Journal of Applied Physiology, Vol 73, Issue 2 101S-106S, Copyright © 1992 by American Physiological Society
Photoaffinity labeling of regulatory subunits of protein kinase A in cardiac cell fractions of rats
M. I. Mednieks, I. Popova and R. E. Grindeland
University of Illinois, Chicago 60612.
The regulatory (R) subunits of adenosine 3',5',-cyclic
monophosphate-dependent protein kinase were measured by photoaffinity
labeling in heart tissue of rats flown on COSMOS 2044. Densitometric
analyses showed a significant decrease of RII subunits in the particulate
cell fraction extract (S2; P less than 0.05 in all cases) when extracts of
tissue samples from vivarium controls were compared with those from flight
animals. Photoaffinity labeling of the soluble fraction (S1) was unaffected
by spaceflight or any of the simulation conditions. This was previously
observed in heart muscle of rats flown on Spacelab 3 and COSMOS 1887
missions. A change in either the number or reactivity of the R subunits
apparently results from some aspect of spaceflight. Proteins of the S2
fraction constitute a minor (less than 10%) component of the total, whereas
the S1 fraction contained most of the cell proteins. No changes were seen
when total incorporation of photoaffinity label was calculated on the basis
of adrenal gland weights. A negative correlation resulted on comparison of
controls with flight, synchronous control, and a tail-suspended simulation
group of animals when incorporation of total counts due to azido labeling
was based on body weights. Environmental factors that influence organismic
responses may alter individual hormonal responses and may be reflected on
the molecular level of organization. Conversely, changes in a relatively
minor aspect of adenosine 3',5'-cyclic monophosphate-mediated reactions may
be representative of a metabolic effect on an organismic level.
