The Journal of General Physiology, Vol 79, 147-166, Copyright © 1982 by The Rockefeller University Press
Chemical energetics of slow- and fast-twitch muscles of the mouse
MT Crow and MJ Kushmerick
The energy utilization associated with contraction was measured in isolated
slow- and fast-twitch muscles of the mouse at 20 degrees C. The extent of
this utilization was estimated from either the extent of high-energy
phosphate splitting occurring during contraction (the initial chemical
change, delta approximately P init) or from the extent of recovery
resynthesis calculated from the observed oxygen consumption and lactate
production occurring during the recovery period (recovery chemical
resynthesis, delta approximately P rec). For short tetani, the cost to
maintain isometric tension in the fast-twitch extensor digitorum longus
(EDL) was approximately threefold greater than that in the slow-twitch
soleus. With prolonged stimulation, however, the energy cost in the EDL
diminished so that after 12 s of stimulation, the energy cost in the EDL
was only 50% greater than that of the soleus. For both the slow-twitch
soleus and the fast-twitch EDL and for all tetanus durations (up to 15 s),
the extent of the initial chemical change was identical with the amount of
recovery chemical resynthesis, showing that a biochemical energy balance
existed in these muscles.
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