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.
Mourtzakis
M
M
Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada. mmourtza@healthy.uwaterloo.ca
Graham
T E
TE
González-Alonso
J
J
Saltin
B
B
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