Energetics for activity in the salamanderAmphiuma tridactylum

Summary

Various metabolic parameters were measured in relation to activity in the salamanderAmphiuma tridactylum. Cutaneous O₂ consumption rate ($\dot V_{O_2 }$) did not change with activity (Fig. 1B). Pulmonary$\dot V_{O_2 }$ did not increase during activity, but did increase after activity, repaying the O₂ debt (Fig. 1). Changes in lactate, glycogen and glucose indicated that: 1) the energy for activity is primarily derived from oxidation of muscle glycogen to lactate; 2) gluconeogenesis reaches a peak at 5 h after activity; and 3) total replenishment of muscle lactate may not occur until after the animal feeds again (Figs. 2,3). The measured O₂ debt of activity was 266.47 μl g⁻¹ (Fig. 1B). The amount of excess lactate generated (1.52 mg g⁻¹), estimates of O₂ stores, and estimates of high energy phosphate stores were used to calculate an O₂ debt (265.61 μl g⁻¹) which agreed with the measured O₂ debt (Fig. 4); 76% is a lactacid and 24% is an alactacid debt. The total energy cost of activity was calculated from similar estimates (Fig. 5). It is suggested thatAmphiuma can remain active longer than other amphibians which have similar anaerobic capacities because of the efficiency of swimming as a means of locomotion. The results are used in interpreting evolution of the lungs ofAmphiuma.