The Use of Acridine Orange as a Lysosomal Marker in Rat Skeletal Muscle

'The uptake of vital dyes by lysosomes (1, 2) has permitted the microscopic observation of these subcellular organelles in living cells (3) and tissue homogenates (4) . Acridine orange (3 , 6-bis-dimethylaminoacridine), a fluorescent metachromatic dye, has been shown to concentrate within lysosomes, causing them to appear as bright orange granules in fluorescence microscopy (5-7) . We have observed these granules in fresh frozen sections of rat skeletal muscle and have determined their subcellular distribution by quantitating the dye with spectrophotofluorometry. Our technique demonstrates the use of acridine orange as a nonenzymatic marker for lysosomes in tissue fractionation studies.