Stability of GLUT-1 and GLUT-4 expression in perfused rat muscle stimulated by insulin and exercise.
In vivo exercise and insulin may change the concentrations of GLUT-4 protein and mRNA in muscle. We studied in vitro whether adaptations in glucose transporter expression are initiated during a single prolonged period of contractions or during insulin stimulation. Rat hindquarters were perfused at 7 mM glucose for 2 h with or without insulin (> 20,000 microU/ml) while the sciatic nerve of one leg was stimulated to produce repeated tetanic contractions. During electrical stimulation, contraction force decreased 93 +/- 1% (SE; n = 26) and muscle glycogen was markedly diminished (P < 0.05). Both contractions and insulin markedly increased glucose transport and uptake (P < 0.05). At the end of contractions, glycogen was higher in the presence of than in the absence of insulin (24 +/- 4 vs. 14 +/- 3 mumol/g for the soleus and 13 +/- 2 vs. 8 +/- 1 mumol/g for the red gastrocnemius, respectively; P < 0.05). In nonstimulated muscle, glucose transporter mRNA and protein concentrations were higher in the soleus than in the white gastrocnemius (GLUT-4 mRNA 184 +/- 18 vs. 131 +/- 36 arbitrary units; GLUT-1 mRNA 173 +/- 29 vs. 114 +/- 26 arbitrary units; GLUT-4 protein 0.96 +/- 0.09 vs. 0.46 +/- 0.03 arbitrary units; GLUT-1 protein 0.41 +/- 0.08 vs. 0.19 +/- 0.05 arbitrary units, respectively; P < 0.05). These concentrations were not changed by contractions or insulin. In conclusion, GLUT-1 and GLUT-4 mRNA and protein levels are higher in slow-twitch oxidative than in fast-twitch glycolytic fibers.(ABSTRACT TRUNCATED AT 250 WORDS)
Han
X X
XX
Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark.
Handberg
A
A
Petersen
L N
LN
Ploug
T
T
Galbo
H
H
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D006003:Glycogen / Q000378:metabolism; D006614:Hindlimb / Q000098:blood supply; D015151:Immunoblotting; D066298:In Vitro Techniques; D007328:Insulin / Q000097:blood / Q000494:pharmacology*; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000096:biosynthesis*; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000098:blood supply / Q000187:drug effects / Q000378:metabolism*; D005082:Physical Exertion / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology
D001786:Blood Glucose; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D012333:RNA, Messenger; C495679:Slc2a1 protein, rat; C495694:Slc2a4 protein, rat; D006003:Glycogen