Functional deficits in medial gastrocnemius grafts in rats: relation to muscle metabolism and beta-AR regulation.

Abstract

This study tested the hypothesis that alterations in the metabolic integrity of grafted muscle contribute to its diminished ability to sustain power. Compared with control muscles, muscles studied 120 days after the grafting procedure had lower specific force and sustained power. The sustained power protocol resulted in a depletion of muscle glycogen in control (83%) and grafted (85%) animals. Grafts had lower pre- and poststimulation glycogen, diminished citrate synthase activity, and greater hexokinase activity. No differences were observed in phosphofructokinase activity, glucose transporter GLUT-4 content, fiber type, beta-adrenergic-receptor (beta-AR) density, or binding affinity. Isoproterenol-stimulated adenylyl cyclase activity was lower in grafted vs. control muscle, suggesting an uncoupling of the beta-AR-effector complex. Thus the diminished ability of the grafted muscle to sustain power may be explained, in part, by a decrease in energy available from glycogen stores and/or a decrease in oxidative capacity.