Differences in enzyme efflux from dystrophic mouse skeletal muscle and heart

The efflux of the enzymes, creatine kinase (CK) and lactate dehydrogenase (LDH) from isolated normal and dystrophic mouse (C57BL/6J-dy) skeletal muscle and heart has been studied. Older (5-9 months) dystrophic mouse triceps contained only 63% of normal CK. At 3.5-10 weeks, dystrophic gastrocnemii had 72% and 61% of normal for males and females, respectively. By 5-7 months, the levels dropped to only 26% and 15% of normal. When skeletal muscle efflux was normalized to enzyme content, dystrophic muscle was not significantly different from normal for the first three hours, and was lower than normal in the 3-5 hour period. This was true for both triceps and gastrocnemius. Similarly, no difference in LDH efflux from gastrocnemius was seen between control and dystrophic mice. In contrast, there was no difference in enzyme concentration of normal and dystrophic hearts. Despite this, hearts from dystrophic mice had a higher efflux of both CK and LDH in the first three hours, but not beyond. The results indicate that under the conditions of these studies, dystrophic skeletal muscle was not, but heart was, more permeable to muscle enzymes than normal muscle.