title: Metabolic, enzymatic, and transporter responses in human muscle during three consecutive days of exercise and recovery.
abstract: This study investigated the responses in substrate- and energy-based properties to repetitive days of prolonged submaximal exercise and recovery. Twelve untrained volunteers (Vo(2)(peak) = 44.8 +/- 2.0 ml.kg(-1).min(-1), mean +/- SE) cycled ( approximately 60 Vo(2)(peak)) on three consecutive days followed by 3 days of recovery. Tissue samples were extracted from the vastus lateralis both pre- and postexercise on day 1 (E1), day 3 (E3), and during recovery (R1, R2, R3) and were analyzed for changes in metabolism, substrate, and enzymatic and transporter responses. For the metabolic properties (mmol/kg(-1) dry wt), exercise on E1 resulted in reductions (P < 0.05) in phosphocreatine (PCr; 80 +/- 1.9 vs. 41.2 +/- 3.0) and increases (P < 0.05) in inosine monophosphate (IMP; 0.13 +/- 0.01 vs. 0.61 +/- 0.2) and lactate (3.1 +/- 0.4 vs. 19.2 +/- 4.3). At E3, both IMP and lactate were lower (P < 0.05) during exercise. For the transporters, the experimental protocol resulted in a decrease (P < 0.05) in glucose transporter-1 (GLUT1; 29% by R1), an increase in GLUT4 (29% by E3), and increases (P < 0.05) for both monocarboxylate transporters (MCT) (for MCT1, 23% by R2 and for MCT4, 18% by R1). Of the mitochondrial and cytosolic enzyme activities examined, cytochrome c oxidase (COX), and hexokinase were both reduced (P < 0.05) by exercise at E1 and in the case of hexokinase and phosphorylase by exercise on E3. With the exception at COX, which was lower (P < 0.05) at R1, no differences in enzyme activities existed at rest between E, E3, and recovery days. Results suggest that the glucose and lactate transporters are among the earliest adaptive responses of substrate and metabolic properties studied to the sudden onset of regular low-intensity exercise.
authors.affiliation: Dept. of Kinesiology, Univ. of Waterloo, Waterloo, ON, Canada N2L 3G1. green@healthy.uwaterloo.ca
authors.forename: Howard J
authors.initials: HJ
authors.lastname: Green
authors.forename: Eric
authors.initials: E
authors.lastname: Bombardier
authors.forename: Todd A
authors.initials: TA
authors.lastname: Duhamel
authors.forename: Riley D
authors.initials: RD
authors.lastname: Stewart
authors.forename: A Ross
authors.initials: AR
authors.lastname: Tupling
authors.forename: Jing
authors.initials: J
authors.lastname: Ouyang
mesh_terms: D000220:Adaptation, Biological / Q000502:physiology; D000227:Adenine Nucleotides / Q000378:metabolism; D000293:Adolescent; D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D003401:Creatine / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005947:Glucose / Q000378:metabolism; D051246:Glucose Transport Proteins, Facilitative / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006593:Hexokinase / Q000378:metabolism; D006801:Humans; D007291:Inosine Monophosphate / Q000378:metabolism; D019344:Lactic Acid / Q000097:blood / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism*; D027501:Monocarboxylic Acid Transporters / Q000378:metabolism; D018482:Muscle, Skeletal / Q000201:enzymology* / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism; D006005:Phosphorylases / Q000378:metabolism; D052097:Quadriceps Muscle / Q000378:metabolism
chemical_list: D000227:Adenine Nucleotides; D001786:Blood Glucose; D051246:Glucose Transport Proteins, Facilitative; D018840:HSP70 Heat-Shock Proteins; D026901:Membrane Transport Proteins; D027501:Monocarboxylic Acid Transporters; D010710:Phosphates; D010725:Phosphocreatine; D007291:Inosine Monophosphate; D019344:Lactic Acid; D019298:Glucose-6-Phosphate; D006003:Glycogen; D003576:Electron Transport Complex IV; D006005:Phosphorylases; D006593:Hexokinase; D005947:Glucose; D003401:Creatine