Skeletal muscle malonyl-CoA content at the onset of exercise at varying power outputs in humans.
To investigate the regulation of intramuscular fuel selection, we measured the malonyl-CoA (M-CoA) content in human skeletal muscle at three exercise power outputs [35, 65, and 90% maximal rate of O2 consumption (VO2 max)]. Four males and four females cycled for 10 min at one power output on three separate occasions with muscle biopsies sampled at rest and at 1 and 10 min. The respiratory exchange ratio was 0.84 +/- 0.03, 0.92 +/- 0.02, and >1.0 at 35, 65 and 90% VO2 max, respectively. Muscle lactate content increased and phosphocreatine content decreased as a function of power output. Pyruvate dehydrogenase a activity increased from 0.40-0.64 mmol . kg wet muscle-1 . min-1 at rest to 1.57 +/- 0.28, 2.80 +/- 0.41, and 3. 28 +/- 0.27 mmol . kg wet muscle-1 . min-1 after 1 min of cycling at the three power outputs, respectively. Mean resting M-CoA contents were similar at all power outputs (1.85-1.98 micromol/kg dry muscle). During exercise at 35% VO2 max, M-CoA decreased from rest at 1 min (1.85 +/- 0.29 to 1.20 +/- 0.12 micromol/kg dry muscle) but returned to rest level by 10 min (1.86 +/- 0.25 micromol/kg dry muscle). M-CoA content did not decrease during cycling at 65% VO2 max. At 90% VO2 max, M-CoA did not increase despite significant acetyl-CoA accumulation (the substrate for M-CoA synthesis). The data suggest that a decrease in M-CoA content is not required for the increase in free fatty acid uptake and oxidation that occurs during exercise at 35 and 65% VO2 max. Furthermore, M-CoA content does not increase during exercise at 90% VO2 max and does not contribute to the lower rate of fat oxidation at this power output.
Odland
L M
LM
Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
Howlett
R A
RA
Heigenhauser
G J
GJ
Hultman
E
E
Spriet
L L
LL
D000255:Adenosine Triphosphate / Q000378:metabolism; D000328:Adult; D015444:Exercise / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000378:metabolism; D006801:Humans; D019344:Lactic Acid / Q000378:metabolism; D008297:Male; D008316:Malonyl Coenzyme A / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D010725:Phosphocreatine / Q000378:metabolism; D011659:Pulmonary Gas Exchange; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism
D005230:Fatty Acids, Nonesterified; D011768:Pyruvate Dehydrogenase Complex; D010725:Phosphocreatine; D019344:Lactic Acid; D008316:Malonyl Coenzyme A; D000255:Adenosine Triphosphate; D005947:Glucose