Glut-4 protein and citrate synthase activity in distally or
proximally denervated rat soleus muscle.
Fogt, Donovan L., Michael J. Slentz, Marc E. Tischler, and Erik J.
Henriksen.
Departments of Biochemistry and of Physiology, University of
Arizona College of Medicine, Tucson, AZ 85721-0093
APStracts 3:0377R, 1996.
The potential role of neurotrophic factors in the decline of glucose
transporter (GLUT-4) protein levels and citrate synthase (CS)
activity was studied by comparing distally with proximally denervated
juvenile rat soleus muscle. Severing of the tibial nerve produced
distal (long stump) or proximal (short stump) denervation,
respectively. GLUT-4 levels and CS activities were measured at 24 h
intervals for up to 96 h after denervation. No differences were
observed in GLUT-4 or CS activity between soleus muscles left with
short or long nerve stumps at any time point. However, within just 24
h, denervation decreased (P < 0.05) GLUT-4 and CS (67.4 +/-
3.3% and 63.4 +/- 1.7% of innervated control values, respectively).
Both parameters continued to decline up to 96 h (44.4 +/- 3.1% and
48.7 +/- 4.0%, respectively). There was a significant correlation
between the GLUT-4 protein level and CS activity over this 96 h
period of denervation (r=0.653, P<0.001). A similar response
in the 24 h denervated soleus of adult rats was observed. In
contrast, 24 h denervation of red gastrocnemius (type IIa fibers)
left with a long nerve stump resulted in a prevention of the decline
of GLUT-4 and CS seen in red gastrocnemius left with a short nerve
stump, both in juvenile and adult animals. These results suggest
that, unlike type IIa muscles, the decline in GLUT-4 level and
citrate synthase activity in type I soleus muscle following
denervation results from a lack of coordinated electrical activity,
but likely does not involve a neurotrophic agent. These results also
support the hypothesis that there is co-regulation of decreased
expression of GLUT-4 protein and CS activity in this model of reduced
neuromuscular activity.
Received 29 March 1996; accepted in final form 17 October 1996.
APS Manuscript Number R188-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996