Thermal sensitivity of cardiac mitochondrial metabolism in an ectothermic species from a cold environment, Atlantic wolffish (Anarhichas lupus)

To produce energy, mitochondria use oxidative phosphorylation, a multistep process involving several integrated reactions influenced by temperature. In order to identify which step in the process was most sensitive to temperature in a cold-temperate ectothermic species, we measured the thermal sensitivity of mitochondrial oxidative phosphorylation, as well as the thermal sensitivity of each individual step in this process, in mitochondria isolated from the heart of Atlantic wolffish (Anarhichas lupus). The thermal sensitivity of oxidative phosphorylation (coupled, ADP-stimulated), measured in the presence of pyruvate and malate as substrates, and those of Complexes II and IV activities were the same over the whole range of assay temperatures (5 to 35 °C). In contrast, the thermal sensitivity of Complexes I and III, ATPase, pyruvate dehydrogenase and citrate synthase could not be correlated with the thermal sensitivity of oxidative phosphorylation. The first step in the process of oxidative phosphorylation to be negatively affected by increased temperature was shown to be Complex III, followed by the Complex I. This occurred at temperatures above the tolerance limit and well above the range of temperatures occupied by the species. Our results identify specific steps within the electron transport system as potential control point limiting the capacity of Atlantic wolffish cardiac mitochondrial metabolism in response to changes in temperature.