Effects of Temperature and Hypoxia‐Reoxygenation on Mitochondrial Oxidative Capacity and Volume, Oncorhynchus mykiss

Abstract

We investigated the effects of temperature and hypoxia‐reoxygenation (H‐RO) on mitochondrial bioenergetics and volume regulation. Oxygen consumption rates in isolated rainbow trout liver mitochondria were measured at 5, 13 and 25 oC before and after exposure to varying durations (5, 15 and 30 min) of hypoxia and reoxygenation. Subsequently, exposure to 15 min of H‐RO at 13 oC was used to probe the involvement of mitochondrial potassium channels (mitoKATP) in H‐RO‐induced mitochondrial volume changes. Our results showed that the stimulatory effect of temperature on state 3 respiration was reduced by H‐RO. In contrast, H‐RO acted cooperatively with temperature to stimulate state 4 respiration. Interestingly, while H‐RO reduced the thermal sensitivity of state 3 at the low (5‐13 oC) temperature range, it increased that of state 4 at both the low and high (13‐25 oC) ranges. These disparate effects of H‐RO on both the rates of state 3 and 4 respiration and their thermal sensitivities markedly reduced the mitochondrial coupling efficiency. We also found that diazoxide, a mitoKATP opener, protected mitochondria against H‐RO‐induced mitochondrial swelling. Overall, our findings indicate that the effects of H‐RO on mitochondrial oxidative capacity are exacerbated by temperature and that mitoKATP mediate H‐RO‐induced mitochondrial volume changes.