Dystrophin, vinculin, and aciculin in skeletal muscle subject to chronic use and disuse

Dystrophin is a subsarcolemmal protein that interacts with cytoskeletal actin and a glycoprotein complex in the plasma membrane. One potential function of dystrophin is its ability to Is stabilize the sarcolemmal membrane during muscle contraction. We hypothesized 1) that chronic muscle use and disuse would alter the expression of dystrophin as a compensatory mechanism designed to prevent muscle damage, and 2) that other subsarcolemmal cytoskeletal proteins (vinculin, M-vinculin, aciculin 60/63 kDa) that colocalize with dystrophin in muscle adherens junctions would be changed in parallel. Chronic muscle use induced by voluntary running or 10-Hz chronic stimulation did not alter dystrophin levels in rat muscle. In contrast, muscle disuse induced by 6 d of microgravity, or 7 and 21 d of denervation, increased dystrophin levels by 1.8-, 1.9- and 3.2-fold, respectively. Thus, this increase in dystrophin levels appears to be dependent on the duration of muscle disuse, independent of the presence of the nerve. Denervation also induced 3.3-fold increases in vinculin and aciculin 60 kDa, in parallel with dystrophin. However, in contrast to its effects on dystrophin, chronic stimulation increased the levels of vinculin and aciculin 60 kDa by 3.4- and 6.4-fold, respectively . Thus, both the removal and the augmentation of muscle activity resulted in increases of these two cytoskeletal proteins. The data indicate that the concentrations of these proteins are independently regulated. They further indicate that chronic muscle use is not a stimulus for the induction of dystrophin levels, suggesting that normal levels are sufficient for the protective effect on the sarcolemma that dystrophin may confer. The results reveal an interesting area of muscle plasticity, and the adaptation observed may have profound implications for the structure and function of skeletal muscle responding to changes in contractile activity.