Journal of Applied Physiology, Vol 73, Issue 2 66S-73S, Copyright © 1992 by American Physiological Society
Effects of microgravity and tail suspension on enzymes of individual soleus and tibialis anterior fibers
M. M. Chi, R. Choksi, P. Nemeth, I. Krasnov, E. Ilyina-Kakueva, J. K. Manchester and O. H. Lowry
Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110.
Selected enzymes of energy metabolism were measured in random individual
fibers of soleus and tibialis anterior (TA) muscles from rats exposed for 2
wk to spaceflight (F) aboard COSMOS 2044 or tail suspension (T) and from
synchronous controls. Average size of soleus fibers (dry weight per unit
length) was reduced 37% in F and T fibers; there was little change in TA
fibers. Enzyme changes were more pronounced in soleus than in TA fibers.
Three enzymes characteristic of fast-twitch muscles, pyruvate kinase,
glycerol-3-phosphate dehydrogenase, and 1-phosphofructokinase, were
elevated in F and T soleus fibers, but changes in phosphofructokinase were
not statistically significant. 3-Ketoacid-CoA transferase, characteristic
of slow-twitch muscles, did not change significantly in either F or T
fibers. Hexokinase, usually moderately higher in slow- than in fast-twitch
muscles, increased markedly in both F and T fibers. In TA fibers analyzed
for hexokinase, malate dehydrogenase, phosphohexoisomerase, and pyruvate
kinase, only hexokinase and malate dehydrogenase showed significant
changes. Hexokinase increased 83% in one of two T muscles. Enzyme data for
TA fibers typed by myosin adenosinetriphosphatase were more informative:
phosphofructokinase, phosphorylase, and glycerol-3-phosphate dehydrogenase
were increased in type IIb fibers of either F or T muscles or both. Malate
dehydrogenase was not changed in fibers of any type in either F or T
muscle.
