Phosphorus Nuclear Magnetic Resonance Studies of Energy Metabolism in Molluscan Tissues: Intracellular pH Change and the Qualitative Nature of Anaerobic End Products

Phosphorus nuclear magnetic resonance (31P-NMR) techniques were used to investigate anaerobic energy metabolism in the ventricle of the whelk Busycon contrarium. Under anoxic perfusion conditions, in the absence or presence of 3-mercaptopicolinate (MPA), an inhibitor of phosphoenolpyruvate carboxykinase, there was a utilization of aspartate leading to the accumulation of succinate and alanine. In the presence of amino-oxyacetate (AOA), a transaminase inhibitor, aspartate utilization and alanine formation were blocked. In contrast, the glycolytic production of octopine, glycerol-3-phosphate, and D-lactate was greatly enhanced. Overall rates of ATP turnover were virtually the same in control, MPA, and AOA treatments. Rates of anoxic proton accumulation in the three experimental treatments were not significantly different. This similarity in degree of intracellular acidification during anoxia is noteworthy in that the pattern of end product accumulation in the AOA experiments differed radically from those in the other two treatments. Thus, under these experimental conditions, the extent of intracellular pH change appeared to be independent of the qualitative nature of the end product. Using the approach of Pörtner and colleagues and taking into account the distinct pattern of aspartate fermentation in B. contrarium ventricle, we estimated that proton yields of the chemical transformations in the control and MPA treatments were insufficient to account for the observed reduction in intracellular pH (pHi). It is possible that there were proton-yielding processes other than glycolysis that were overlookedin this analysis. Alternatively, the above results might be a manifestation of a downward regulation of pHi as a central adaptive response to anoxia.