[3H]Ouabain binding in normal and dystrophic mouse skeletal muscles and the effect of age

The numbers of Na+-K+ ATPase sites in skeletal muscles of normal and dystrophic mice between 3 and 17 months of age have been estimated using [3H]ouabain binding assays. In normal mice, at all ages, slow twitch muscle, soleus (SOL), bound significantly more [3H]ouabain than fast-twitch muscle, extensor digitorum longus (EDL). [3H]Ouabain binding did not alter in either SOL or EDL from normal mice over the age range studied. The numbers of Na+-K+ ATPase sites did alter in muscles taken from dystrophic mice (C57BL/6J dy2J/dy2J). In EDL there was an increase and in SOL a decrease in [3H]ouabain binding. This may be related to a change in muscle fibre metabolism from glycolytic to oxidative or to an altered activity pattern. Increasing age resulted in a progressive reduction in [3H]ouabain binding of both SOL and EDL from dystrophic mice. Part of this reduction may be only apparent and due to an increase in connective tissue composition of dystrophic muscles. A limited study of muscles from neonate dystrophic mice indicated that abnormal [3H]ouabain binding was not present in EDL before two weeks of age.