AJP - Endocrinology and Metabolism, Vol 272, Issue 1 E118-E125, Copyright © 1997 by American Physiological Society
Contraction-induced intracellular signals and their relationship to muscle GLUT-4 concentration
B. B. Yaspelkis 3rd, A. L. Castle, R. P. Farrar and J. L. Ivy
Department of Kinesiology, University of Texas at Austin 78712, USA.
This investigation used a model of increased skeletal muscle contractile
activity to evaluate whether the adenylate cyclase-adenosine 3',5'-cyclic
monophosphate (cAMP) pathway and/or the high-energy phosphate state of the
muscle might be temporally related to the contraction-induced increase in
skeletal muscle GLUT-4 protein concentration. Plantaris and gastrocnemius
muscles of Sprague-Dawley rats were subjected to 3, 7, 14, or 28 days of
chronic low-frequency electrical stimulation (10 Hz, 24 h/day). GLUT-4
protein concentration was slightly reduced after 3 days of electrical
stimulation, similar to control values at 7 days and significantly elevated
above control at 14 days (53%, P < 0.05) and 28 days (338%, P < 0.05)
of stimulation. ATP, creatine phosphate, creatine, and P, were inversely
related to GLUT-4 protein concentration. Adenylate cyclase activity
increased with electrical stimulation and was significantly related to the
increased GLUT-4 protein. cAMP was significantly increased at 14 days of
stimulation and remained elevated through 28 days. 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 GLUT-4 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 GLUT-4 protein
concentration.
