[Pathophysiology of muscular atrophy due to disuse--with special reference to a single muscle fiber and its ultrastructure].
Immobilization muscule atrophy was experimentally induced by fixing one ankle joint with a K-wire in an extended position in rats. The animals were sacrificed at designated intervals to obtain the soleus muscle from the fixed (or disused) side and the free side; the muscles were weighed wet, evaluated (musculo) physiologically using a single-skinned muscle fiber method, and further examined histochemically and electron-microscopically. The wet weight of the disused soleus muscle was reduced to 54% of that of the healthy (used) muscle. According to classification by types of muscle fibers stained for ATPase, conversion of muscle fiber type, i.e., conversions of type 1 (red muscle) into type 2 (white muscle) was noted on the disused side, and similar findings were also observed by examination using a single skinned muscle fiber method. The maximal tension developed by the disused single muscle fiber was lower. This may be attributable to structural changes in the myofilament arrangement observed under an electron microscope. No abnormalities were found in calcium ion uptake by the sarcoplasmic reticulum. Under the present experimental conditions, it was clarified that the disuse atrophy of skeletal muscle induces not only reduction of muscle fibers in diameter but also their dedifferentiation and redifferentiation.
D000818:Animals; D007103:Immobilization; D008297:Male; D009119:Muscle Contraction; D009132:Muscles / Q000503:physiopathology / Q000648:ultrastructure*; D009133:Muscular Atrophy / Q000473:pathology*; D009929:Organ Size; D051381:Rats; D011919:Rats, Inbred Strains