AJP - Regulatory, Integrative and Comparative Physiology, Vol 252, Issue 2 227-R232, Copyright © 1987 by American Physiological Society
Cardiac muscle ultrastructure and cyclic AMP reactions to altered gravity conditions
M. I. Mednieks, A. S. Fine, J. Oyama and D. E. Philpott
Morphological and biochemical analyses of heart muscle of rats subjected to
microgravity on Spacelab 3 (SL-3) flight and rats born and reared under
increased gravity (1.7 G) conditions were compared with 1-G controls.
Electronmicroscopic studies showed an increase in the number of lipid
droplets and in areas of glycogen storage. Distribution changes of
microtubules and cytoskeletal elements from both SL-3 and 1.7-G groups were
observed. The high Km cyclic AMP phosphodiesterase activity was lower (P
less than 0.05) in SL-3 heart muscle, and low Km activity was lower in
1.7-G males but was unaltered in females. Cyclic AMP-dependent protein
kinase (cA-PK) activity was decreased in subcellular fractions of heart
muscle of SL-3 animals. Recompartmentalization of cA-PK activity occurred
in particulate tissue fraction of 1.7-G animals (70.3% of total for 1.7 G
vs. 35.9% for controls). Phosphorylation of endogenous low-mobility
proteins increased in SL-3 heart-soluble fractions. Photoaffinity labeling
(18 h, 4 degrees C) decreased in type II cA-PK regulatory (R) subunits in
both SL-3 and in 1.7-G male heart tissue particulate fractions. The 1.7-G
female heart R subunit distribution did not differ from controls. These
findings indicate that in heart muscle altered gravity conditions
influenced physiological reactions similar to catecholamine-induced
receptor-mediated hormonal responses.
