EFFECT OF 17 DAY BEDREST ON THE ENZYME AND METABOLITE PROFILE OF THE SLOW TYPE I FIBER 870

Abstract

The purpose of this study was to determine if the bedrest model of weightlessness affects the enzyme and substrate profile in human skeletal muscle. Freeze-dried single fibers were prepared from human soleus biopsies before and after 17 days of bedrest. Each fiber was cut into three pieces for gel typing, metabolite and enzyme assay. Standard and digested fiber solutions were stored under oil in Teflon racks. Assays were conducted using fluorometric biochemical techniques based on pyridine nucleotide specific reactions followed, if necessary, by enzymatic cycling. The results for the slow type I fibers are shown in the table whereβOAC = β-hydroxyacyl-CoA dehydrogenase, CAT = carnitine acetyl transferase, CS = citrate synthase, and GP = glycogen phosphorylase. The oxidative enzymes (βOAC & CS) showed a small but non-significant decline, while the FFA transport enzyme CAT was unaffected. Importantly, bedrest induced an ≈ 1.5-fold increase in glycogen, and the enzymes involved in glucose and glycogen metabolism (hexokinase & GP) also significantly increased. These data are consistent with the hypothesis that both bedrest and weightlessness increase type I fiber dependence on carbohydrate metabolism.