Electron Microscopic Studies on the Mechanism of Vital Stain, as Compared with That of Phagocytosis

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Abstract
Electron microscopic observations of vital stain with acid (carmine and trypan blue) and basic (Janus green and neutral red) dyes were described and discussed. Vitally stained granules originate from the non-specific cytoplasmic granules: some of them preexist prior to, and the others are newly formed at the time of dye stuff invasion into the cytoplasm. Dye stuffs are segregated within these granules in high concentration. Such granules are designated as segresomes, and characterized by their single limiting membrane, diffuse internal matrix and lipoprotein masses often observed within them. The ultrastructure of segresomes, however, is more or less modified according to the sorts of segregating cells and segregated materials as well as the dosis and fixability of the latter. Segresomes are formed in almost all cells under various conditions, and are designated by each author as lysosomes, mocrobodies, cytosomes, etc. Segresomes are formed not only against foreign materials of external origin, but also against various materials of internal origin such as pigments. Extracellular dye stuffs penetrate the surface membrane of cell or limiting membrance of intracytoplasmic vacuoles to enter into the cytoplasm, and then are segregated within the segresomes, whereas particles as large as or larger than macromolecules remain, unless digestion occurs, within phagocytic or pinocytotic vacuoles. The upper limit of particulate size of substrates capable of penetrating cell membrance is assumed to be approximately 30A. Acid dye stuffs do not enter, in general, into the cells, because dye stuffs as anions can not penetrate the cell membrane on account of the highly negative charge of the latter. Reticuloendothelial cells and some others, however, can uptake acid dyes after a long time because of only a weakly negative (nearly neutral) charge of the cell membrane of these cells. Phagocytosis, pinocytosis and vital stain (segregation) are performed by cells in close connection with each other, although these are fundamentally different phenomena.