³¹P Nuclear‐Magnetic‐Resonance Studies of Energy Metabolism in Tissue from the Marine Invertebrate Tapes watlingi

³¹P nuclear magnetic resonance spectra of tissue from the marine bivalve mollusc Tapes watlingi are presented. Spectra from foot muscle, adductor muscle and hearts contain resonances from the adenine nucleotides, inorganic phosphate and a phosphagen which is shown to be arginine phosphate. The intracellular pH of the tissue, measured from the chemical shift of the inorganic phosphate resonance, is 7.2, which is significantly lower than that of sea water, viz. 8.1. The importance of a correct choice of solution conditions for determining a correlation curve of chemical shift versus pH for tissue from marine organisms is emphasized. Spectra of perchloric acid extracts of muscle are used to determine levels of the major phosphorus‐containing metabolites in the tissue. The time courses of changes in the phosphorus‐containing metabolites of foot and adductor muscle are described. Under anaerobic conditions the sequence of events is similar to that observed in vertebrate skeletal muscle, but the overall rate of decay is much slower, e.g. arginine phosphate is present in foot muscle for almost 20 h at its physiological temperature. Oxygenation of the incubation medium prolongs the survival time of the tissue. Treatment with iodoacetamide and sodium azide under anaerobic conditions reduces the lifetime and changes the pattern of decay such that ATP begins to decay before the phosphagen is consumed, and most of the phosphate accumulates in sugar phosphates, mainly fructose 1,6‐biphosphate. The effect of low salinity stress is also examined. Spectra of muscle from animals exposed to 50% and 75% normal sea water for periods of about four weeks are essentially identical with those of normal animals. Furthermore, the decay of intact muscle incubated in 50% sea water is similar to that in normal sea water.