title: Cardiac muscle ultrastructure and cyclic AMP reactions to altered gravity conditions.
abstract: 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.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism*; D005260:Female; D006112:Gravitation; D008297:Male; D009124:Muscle Proteins / Q000378:metabolism; D009132:Muscles / Q000378:metabolism / Q000648:ultrastructure*; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism / Q000648:ultrastructure*; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D009124:Muscle Proteins; D000242:Cyclic AMP; D011494:Protein Kinases; D010727:Phosphoric Diester Hydrolases; D000262:Adenylyl Cyclases