responsible for the selection of the octopine pathway in the Mollusca.