Control of respiration and bioenergetics during muscle contraction.
(1)H-NMR experiments have determined intracellular O(2) consumption (Vo(2)) with oxymyoglobin (MbO(2)) desaturation kinetics in human calf muscle during plantar flexion exercise at 0.75, 0.92, and 1.17 Hz with a constant load. At the onset of muscle contraction, myoglobin (Mb) desaturates rapidly. The desaturation rate constant of approximately 30 s reflects the intracellular Vo(2). Although Mb desaturates quickly with a similar time constant at all workload levels, its final steady-state level differs. As work increases, the final steady-state cellular Po(2) decreases progressively. After Mb desaturation has reached a steady state, however, Vo(2) continues to rise. On the basis of current respiratory control models, the analysis in the present report reveals two distinct Vo(2) phases: an ADP-independent phase at the onset of contraction and an ADP-dependent phase after Mb has reached a steady state. In contrast to the accepted view, the initial intracellular Vo(2) shows that oxidative phosphorylation can support up to 36% of the energy cost, a significantly higher fraction than expected. Partitioning of the energy flux shows that a 31% nonoxidative component exists and responds to the dynamic energy utilization-restoration cycle (which lasts for only milliseconds) as postulated in the glycogen shunt theory. The present study offers perspectives on the regulation of respiration, bioenergetics, and Mb function during muscle contraction.
Chung
Youngran
Y
Department of Biological Chemistry, University of California, Davis, Davis, CA 95616-8635, USA.
Molé
Paul A
PA
Sailasuta
Napapon
N
Tran
Tuan Khanh
TK
Hurd
Ralph
R
Jue
Thomas
T
D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D019069:Cell Respiration / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology*; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009211:Myoglobin / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular; D010100:Oxygen / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism
D009211:Myoglobin; D010710:Phosphates; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D010100:Oxygen