The incorporation of isotopes into proteins of normal and dystrophic mouse heart and skeletal muscle.

Studies are described of L-[3H-(G)]leucine and [5-3H]uridine incorporation into proteins in dystrophic mouse skeletal and heart muscle of the 129/Rej/dy Bar Harbor strain. The results show a remarkable difference in isotope incorporation in the 2 muscle types. While skeletal muscle in the dystrophic mouse shows a consistently high cytoplasmic incorporation of leucine and uridine respectively, the heart muscle shows a marked reduction of uptake in nuclear, myofibrillar, and cytoplasmic protein. These findings appear to suggest that in terms of protein synthesis the mouse heart is not affected at the age of 8 weeks by a recognizably similar dystrophic process to that in the skeletal muscle. Whilst our material showed no gross evidence of cardiomyopathy, cytomorphometric analysis of the dystrophic heart muscle is in keeping with an atrophic process. The possibility that this difference in protein synthesis pattern may be related to an embryologically different organogenesis of the heart and skeletal muscle altering the predystrophic synthesis pattern cannot be excluded.