Difference in the expression pattern of dystrophin on the surface membrane between the skeletal and cardiac muscles of mdx carrier mice.

We examined the expression of dystrophin by immunohistochemical and immunoblot analyses in the skeletal and cardiac muscles of Xmdx/X+ heterozygous mice, which were obtained by mating male mdx mice (Xmdx/Y) with female wild type mice (X+/X+). Dystrophin was expressed on the surface membrane in both muscles, but the mode of expression was different between the two muscles. In cardiac muscle, dystrophin positive and negative cells were present in roughly equal numbers intermingled in a mosaic pattern; this was considered to reflect the random inactivation of X-chromosomes in early development. In skeletal muscle, most of the surface membrane was dystrophin positive. There were little signs of fiber necrosis or regeneration, and serum creatine kinase levels were normal. We are at present of opinion that the predominance of dystrophin-positive area in skeletal muscle is due to intracellular diffusion of dystrophin.