Several Dystrophin-glycoprotein Complex Members Are Present in the Crude Surface Membranes of Mdx Mouse Muscle While Sodium Dodecyl Sulphate Invisible in Kcl-washed Microsomes

The dystrophin-glycoprotein complex (DGC) is a large trans-sarcolemmal complex that provides a linkage between the subsarcolemmal cytoskeleton and the extracellular matrix. In skeletal muscle, it consists of the dystroglycan, sarcoglycan and cytoplasmic complexes, with dystrophin forming the core protein. The DGC has been described as being absent or greatly reduced in dystrophin-deficient muscles, and its lack is considered to be involved in the dystrophic phenotype. Such a decrease in the DGC content was observed in dystrophindeficient muscle from humans with muscular dystrophy and in mdx mice (X-linked Muscular Dystrophy). These deficits were observed in total muscle homogenates and in partially membrane-purified muscle fractions, the so-called KCl-washed microsomes. Here, we report that most of the proteins of the DGC are actually present at normal levels in the mdx mouse muscle plasma membrane. The proteins are detected in dystrophic animal muscles when the immunoblot assay is performed with crude surface membrane fractions instead of the usually employed KCl-washed microsomes. We propose that these proteins form SDS-insoluble membrane complexes when dystrophin is absent.