title: Effect of insulin-like factors on glucose transport activity in unweighted rat skeletal muscle.
abstract: We have previously demonstrated that mechanical unweighting of the soleus muscle by hindlimb suspension leads to increases in insulin receptor binding, muscle/fat-specific glucose transporter (GLUT-4) protein levels, and insulin-stimulated glucose transport activity. The present study used a novel approach to further evaluate the potential role of postreceptor binding mechanisms in this enhanced insulin effect after unweighting. Insulin-like growth factor I (IGF-I), vanadate, and phospholipase C were used to stimulate glucose transport activity independently of insulin receptor binding. Soleus glucose transport activity (assessed by 2-deoxyglucose uptake) was evaluated in vitro with soleus strips (approximately 18 mg). Progressively increased responses to maximally effective doses of insulin or IGF-I were observed after 3 and 6 days of unweighting compared with weight-matched control strips. Enhanced maximal responses to vanadate (6 days only) and phospholipase C (3 and 6 days) for 2-deoxyglucose uptake were also observed. The results of this study 1) provide evidence that post-insulin receptor binding mechanisms also play a role in the enhanced response of the insulin-dependent pathway for stimulation of glucose transport in unweighted skeletal muscle and 2) indicate that IGF-I action on glucose transport is included in this enhanced response in unweighted muscle.
authors.affiliation: Department of Exercise and Sport Sciences, University of Arizona, Tucson 85721.
authors.forename: E J
authors.initials: EJ
authors.lastname: Henriksen
authors.forename: L S
authors.initials: LS
authors.lastname: Ritter
mesh_terms: D000818:Animals; D001835:Body Weight / Q000187:drug effects; D003847:Deoxyglucose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D009929:Organ Size / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D011972:Receptor, Insulin / Q000187:drug effects / Q000378:metabolism; D010738:Type C Phospholipases / Q000494:pharmacology; D014638:Vanadates / Q000494:pharmacology; D014893:Weightlessness / Q000009:adverse effects*
chemical_list: D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495694:Slc2a4 protein, rat; D014638:Vanadates; D007334:Insulin-Like Growth Factor I; D003847:Deoxyglucose; D011972:Receptor, Insulin; D010738:Type C Phospholipases; D005947:Glucose