Contraction-induced intracellular signals and their relationship to
muscle glut4 concentration.
Yaspelkis, B. B., A. L. Castle, R. P. Farrar, and J. L. Ivy.
Exercise Physiology and Metabolism Laboratory, Department of
Kinesiology, The University of Texas at Austin, Austin, Texas
78712
APStracts 3:0193E, 1996.
This investigation used a model of increased skeletal muscle
contractile activity to evaluate whether the adenylate cyclase-cAMP
pathway and/or the high energy phosphate state of the muscle might be
temporally related to the contraction-induced increase in skeletal
muscle GLUT4 protein concentration. Plantaris/gastrocnemius muscles
of Sprague-Dawley rats were subjected to 3, 7, 14 or 28 d of chronic
low-frequency electrical stimulation (10 Hz, 24 h/d). GLUT4 protein
concentration was slightly reduced following 3 d of electrical
stimulation, similar to control values at 7 d and significantly
elevated above control at 14 d (53%, p<0.05) and 28 d (338%,
P<0.05) of stimulation. ATP, creatine phosphate, creatine and
inorganic phosphate were inversely related to GLUT4 protein
concentration. Adenylate cyclase activity increased with electrical
stimulation and was significantly related to the increased GLUT4
protein. cAMP was significantly increased at 14 d of stimulation and
remained elevated through 28 d. These results demonstrate that both
the adenylate cyclase-cAMP pathway and the high energy phosphate
state of the muscle are temporally related to elevations in skeletal
muscle GLUT4 protein concentration in response to chronic low
-frequency electrical stimulation and, as such, suggest that both may
comprise a component of the intracellular signal that regulates the
contraction-induced increase in skeletal muscle GLUT4 protein
concentration.
Received 22 April 1996; accepted in final form 28 August 1996.
APS Manuscript Number E201-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996