Quantitative freeze-fracture electron microscopic study of muscle plasma membrane of experimental anoxic myopathy.

The numerical change of intramembranous particles (IMP) and square arrays (SA) was investigated in the muscle plasma membrane after anoxia. The proximal portion of the hind limb of Wistar rats weighing 250-350 g was strongly tied with steel wire. The contralateral hind limb was served as control. After 3 and 6 h, the extensor digitorum longus (EDL) muscles of both control and anoxic groups were studied by freeze-fracture electron microscopy. The findings of anoxic EDL plasma membrane included the presence of band-like or patchy form particle free areas with the tendency to increase from 3 to 6 h and the preservation of SA even after 6 h of anoxia. However, the IMP and caveolae densities between control and anoxic groups were not statistically different. The group median densities of SA/micron2 of control P face were 4.9 with midrange of 2.2-9.7 and 7.1 with mid-range of 2.7-10.9 after 3 and 6 h; whereas those of anoxic P face were 6.0 with mid-range of 1.8-8.2 (P greater than 0.1) and 6.9 with mid-range of 3.3-13.5 (P greater than 0.1), respectively. These changes are quite different from those of muscle plasma membrane in Duchenne muscular dystrophy.