Injury and repair of the soleus muscle after electrical stimulation of thesciatic nerve in the rat

To study injury and subsequent changes in skeletal muscles, the rat sciatic nerve was electrically stimulated at 50 Hz and muscle contraction was indu ced for 30 min. Muscle damage was classified into five types (hypercontract ion, hyperstretching, Z band disorders, misalignment of myofilament and reg ions of scarce myofilaments) by electron microscopy and quantified by ultra structural assessment. After electrical nerve stimulation, the percentages of the injured areas of the soleus muscle were 18.8 +/- 15.8% (mean +/- SD) at 0 h, 9.7 +/- 1.0% at 6 h, 22.0 +/- 23.6% at 12 h, 13.1 +/- 3.2% at 24 h , 4.9 +/- 6.0% at 3 days and 0.5 +/- 0.4% at 7 days. At 0 h, the vast major ity of ultrastructural alterations were sarcomere hypercontraction. At 6 h, hypercontraction was not recognizable and sarcomere hyperstretching and Z band disarrangement constituted the major findings. At 12 h, when the injur y reached its maximum, myofilament disorganization and hyperstretching were predominant. At 24 h or afterwards, the injury began to decrease and recov ered to almost normal conditions by 7 days. There were very few necrotic mu scle fibers in all specimens. It is considered that the muscle lesions in t he present study were reversible, and recovered through changes in various types of sarcomere alterations. Z band streaming and free ribosomes were fr equently found at 12 and 24 h, which may indicate repair processes rather t han newly formed lesions.