P-31 NUCLEAR-MAGNETIC-RESONANCE STUDY OF ENERGY-METABOLISM IN INTACT SLOW-TWITCH AND FAST-TWITCH MUSCLES OF RATS

The time course of the catabolism of phosphorylated metabolites was studied by phosphorus-31 NMR (P-31 NMR) spectroscopy over a 6-h period after the isolation of rat slow- and fast-twitch muscles, the soleus and the extensor digitorum longus (EDL), respectively, obtained without any muscle damage. In both muscles, rapid depletion of creatine phosphate was followed by a decrease in ATP. These high-energy phosphates disappeared earlier in the soleus than in the EDL. In both muscles, inorganic phosphate (Pi) largely increased in a biphasic pattern, and sugar phosphates (SP) also showed considerable increase. The NMR-visible total phosphates (NTP) increased significantly in the soleus during the latter stage of observation. This increase in NTP was attributed to an increase in Pi. Although the two muscles showed the same initial (7.21) and final (approximately 5.9) intracellular pH (pHi), the pattern of pHi decline differed between these muscles. The rapid fall of pHi in the soleus in the early stage suggests that nonlactic acid acidosis plays a significant role in postmortem changes.