Oxygen consumption by mitochondria from an endotherm and an ectotherm

Comparisons of metabolic properties of mitochondria from an endothermic and an ectothermic vertebrate were performed. Oxygen (O-2) consumption rates of liver mitochondria from laboratory mice and western fence lizard (Sceloporus occidentalis) were determined over a range of temperatures (10, 20, 30 and 37 degrees C) and in the presence of a variety of substrates. At 37 degrees C the O-2 consumption rate of mouse mitochondria was 4-11 times higher than lizard mitochondria in the presence of five of eight substrates. This range of differences is similar to differences reported for O-2 consumption of endothermic animals, tissues and cells over those of ectotherms. Thermal sensitivity of mitochondria was measured by calculation of Q(10)s for O-2 consumption. Q(10)s were highest for mouse mitochondria overall. The range that showed the highest Q(10)s for the mouse mitochondria was 30-20 degrees C, whereas for the lizard mitochondria it was 20-10 degrees C. Thus, mitochondria from the ectotherm showed a lower degree of temperature sensitivity than did mitochondria from the endotherm. The preferred substrate for all mitochondria at all temperatures was succinate, but mouse mitochondria then showed some preference for alpha-ketoglutarate and citrate, whereas lizard mitochondria showed a preference for pyruvate and malate + pyruvate. (C) 1999 Elsevier Science Inc. All rights reserved.