Photoaffinity labeling of regulatory subunits of protein kinase A in cardiac cell fractions of rats

Abstract

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.