Glutamate availability is important in intramuscular amino acid metabolism and TCA cycle intermediates but does not affect peak oxidative metabolism.
Muscle glutamate is central to reactions producing 2-oxoglutarate, a tricarboxylic acid (TCA) cycle intermediate that essentially expands the TCA cycle intermediate pool during exercise. Paradoxically, muscle glutamate drops approximately 40-80% with the onset of exercise and 2-oxoglutarate declines in early exercise. To investigate the physiological relationship between glutamate, oxidative metabolism, and TCA cycle intermediates (i.e., fumarate, malate, 2-oxoglutarate), healthy subjects trained (T) the quadriceps of one thigh on the single-legged knee extensor ergometer (1 h/day at 70% maximum workload for 5 days/wk), while their contralateral quadriceps remained untrained (UT). After 5 wk of training, peak oxygen consumption (VO2peak) in the T thigh was greater than that in the UT thigh (P<0.05); VO2peak was not different between the T and UT thighs with glutamate infusion. Peak exercise under control conditions revealed a greater glutamate uptake in the T thigh compared with rest (7.3+/-3.7 vs. 1.0+/-0.1 micromol.min(-1).kg wet wt(-1), P<0.05) without increase in TCA cycle intermediates. In the UT thigh, peak exercise (vs. rest) induced an increase in fumarate (0.33+/-0.07 vs. 0.02+/-0.01 mmol/kg dry wt (dw), P<0.05) and malate (2.2+/-0.4 vs. 0.5+/-0.03 mmol/kg dw, P<0.05) and a decrease in 2-oxoglutarate (12.2+/-1.6 vs. 32.4+/-6.8 micromol/kg dw, P<0.05). Overall, glutamate infusion increased arterial glutamate (P<0.05) and maintained this increase. Glutamate infusion coincided with elevated fumarate and malate (P<0.05) and decreased 2-oxoglutarate (P<0.05) at peak exercise relative to rest in the T thigh; there were no further changes in the UT thigh. Although glutamate may have a role in the expansion of the TCA cycle, glutamate and TCA cycle intermediates do not directly affect VO2peak in either trained or untrained muscle.
Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada. mmourtza@healthy.uwaterloo.ca
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M
Mourtzakis
T E
TE
Graham
J
J
González-Alonso
B
B
Saltin
D000328:Adult; D000410:Alanine Transaminase / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism*; D015308:Anaerobic Threshold / Q000502:physiology; D001786:Blood Glucose / Q000378:metabolism; D002245:Carbon Dioxide / Q000097:blood; D002952:Citric Acid Cycle / Q000502:physiology*; D005934:Glucagon / Q000097:blood; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000097:blood; D007866:Leg / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D009929:Organ Size / Q000502:physiology; D010084:Oxidation-Reduction; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology
D000596:Amino Acids; D001786:Blood Glucose; D007328:Insulin; D002245:Carbon Dioxide; D018698:Glutamic Acid; D005934:Glucagon; D000410:Alanine Transaminase; D009584:Nitrogen; D010100:Oxygen