Decreased osmotic stability of dystrophin-less muscle cells from the mdx mouse 
 Human X-linked Duchenne and Becker muscular dystrophies are due to defects in dystrophin, the product of an exceptionally large gene.
 Although dystrophin has been characterized as a spectrin-like submembranous cytoskeletal protein, there is no experimental evidence for its function in the structural maintenance of muscle.
 Current hypotheses attribute necrosis of dystrophin-less fibres in situ to mechanical weakening of the outer membrane, to an excessive influx of Ca2+ ions, or to a combination of these two mechanism, possibly mediated by stretch-sensitive ion channels.
 Using hypo-osmotic shock to determine stress resistance and a mouse model (mdx) for the human disease, we show that functional dystrophin contributes to the stability of both cultured myotubes and isolated mature muscle fibres.
