Direct observation of the phosphate acceptor and phosphagen pool sizes in vivo

Earthworms were subjected to environmental anoxia (200 min) and electrical stimulation (5 min, 6 V, 50 Hz). The levels of high-energy phosphate compounds and the intracellular pH were monitored during anoxia, muscular contraction, and recovery by in vivo phosphorus-31 nuclear magnetic resonance (31P-NMR). Several key metabolites were determined by enzymatic analysis and reversed-phase high-performance liquid chromatography of perchlorate extracts. Because lombricine, the phosphagen phosphate acceptor of earthworms, is a phosphodiester, 31P-NMR permitted direct analysis of the extent of phosphorylation of the lombricine pool in vivo. Total lombricine, lombricine phosphate, ATP, and H+ were measured by NMR, and free ADP was calculated from the lombricine kinase equilibrium constant. The ADP concentration was not significantly changed by anoxia, but it rose threefold after stimulation. L-Lactate accumulated on stimulation, whereas multiple end products (L-lactate, alanine, succinate, and glutamine) were formed during environmental anaerobiosis.