Fig. 3. (A) Measurements of whole-animal oxygen consumption of Rana temporaria under control conditions (in water but with access to the surface for air-breathing) and after 90 days of cold-submergence in normoxic (P_O2=21 kPa) or hypoxic (P_O2=8 kPa) water at 3 °C. (B) Respiration rates of skeletal muscle mitochondria isolated from frogs during normoxic and hypoxic hibernation, in state 4 and at 125 mV. Frog mitochondrial proton leak rate was measured at 25 °C because the respiration rate of frog mitochondria was so low at 3 °C that it was impossible to carry out accurate measurements with the apparatus used (St-Pierre et al., 2000a). Since that time, Q₁₀ values between 3 and 20 °C have been determined for the state 4 respiration rate of mitochondria (St-Pierre et al., 2000c). As the Q₁₀ values do not differ between control and 4-month-hypoxic-submerged frogs (St-Pierre et al., 2000c), the proton leak rate comparisons at 25 °C between the two groups of frogs should be adequate. Values are means ± S.E.M.; N=5 for control frogs, N=4 for 4-month-submerged frogs. From Boutilier (2001) with permission.