Dystrophin and utrophin complexed with different associated proteins in cardiac Purkinje fibres

Abnormal dystrophin expression is directly responsible for Duchenne and Bec ker muscular dystrophies. In skeletal muscle, dystrophin provides a link be tween the actin network and the extracellular matrix via the dystrophin-ass ociated protein complex. In mature skeletal muscle, utrophin is a dystrophi n-related protein localized mainly at the neuromuscular junction, with the same properties as dystrophin in terms of linking the protein complex. Utro phin could potentially overcome the absence of dystrophin in dystrophic ske letal muscles. In cardiac muscle, dystrophin and utrophin were both found t o be present with a distinct subcellular distribution in Purkinje fibres, i .e. utrophin was limited to the cytoplasm, while dystrophin was located in the cytoplasmic membrane. In this study, we used this particular characteristic of cardiac Purkinje f ibres and demonstrated that associated proteins of dystrophin and utrophin are different in this structure. We conclude, contrary to skeletal muscle, dystrophin-associated proteins do not form a complex in Purkinje fibres. In addition, we have indirect evidence of the presence of two different 400 k Da dystrophins in Purkinje fibres.