Quantitative freeze-fracture electron-microscopic analysis of muscle plasma membrane of bupivacaine-induced myopathy.

Rat extensor digitorum longus (EDL) muscles exposed to bupivacaine for 15 min were studied by freeze-fracture electron microscopy. In the bupivacaine-treated and control muscle plasma membranes we studied (1) caveolar density, (2) orthogonal array density, (3) orthogonal array subunit particle density per one orthogonal array and (4) non-array intramembranous particle density. We found a conspicuous decrease of caveolar density and a statistically significant decrease of non-array particle density. Although the orthogonal array density showed a tendency to decrease, the orthogonal array subunit particle density per one orthogonal array was not affected. We also noted aggregation of intramembranous particles and orthogonal arrays. The findings differed from those seen in Duchenne muscle plasma membrane in some respects.