Ultrastructure of toad (Bufo paracnemius) mast cells. Their alteration by compound 48/80

The fine structure of toad mast cells and their alteration by compound 48/80 is described. The specific cytoplasmic granules, which stain metachromatically with toluidine blue, seem to be of one type only, notwithstanding wide differences in their appearance. They are composed of an electron-dense, peripheral, lamellar component, and a matrix showing a particulate material embedded in a homogenous ground substance. The alterations induced by compound 48/80 were essentially restricted to mast cell granules. Eventually these disappeared leaving vacuoles filled with a flocculent material which was also found outside the cell. Solubilization of granule contents preceded secretion. Stimulated mast cells seemed to be morphologically intact, even those cells that showed very intense degranulation.