Hyperthyroid myopathy. Intracellular electrophysiological measurements in biopsied human intercostal muscle.
Morphological and electrophysiological studies were performed on intercostal muscle biopsies from 2 thyrotoxic patients. The diseased fibers had numerous areas of subsarcolemmal glyogen accumulations and abnormal membranous projections. Both Type I and Type II muscle fibers were atrophied.  Diseased fibers were substantially depolarized and when artifically hyperpolarized showed earlier inactivation of the sodium conductance as a function of membrane potential, and a critical depolarization potential more depolarized than in normal fibers. When stimulated at 20 pulses/sec, or faster, the diseased fibers could not generate normal action potentials due to membrane depolarization and the appearance of a marked after-hyperpolarization. Muscle weakness associated with hyperthyroidism is attributed to the reduced membrane excitability.
D000328:Adult; D004558:Electric Stimulation; D004594:Electrophysiology; D005260:Female; D006003:Glycogen / Q000378:metabolism; D006651:Histocytochemistry; D006801:Humans; D006980:Hyperthyroidism / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D066298:In Vitro Techniques; D007366:Intercostal Muscles / Q000378:metabolism / Q000503:physiopathology* / Q000648:ultrastructure; D008297:Male; D008564:Membrane Potentials; D008854:Microscopy, Electron
D006003:Glycogen