HUMAN SKELETAL MUSCLE MALONYL-CoA AT REST AND DURING PROLONGED SUBMAXIMAL EXERCISE 445

Previous literature has indicated that malonyl-CoA content in rat skeletal muscle decreases with prolonged submaximal exercise. It has been suggested that this contraction-induced decrease in malonyl-CoA is instrumental in the increase of fatty acid oxidation during exercise. The purpose of this study was to measure malonyl-CoA content in human vastus lateralis muscle at rest and during submaximal exercise. Eight males and 1 female cycled for 70 min (10 min at 40% and 60 min at 65% VO2 max). Needle biopsies were obtained at rest, 10 min, 20 min, and 70 min of exercise. Malonyl-CoA content in pre-exercise biopsy samples determined by HPLC was 1.53 ± 0.18μmol·kg-1 dry weight. Malonyl-CoA content did not change significantly during exercise (1.39 ± 0.21 at 10 min, 1.46 ± 0.14 at 20 min and 1.22 ± 0.15 μmol·kg-1 dry wt at 70 min). This was in spite of a significant decrease in RER from 0.95 ± 0.02 to 0.89 ± 0.02 during 60 min at 65% VO2 max. In contrast, malonyl-CoA content determined by HPLC in perfused rat red gastrocnemius muscle decreased significantly during 20 min of stimulation at 0.7 Hz (3.44± 0.54 and 1.64 ± 0.23 nmol·g-1 dry wt, pre and post stimulation, respectively, n=9). We conclude that human skeletal muscle malonyl-CoA content 1) is less than reported in rat skeletal muscle at rest, 2) does not decrease with prolonged submaximal exercise, and 3) is not predictive of increased fatty acid oxidation during exercise.