Metabolic depression and Na+/K+ gradients in the aestivating Australian goldfields frog, Neobatrachus wilsmorei

Abstract

During aestivation the metabolic rate of the Australian goldfields frog Neobatrachus wilsmorei was reduced by 80% from its standard metabolic rate. The in vitro rate of oxygen consumption of isolated muscle and skin from aestivating frogs was up to 50% lower than that of the non-aestivating frogs. This in vitro rate of oxygen consumption was maintained for 6–12 h, indicating an intrinsic metabolic depression of tissues during aestivation. Frogs became dehydrated during aestivation. Muscle, skin and liver also became dehydrated during aestivation, but brain and kidney did not. Na⁺ and K⁺ contents and extracellular space measurement for muscle indicated that ion gradients were maintained across the muscle cell membrane during aestivation. Increases in plasma concentrations of Na⁺ and K⁺ were matched with similar increases in muscle intracellular ion concentrations. Extracellular space measurements were unsuccessful in the other tissues, but K⁺ content in all tissues (per dry weight) was maintained during aestivation, and the concentration of plasma K⁺ did not increase above that which can be accounted for by dehydration, indicating that K⁺ gradients were maintained.