Aj. Baker et al., ENERGY USE BY CONTRACTILE AND NONCONTRACTILE PROCESSES IN SKELETAL-MUSCLE ESTIMATED BY P-31-NMR, The American journal of physiology, 266(3), 1994, pp. 30000825-30000831
The goal of this study was to separately determine ATP use by contract
ile and noncontractile processes in stimulated skeletal muscle. ATP us
e by tetanically stimulated bullfrog semitendinosus muscle was monitor
ed at room temperature with in vivo P-31-nuclear magnetic resonance. O
xidative phosphorylation was inhibited by cyanide, and ATP use could t
herefore be calculated by accounting for ATP derived from the creatine
kinase (CK) reaction (measured from decreases in phosphocreatine) and
from glycolysis (estimated from decreases of intracellular pH). In un
fatigued muscles stimulated at optimal length for force production, to
tal ATP utilization (representing both contractile and noncontractile
processes) was 2.5 +/- 0.09 (SE) mM/s (n = 6; 53% ATP from glycolysis,
47% from CK). In separate experiments, cross-bridge interactions betw
een actin and myosin filaments were eliminated by increasing sarcomere
length; therefore, with stimulation, residual ATP use reflected only
noncontractile processes. In stimulated stretched muscles, ATP utiliza
tion was reduced compared with unstretched muscles to 1.07 +/- 0.08 mM
/s (61% ATP from glycolysis, 39% from CK). These findings suggest that
, during contraction near optimum length, a large proportion (similar
to 43%) of ATP is used by noncontractile processes, with more ATP deri
ved from glycolysis than from CK.