Great adaptability of brown adipose tissue mitochondria to extreme ambient temperatures in control and cold-acclimated gerbils as compared with mice.

1. The gerbil (Gerbillus campestris) is a desert rodent able to tolerate high (38 degrees C) and low (-20 degrees C) ambient temperatures, probably due to both its low resting metabolic rate in hot environment and its high peak metabolic rate in cold. 2. Measurement of mitochondrial state IV respiration and cytochrome-oxidase activity (COX) were made in interscapular brown adipose tissue (IBAT), liver and hind limb muscles of gerbils and mice of nearly equal body mass, acclimated for 4 weeks at cold ambient temperature (CA) or reared at thermoneutrality (TN). 3. The most striking difference between these two animal species appears to be in IBAT mitochondria: in TN animals, the level of state IV respiration and COX activity was lower in gerbils than in mice, but the cold acclimation-induced increase in these parameters was greater in gerbils than in mice. 4. Alternatively, in gerbils as in mice, cold acclimation induced a reduction in muscle mitochondrial COX activity. No important change due to cold acclimation was observed in liver mitochondria, either in gerbils or in mice. 5. As compared with mice, the lower state IV respiration in IBAT mitochondria from TN gerbils may explain their low RMR, whereas the higher COX activity of IBAT mitochondria from CA gerbils may explain their higher PMR. 6. As a result of this great adaptability of BAT mitochondria, the gerbil seemed to be able to live in a wide range of ambient temperatures in its natural habitat.