Metabolic depression and sodium-potassium ATPase in the aestivating frog, Neobatrachus kunapalari

Abstract

In aestivation the metabolic rate of the Australian desert frog Neobatrachus kunapalari was 50–67% lower than in the non-aestivating state. The rate of O₂ consumption of isolated muscle, skin and brain was measured in both metabolic states. The average rate of O₂ consumption of muscle was 30% lower and brain 50% lower in aestivating frogs, while the rate of O₂ consumption of skin was the same. The reduction in muscle could account for a large proportion of whole animal metabolic depression. To look for evidence of a reduction in energy demand in the tissues we measured the ouabain-sensitive fraction of tissue rate of O₂ consumption, which is considered to be the proportion of metabolism used for transmembrane Na⁺/K⁺ pumping. Ouabain inhibited the in vitro rate of O₂ consumption of skin by a average of 20% and of brain by an average of 30%. However, in muscle, ouabain stimulated in vitro O₂ consumption. Despite the 50% reduction in the in vitro rate of O₂ consumption of brain during aestivation, neither the ouabain-sensitive nor ouabain-insensitive fractions were found be statistically different, possibly because of the large individual variation in the degree of ouabain inhibition. A reduction in the level of ion pumping during aestivation was therefore not demonstrated in any tissue. Measurement of the level of the enzyme Na⁺K⁺-ATPase in skeletal muscle, ventricle, kidney and brain showed that there was no change in the amount of this enzyme in the aestivating frogs. Measurement of the levels of adenylates in muscle and liver showed that the adenylate energy charge was maintained in aestivation, but that there was a reduction in ATP in liver and a reduction in the level of total adenylates in both tissues, which could be an adaptation of the tissues to a lower energy turnover.