Skeletal muscle fuel selection occurs at the mitochondrial level

Sarah Kuzmiak-Glancy, Wayne T. Willis

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


Mammals exponentially increase the rate of carbohydrate oxidation as exercise intensity rises, while birds combust lipid almost exclusively while flying at high percentages of aerobic capacity. The fuel oxidized by contracting muscle depends on many factors: whole-body fuel storage mass, mobilization, blood transport, cellular uptake, and substrate selection at the level of the mitochondrion. We examined the fuel preferences of mitochondria isolated from mammalian and avian locomotory muscles using two approaches. First, the influence of substrates on the kinetics of respiration (Km,ADP and Vmax) was evaluated. For all substrates and combinations, Km,ADP was generally twofold higher in avian mitochondria. Second, fuel competition between pyruvate, glutamate and/or palmitoyl-L-carnitine at three levels of ATP free energy was determined using the principle of mass balance and the measured rates of O2 consumption and metabolite accumulation/utilization. Avian mitochondria strongly spared pyruvate from oxidation when another substrate was available and fatty acid was the dominant substrate, regardless of energy state. Mammalian mitochondria exhibited some preference for fatty acid over pyruvate at lower flux (higher energy state), but exhibited a much greater tendency to select pyruvate and glutamate when available. Studies in sonicated mitochondria revealed twofold higher electron transport chain electron conductance in avian mitochondria. We conclude that substantial fuel selection occurs at the level of the mitochondrial matrix and that avian flight muscle mitochondria are particularly biased toward the selection of fatty acid, possibly by facilitating high β-oxidation flux by maintaining a more oxidized matrix.

Original languageEnglish (US)
Pages (from-to)1993-2003
Number of pages11
JournalJournal of Experimental Biology
Issue number11
StatePublished - Jun 1 2014
Externally publishedYes


  • Fuel selection
  • Mitochondrial function
  • Skeletal muscle mitochondria

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Physiology
  • Aquatic Science
  • Animal Science and Zoology
  • Molecular Biology
  • Insect Science


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