Altered glycogen synthase and phosphorylase activities in skeletal muscle of tetraplegic patients

Despite marked differences in both the extent of physical activity and in m uscle metabolism and structure between tetraplegic and control subjects, th e glycogen content in the skeletal muscle of both groups is similar. We det ermined whether this similarity could be explained by the activities of key enzymes of glycogen metabolism. Muscle biopsies were analysed for glycogen synthase (GS) and glycogen phosphorylase (GP) activities, as well as for m etabolites. Glycogen content did not differ significantly between the two g roups. Total glycogen synthase activity was reduced by almost 60 % in tetra plegics (P < 0.01), whereas total phosphorylase activity did not differ bet ween groups. GS fractional activity did not differ between groups, whereas phosphorylase fractional activity (<minus/plus> AMP) was significantly high er in the tetraplegics (0.08 +/- 0.01, control; 0.25 +/- 0.02, tetraplegics ; P < 0.001), Neither uridine diphosphate (UDP)-glucose nor glucose 6-phosp hate (G-6-P) content in muscle differed significantly between groups. These data demonstrate that, in tetraplegics, muscle glycogen content is preserv ed despite decreases in GS activity and increases in phosphorylase fraction al activity. Muscle paralysis has differential effects on the activities of GS and GP.