EFFECT OF CHRONIC ELECTRICAL STIMULATION AND ??-GPA DIET ON MUSCLE GLUT4 PROTEIN CONCENTRATION 1291

Abstract

The present study investigated whether alterations in the muscle high energy phosphate state initiates the contraction-induced increase in skeletal muscle GLUT4 protein concentration. Sprague-Dawley rats were provided either a normal (N) or a 2% β-guanidinoproprionic acid (β-GPA) diet for 8 wk and then the gastrocnemius of one hindlimb was subjected to 0, 14 or 28 d of chronic (24 h/d) low-frequency electrical stimulation (10 Hz). The β-GPA diet, in the absence of electrical stimulation, significantly reduced ATP, creatine phosphate, creatine and inorganic phosphate and elevated GLUT4 protein concentration by 60% (P<0.05) without altering adenylate cyclase activity or cAMP concentration. Following 14 d of electrical stimulation, GLUT4 protein concentration was elevated above non-stimulated muscle in both groups but was significantly more elevated (P<0.05) in the β-GPA group(99.3±5.5% heart standard, β-GPA vs. 65.3±8.4% heart standard, N). Concurrent with this greater rise in GLUT4 protein concentration was a greater decline in the high energy phosphates and a greater rise in cAMP. After 28 d of electrical stimulation, GLUT4 protein concentration and cAMP stabilized and was not different between treatments. However, the high energy phosphates were significantly higher in the N rats as opposed to theβ-GPA rats. These findings therefore suggest that a reduction in the high energy phosphates initiates the contraction-induced increase in muscle GLUT4 protein concentration, but that a rise in cAMP may protentiate this effect.