title: Short-term exercise training in humans reduces AMPK signalling during prolonged exercise independent of muscle glycogen.
abstract: We examined the effect of short-term exercise training on skeletal muscle AMP-activated protein kinase (AMPK) signalling and muscle metabolism during prolonged exercise in humans. Eight sedentary males completed 120 min of cycling at 66 +/- 1% , then exercise trained for 10 days, before repeating the exercise bout at the same absolute workload. Participants rested for 72 h before each trial while ingesting a high carbohydrate diet (HCHO). Exercise training significantly (P < 0.05) attenuated exercise-induced increases in skeletal muscle free AMP: ATP ratio and glucose disposal and increased fat oxidation. Exercise training abolished the 9-fold increase in AMPK alpha2 activity observed during pretraining exercise. Since training increased muscle glycogen content by 93 +/- 12% (P < 0.01), we conducted a second experiment in seven sedentary male participants where muscle glycogen content was essentially matched pre- and post-training by exercise and a low CHO diet (LCHO; post-training muscle glycogen 52 +/- 7% less than in HCHO, P < 0.001). Despite the difference in muscle glycogen levels in the two studies we obtained very similar results. In both studies the increase in ACCbeta Ser(221) phosphorylation was reduced during exercise after training. In conclusion, there is little activation of AMPK signalling during prolonged exercise following short-term exercise training suggesting that other factors are important in the regulation of glucose disposal and fat oxidation under these circumstances. It appears that muscle glycogen is not an important regulator of AMPK activation during exercise in humans when exercise is begun with normal or high muscle glycogen levels.
authors.affiliation: Department of Physiology, University of Melbourne, Parkville, Victoria, Australia. mcconell@unimelb.edu.au
authors.forename: Glenn K
authors.initials: GK
authors.lastname: McConell
authors.forename: Robert S
authors.initials: RS
authors.lastname: Lee-Young
authors.forename: Zhi-Ping
authors.initials: ZP
authors.lastname: Chen
authors.forename: Nigel K
authors.initials: NK
authors.lastname: Stepto
authors.forename: Ngan N
authors.initials: NN
authors.lastname: Huynh
authors.forename: Terry J
authors.initials: TJ
authors.lastname: Stephens
authors.forename: Benedict J
authors.initials: BJ
authors.lastname: Canny
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Kemp
mesh_terms: D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase / Q000378:metabolism; D001786:Blood Glucose; D004040:Dietary Carbohydrates / Q000008:administration & dosage; D015444:Exercise / Q000502:physiology*; D005947:Glucose / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D050356:Lipid Metabolism; D008297:Male; D009097:Multienzyme Complexes / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D009097:Multienzyme Complexes; D012694:Serine; D006003:Glycogen; C526181:PRKAA2 protein, human; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase; D005947:Glucose