ENERGY-RICH PHOSPHATES IN SLOW AND FAST HUMAN SKELETAL-MUSCLE

We investigated the relationship between energy-rich phosphate content and muscle fiber-type composition in human skeletal muscle using a co mbination of P-3l-nuclear magnetic resonance spectroscopy (NMR), histo chemical, and biochemical analyses of muscle biopsies. Localized P-31 spectra were collected simultaneously from the predominantly slow-twit ch soleus muscle and the mixed (fast-twitch and slow-twitch) medial an d lateral gastrocnemius muscles, using B-1-insensitive Hadamard Spectr oscopic Imaging. Biopsy samples were taken from the soleus and lateral gastrocnemius muscles before NMR investigation and analyzed for fiber type composition and succinic dehydrogenase (SDH) activity. Fiber-typ e composition was determined based both on myofibrillar actomyosin ATP ase activity combined with cross-sectional area and on myosin heavy-ch ain composition. Localized spectroscopy demonstrated a significantly ( P < 0.001) higher P-i/phosphocreatine ratio in the soleus muscle (0.15 +/- 0.01) compared with the medial (0.12 +/- 0.01) and lateral (0.10 +/- 0.0) gastrocnemius. However, in vitro analysis of muscle biopsies showed only a moderate relationship between the basal phosphate conten t and myofibrillar actomyosin ATPase-based fiber-type composition and SDH activity, respectively.