Analysis of muscle proteins in acute quadriplegic myopathy.

We investigated the changes of muscle proteins in acute quadriplegic myopathy (AQM) using immunohistochemistry and stoichiometry. Cases of AQM were observed in which it was difficult to type muscle fibers with adenosine triphosphatase staining in biopsied muscle. Well-defined typing of these cases was possible by performing immunofluorescent staining using slow and fast skeletal troponin I (TnI) antibodies. By this means, small angular fibers were shown to be fast skeletal muscle, and myosin was absent from these muscle fibers. Actin and tropomyosin were maintained. Muscle protein ratios were determined by stoichiometry following sodium dodecyl sulfate-polyacrylamide gel electrophoresis of AQM myofibril specimens from four subjects. The myosin heavy chain/actin ratio was significantly decreased compared with a normal control group and other neuromuscular diseases. These pathologic findings returned to normal during recovery from AQM. Thus, myosin selectively decreases, whereas actin and regulatory proteins located above it are maintained during AQM.