AEROBIC AND ANAEROBIC CONTRIBUTIONS TO SUSTAINED ACTIVITY IN XENOPUS-LAEVIS

In conditions of declining water PO, Xenopus obtains the majority of resting oxygen needs from lung breathing at 15° and 25°C. The critical oxygen tension was 120 ± 9 m Hg at 15°C, and 90 ± 10 m Hg at 25°C. During 30 min stimulation of activity to complete exhaustion at 15°C, frogs exhibited an aerobic capacity of 1.7 μl O2·g-1·h-1 and accumulated 2.22 mg lactate · g-1. Following activity these animals exhibited an oxygen of debt 49.2 μl O2·g-1. At 25°C, Xe nopus had an aerobic capacity of 16.1 μl O2·g-1 and accumulated 1.94 mg lactate · g-1. Following activity, 25°C frogs exhibited an oxygen debt of 261.9 μl O2·g-1. Thus at 15°C, Xenopus acquires 85% of the ATP used during a bout of sustained exhaustive activity from anaerobic sources, and 98% at 25°C. Recovery from exhaustive activity was complete after 5 h at 25°C and 9 h at 15°C. Comparison of these data with those of other amphibians stimulated to sustained activity suggests that aquatic amphibians can tolerate a larger lactate load than can terrestrial forms. © 1978.