Skeletal muscle malonyl-CoA content at the onset of exercise at varying power outputs in humans

• Published in: American journal of physiology: endocrinology and metabolism 1998-06, Vol.274 (6), p.E1080-E1085
• Main Authors: Odland, L. Maureen, Howlett, Richard A, Heigenhauser, George J. F, Hultman, Eric, Spriet, Lawrence L
• Format: Article
• Language: English
• ISSN: 0193-1849; 1522-1555
• DOI: 10.1152/ajpendo.1998.274.6.E1080

Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario N1G 2W1; Department of Medicine, McMaster University, Hamilton, Ontario, Canada L8N 3Z5; and Department of Clinical Chemistry, Huddinge University Hospital, S 141 86 Huddinge, Sweden 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 O 2 consumption ( O 2 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% O 2 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 µmol/kg dry muscle). During exercise at 35% O 2 max , M-CoA decreased from rest at 1 min (1.85 ± 0.29 to 1.20 ± 0.12 µmol/kg dry muscle) but returned to rest level by 10 min (1.86 ± 0.25 µmol/kg dry muscle). M-CoA content did not decrease during cycling at 65% O 2 max . At 90% O 2 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% O 2 max . Furthermore, M-CoA content does not increase during exercise at 90% O 2 max and does not contribute to the lower rate of fat oxidation at this power output. fatty acid oxidation; acetyl-coenzyme A; acetyl-coenzyme A carboxylase; carnitine palmitoyltransferase I; high-performance liquid chromatography; malonyl-coenzyme A