Shortening heat in slow- and fast-twitch muscles of the rat.
Holroyd, Sean M., Colin L. Gibbs, and Anthony R. Luff.
Department of Physiology, Monash University, Clayton VIC 3168,
AUSTRALIA
APStracts 2:0245C, 1995.
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, at the onset of a
summated twitch from different initial lengths. At the end of the
shortening period the muscle contracted isometrically: the stress and
associated heat production were recorded. This heat:stress data was
compared to 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.
Received 2 February 1995; accepted in final form 27 June 1995.
APS Manuscript Number C64-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.