Early alterations in soleus GLUT-4, glucose transport, and glycogen in voluntary running rats.
Voluntary wheel running (WR) by juvenile female rats was used as a noninterventional model of soleus muscle functional overload to study the regulation of insulin-stimulated glucose transport activity by the glucose transporter (GLUT-4 isoform) protein level and glycogen concentration. Soleus total protein content was significantly greater (+18%; P < 0.05) than in age-matched controls after 1 wk of WR, and this hypertrophic response continued in weeks 2-4 (+24-32%). GLUT-4 protein was 39% greater than in controls in 1-wk WR soleus, and this adaptation was accompanied by a similar increase in in vitro insulin-stimulated glucose transport activity (+29%). After 2 and 4 wk of WR, however, insulin-stimulated glucose transport activity had returned to control levels, despite a continued elevation (+25-28%) of GLUT-4 protein. At these two time points, glycogen concentration was significantly enhanced in WR soleus (+21-42%), which coincided with significant reductions in glycogen synthase activity ratios (-23 to -41%). These results indicate that, in this model of soleus muscle functional overload, the GLUT-4 protein level may initially regulate insulin-stimulated glucose transport activity in the absence of changes in other modifying factors. However, this regulation of glucose transport activity by GLUT-4 protein may be subsequently overridden by elevated glycogen concentration.
Henriksen
E J
EJ
Department of Exercise and Sport Sciences, University of Arizona, Tucson 85721.
Halseth
A E
AE
D000818:Animals; D001835:Body Weight / Q000502:physiology; D005260:Female; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D006003:Glycogen / Q000378:metabolism*; D006593:Hexokinase / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism; D009132:Muscles / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D009929:Organ Size / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495694:Slc2a4 protein, rat; D006003:Glycogen; D006593:Hexokinase; D005947:Glucose