EFFECT OF SOLEUS UNWEIGHTING ON STIMULATION OF INSULIN-INDEPENDENT GLUCOSE-TRANSPORT ACTIVITY

Unweighting of the rat soleus by tail-cast suspension results in incre ased insulin action on stimulation of glucose transport, which can be explained, at least in part, by increased insulin binding and enhanced glucose transporter protein levels. Glucose transport is also activat ed by an insulin-independent mechanism stimulated by in vitro muscle c ontractions or hypoxia. Therefore, the purpose of this study was to de termine if soleus unweighting leads to an enhanced response of the ins ulin-independent pathway for stimulation of glucose transport. The hin dlimbs of juvenile male Wistar rats were suspended bv a tail-cast syst em for 3 or 6 days. Glucose transport activity in isolated soleus stri ps (approximately 18 mg) was then assessed by using 2-deoxy-[1,2-H-3]g lucose (2-DG) uptake. Insulin (2 mU/ml) had a progressively enhanced e ffect on 2-DG uptake after 3 and 6 days of unweighting (+44 and +72% v s. control, respectively; both P < 0.001). At these same times, there was no difference between groups for activation of 2-DG uptake by maxi mally effective treatments with contractions (10 tetanuses), hypoxia ( 60 min), or caffeine (5 mM). These results indicate that the enhanced capacity for stimulation of glucose transport after soleus unweighting is restricted to the insulin pathway, with no apparent enhancement of the insulin-independent pathway.