High temperature impairs mitochondrial function in rainbow trout cardiac mitochondria.

Area of Science:

• Mitochondrial physiology
• Cardiovascular research
• Environmental adaptation

Background:

• Mitochondria are vital for cellular energy production via oxidative phosphorylation.
• Temperature significantly impacts animal aerobic scope and thermal tolerance by affecting mitochondrial function.
• Rainbow trout (Oncorhynchus mykiss) are ectotherms sensitive to environmental temperature changes.

Purpose of the Study:

• To investigate the effects of temperature (5-30°C) on isolated cardiac mitochondrial respiration in rainbow trout.
• To identify temperature-induced limitations on mitochondrial function and their relationship to aerobic scope.
• To elucidate the specific roles of phosphorylation and mitochondrial respiratory complexes in thermal tolerance.

Main Methods:

• High-resolution respirometry was used to measure mitochondrial respiration rates.
• Spectrophotometric enzyme activity assays assessed the function of specific mitochondrial complexes.
• Arrhenius breakpoint temperature analysis identified critical temperature thresholds for mitochondrial function.

Main Results:

• Mitochondrial respiration under phosphorylating and uncoupled conditions increased up to 20°C, then plateaued.
• Non-phosphorylating proton leak respiration continued to increase up to 30°C.
• Complex I (NADH dehydrogenase) activity decreased above 20°C, while Complex II (succinate dehydrogenase) activity remained stable.
• Impaired phosphorylation and decreased Complex I activity were observed at higher temperatures.

Conclusions:

• Temperature-induced declines in cardiac mitochondrial function in rainbow trout are linked to impaired phosphorylation and Complex I activity.
• These mitochondrial limitations coincide with the optimal temperature range for trout aerobic scope.
• Understanding these mechanisms is crucial for predicting fish responses to warming aquatic environments.