EXERCISE AND RECOVERY IN FROG-MUSCLE - METABOLISM OF PCR, ADENINE-NUCLEOTIDES, AND RELATED-COMPOUNDS

The effects of exercise (swimming), fatigue, and recovery on the intra cellular pH (pH(i)), energy-rich phosphates, and related metabolites w ere studied in the gastrocnemius muscle of common frogs (Rana temporar ia) at 20 degrees C. Exercise caused a rapid decrease in the content o f phosphocreatine (PCr) and a corresponding increase in that of P-i. T he ATP level remained virtually constant for 1 min; its precipitous de crease during the following minute was associated with a rise in the c ontents of inosine 5'-monophosphate (IMP) and NH4+ indicating a marked activation of AMP deaminase. Five minutes of swimming caused severe f atigue, which was correlated with decreases in muscle PCr (-85%), ATP (-42%), and pH(i) (-0.8 units). Recovery appeared almost complete with in 2 h, and the frogs were then induced to swim again. During the init ial 10 s of this second exercise, ATP synthesis was as high as in the first exercise, but the rate decreased more rapidly between 10 and 60 s, thus indicating that repeated exercise caused increased metabolic s tress. IMP formation in working muscle was not strictly correlated wit h the pH(i) or the tissue contents of P-i, AMP, and ADP, although from studies in vitro AMP deaminase is known to be modulated by these para meters.