[Localization of acid organelles in frog skeletal muscle fibers]

By means of fluorescent and phase-contrast microscopy the distribution of acid membrane organelles in normal and vacuolated frog skeletal muscle fibers has been studied. The vacuolation of the T-system was produced by loading and subsequent removal of glycerol (80-110 mM), or it appeared as a result of Zenker's necrosis. Acridine orange (AO) was used as a marker for acid intracellular compartments. AO accumulated in granules localized near the nuclear poles (more seldom around the nucleus)' and in the intermyofibrillar spaces. Typically the AO granules make up short longitudinal chains or regular pairs, where the distances between neighboring granules are short-dated to sarcomere lengths. Almost all granules emit in red, but about one third of them simultaneously emit in green, which is characteristic of AO monomers. In the vicinity of necrotic boundary or under the influence of brefeldin A, a green component of fluorescence appears in most granules. Treatment with monensin leads to granule disappearance. Vacuoles accompanying the glycerol treatment or developing of necrosis do not accumulate AO and exert no effect on the localization of AO-granules. The nature of cellular organelles accumulating AO in skeletal muscle fibers is discussed.