Exercise and recovery in frog muscle: metabolism of PCr, adenine nucleotides, and related compounds

The effects of exercise (swimming), fatigue, and recovery on the intracellular pH (pHi), energy-rich phosphates, and related metabolites were studied in the gastrocnemius muscle of common frogs (Rana temporaria) at 20 degrees C. Exercise caused a rapid decrease in the content of phosphocreatine (PCr) and a corresponding increase in that of Pi. The ATP level remained virtually constant for 1 min; its precipitous decrease during the following minute was associated with a rise in the contents of inosine 5'-monophosphate (IMP) and NH4+, indicating a marked activation of AMP deaminase. Five minutes of swimming caused severe fatigue, which was correlated with decreases in muscle PCr (-85%), ATP …

Control of glycolysis in vertebrate skeletal muscle during exercise

The gastrocnemius muscle of the frog (Rana temporaria) has a high capacity for anaerobic glycolysis from glycogen. Glycolytic metabolites and effectors of phosphofructokinase, particularly the hexose bisphosphates, were followed in muscle during exercise (swimming between 5 s and 5 min), recovery (rest for up to 2 h after 5 min of swimming), and repeated exercise (swimming for up to 60 s after 2 h of recovery). Glycogen phosphorylase and phosphofructokinase were swiftly activated with exercise. The hexose bisphosphates followed markedly different time courses. Fructose 1,6-bisphosphate was transiently increased in both exercise and repeated exercise. This appears to be an effect rather tha…

Oxygen Availability, Energy Metabolism, and Metabolic Rate in Invertebrates and Vertebrates

It has often been emphasized that primitive life originated in an environment devoid of oxygen. The first eukaryotic cells, however, appeared some 1.4 billion years ago when the earth’s atmosphere had already turned from a mildly reducing to an oxidizing one by the photosynthetic action of prokaryotes that used H20 as reducing agent (see Harold 1986, for review). The presence of free oxygen obviously was a major force shaping the evolution of eukaryotic cells. As a consequence all animals are primarily aerobes, using respiratory chains with oxygen as electron acceptor (oxidant) and membrane-bound ATP synthases for the production of ATP.

Adenine nucleotide metabolism during anoxia and postanoxic recovery in insects

Severe hypoxia (anoxia), if maintained for more than a few minutes, causes irreversible damage in humans and other mammals. Why mammals are so vulnerable to anoxia is not fully understood. It is therefore of interest to study animals that are more tolerant of anoxia in order to identify physiological and metabolic properties that are correlated with a high tolerance of anoxia. Insects have high metabolic rates and their energy metabolism is dependent on aerobic ATP production. In insects, as in mammals, anoxia causes a rapid breakdown of physiological function, resulting in a state similar to rigor mortis. This is accompanied by a precipitous decrease in metabolic rate. In contrast to mamma…

Brains burning fat: Different forms of energy metabolism in the CNS of insects