Skeletal muscle fuel selection occurs at the mitochondrial level

Area of Science:

• * Comparative physiology
• * Mitochondrial biochemistry
• * Exercise metabolism

Background:

• * Mammals and birds exhibit distinct substrate utilization patterns during exercise.
• * Muscle fuel selection is influenced by factors from storage to mitochondrial level.
• * Mitochondria play a critical role in determining fuel preference.

Purpose of the Study:

• * To investigate fuel preferences of isolated mammalian and avian locomotory muscle mitochondria.
• * To compare substrate kinetics and fuel competition in mitochondria from both species.

Main Methods:

• * Assessed mitochondrial respiration kinetics (Km,ADP and Vmax) with various substrates.
• * Determined fuel competition using mass balance, oxygen consumption, and metabolite data.
• * Measured electron transport chain electron conductance in sonicated mitochondria.

Main Results:

• * Avian mitochondria showed higher Km,ADP and strongly favored fatty acids over pyruvate.
• * Mammalian mitochondria preferred fatty acids at lower flux but favored pyruvate/glutamate when available.
• * Avian mitochondria exhibited twofold higher electron transport chain conductance.

Conclusions:

• * Significant fuel selection occurs within the mitochondrial matrix.
• * Avian flight muscle mitochondria are biased towards fatty acid oxidation, potentially via enhanced beta-oxidation.
• * Differences in mitochondrial substrate selection contribute to distinct exercise physiology in mammals and birds.