Ej. Henriksen et Ls. Ritter, EFFECT OF SOLEUS UNWEIGHTING ON STIMULATION OF INSULIN-INDEPENDENT GLUCOSE-TRANSPORT ACTIVITY, Journal of applied physiology, 74(4), 1993, pp. 1653-1657
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.