Changes in elemental composition of single muscle fibers following tenotomy of the rat soleus muscle

Cores were produced in type 1 muscle fibers by tenotomy of rat soleus muscle. The morphology and histochemistry of the muscle fibers was established by light microscopy on cryostat sections stained for hematoxylin‐eosin or myofibrillar ATPase and on semithin plastic sections. The ultrastructure was visualized on thin plastic sections. On 6 μm of freeze‐dried cryosections, energy dispersive X‐ray microanalysis was performed on muscle fibers visualized in the scanning transmission mode of electron microscopy. This procedure permitted quantification of different intracellular elements such as sodium (Na), chlorine (CI), potassium (K), magnesium (Mg), sulphur (S), and phosphorus (P). Spectra from core fibers could easily be compared with those of normal fibers. A conspicuous finding was an increased Na and CI content and a decreased K content in core fibers compared to normal fibers. It is known that core fibers produced after tenotomy exhibit distinct changes in plasma membrane morphology similar to that found in Duchenne muscular dystrophy (DMD). The results in this study point to a change in normal intracellular ion composition which could be a result of a deficiency of mechanisms maintaining normal membrane ion gradients.