AJP - Cell Physiology, Vol 270, Issue 1 C293-C297, Copyright © 1996 by American Physiological Society
Shortening heat in slow- and fast-twitch muscles of the rat
S. M. Holroyd, C. L. Gibbs and A. R. Luff
Department of Physiology, Monash University, Clayton, Victoria, Australia.
Shortening heat has been reported in several amphibian skeletal muscles. In
this investigation, shortening heat has been investigated in both soleus
and extensor digitorum longus (EDL) muscles of young rats. The procedure
involved shortening the muscles through two different distances, at near
maximum velocity and at the onset of a summated twitch from different
initial lengths. At the end of the shortening period, the muscle contracted
isometrically, and the stress and associated heat production were recorded.
These heat-stress data were compared with heat-stress data of isometric
twitches at different initial lengths. There was a parallel upward shift in
energy output when shortening occurred, indicating the presence of a
shortening heat. Shortening heat increased with the distance shortened in
soleus, but this was not the case for EDL. The values for the shortening
heat coefficient for both muscle types are slightly higher than those
reported for amphibian skeletal muscle and suggest that shortening heat is
a significant component of the energy output of mammalian skeletal muscle.
