title: Effect of carbohydrate supplementation on postexercise GLUT-4 protein expression in skeletal muscle.
abstract: The effect of carbohydrate supplementation on skeletal muscle glucose transporter GLUT-4 protein expression was studied in fast-twitch red and white gastrocnemius muscle of Sprague-Dawley rats before and after glycogen depletion by swimming. Exercise significantly reduced fast-twitch red muscle glycogen by 50%. During a 16-h exercise recovery period, muscle glycogen returned to control levels (25.0 +/- 1.4 micromol/g) in exercise-fasted rats (24.2 +/- 0. 3 micro). However, when carbohydrate supplementation was provided during and immediately postexercise by intubation, muscle glycogen increased 77% above control (44.4 +/- 2.1 micromol/g). Exercise-fasting resulted in an 80% increase in fast-twitch red muscle GLUT-4 mRNA but only a 43% increase in GLUT-4 protein concentration. Conversely, exercise plus carbohydrate supplementation elevated fast-twitch red muscle GLUT-4 protein concentration by 88% above control, whereas GLUT-4 mRNA was increased by only 40%. Neither a 16-h fast nor carbohydrate supplementation had an effect on fast-twitch red muscle GLUT-4 protein concentration or on GLUT-4 mRNA in sedentary rats, although carbohydrate supplementation increased muscle glycogen concentration by 40% (35.0 +/- 0.9 micromol/g). GLUT-4 protein in fast-twitch white muscle followed a pattern similar to fast-twitch red muscle. These results indicate that carbohydrate supplementation, provided with exercise, will enhance GLUT-4 protein expression by increasing translational efficiency. Conversely, postexercise fasting appears to upregulate GLUT-4 mRNA, possibly to amplify GLUT-4 protein expression on an increase in glucose availability. These regulatory mechanisms may help control muscle glucose uptake in accordance with glucose availability and protect against postexercise hypoglycemia.
authors.affiliation: Exercise Physiology and Metabolism Laboratory, Department of Kinesiology and Health Education, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: C H
authors.initials: CH
authors.lastname: Kuo
authors.forename: D G
authors.initials: DG
authors.lastname: Hunt
authors.forename: Z
authors.initials: Z
authors.lastname: Ding
authors.forename: J L
authors.initials: JL
authors.lastname: Ivy
mesh_terms: D000818:Animals; D004040:Dietary Carbohydrates / Q000494:pharmacology*; D019587:Dietary Supplements; D005215:Fasting / Q000502:physiology; D051275:Glucose Transporter Type 4; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009043:Motor Activity / Q000502:physiology*; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D014176:Protein Biosynthesis / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013550:Swimming
chemical_list: D004040:Dietary Carbohydrates; D051275:Glucose Transporter Type 4; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D012333:RNA, Messenger; C495694:Slc2a4 protein, rat