METABOLIC DEPRESSION AND SODIUM-POTASSIUM ATPASE IN THE ESTIVATING FROG, NEOBATRACHUS-KUNAPALARI

In aestivation the metabolic rate of the Australian desert frog Neobat rachus kunapalari was 50-67% lower than in the non-aestivating state. The rate of O-2 consumption of isolated muscle, skin and brain was mea sured in both metabolic states. The average rate of O-2 consumption of muscle was 30% lower and brain 50% lower in aestivating frogs, while the rate of O-2 consumption of skin was the same. The reduction in mus cle could account for a large proportion of whole animal metabolic dep ression. To look for evidence of a reduction in energy demand in the t issues we measured the ouabain-sensitive fraction of tissue rate of O- 2 consumption, which is considered to be the proportion of metabolism used for transmembrane Na+/K+ pumping. Ouabain inhibited the in vitro rate of O-2 consumption of skin by a average of 20% and of brain by an average of 30%. However, in muscle, ouabain stimulated in vitro O-2 c onsumption. Despite the 50% reduction in the in vitro rate of O-2 cons umption 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 ou abain inhibition. A reduction in the level of ion pumping during aesti vation was therefore not demonstrated in any tissue. Measurement of th e level of the enzyme Na+K+-ATPase in skeletal muscle, ventricle, kidn ey and brain showed that there was no change in the amount of this enz yme in the aestivating frogs. Measurement of the levels of adenylates in muscle and liver showed that the adenylate energy charge was mainta ined in aestivation, but that there was a reduction in ATP in liver an d a reduction in the level of total adenylates in both tissues, which could be an adaptation of the tissues to a lower energy turnover.