FUNCTIONAL DEFICITS IN MEDIAL GASTROCNEMIUS GRAFTS IN RATS - RELATIONTO MUSCLE METABOLISM AND BETA-AR REGULATION

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