Electron Microscopic Studies of the T-System—The Effects of Hyperosmolar Glycerol and Dantrolene Sodium on Mammalian Muscles

Electron microscopic studies of the T-systems in mammalian muscles were performed to investigate the effects of hyperosmolar glycerol solution and dantrolene sodium. The results indicate that in mammalian muscles the terminal cisterns of the sarcoplasmic reticulum seem to be the site of morphological changes which occur when the muscle specimens were transferred from the hypertonic glycerol solution to isotonic washing solution. When the muscle specimen was further exposed to dantrolene solution, the above changes were intensified. The changes of the terminal cisterns of SR were characterized by prominent vacuolar changes and the T-tubules were pressed and narrowed by those vacuoles secondarily. The glycerol and dantrolene technique did not cause any electron microscopic changes in the sarcolemma, myofibrils, nor Z-discs, and selective changes in the T-system, i.e. at the terminal cisterns of SR were demonstrated. This technique, excitation-contraction uncoupling, abolishes isometric twitch tension up to 99.7% and serves for the purpose of prolonged intracellular recordings of mammalian muscles without movement induced artifacts.