HISTOCHEMICAL AND ULTRASTRUCTURAL STUDIES OF MAST-CELLS IN THE INTESTINAL-MUCOSA AND SKIN OF THE OPOSSUM DIDELPHIS-ALBIVENTRIS

The mast cells located in the intestinal mucosa of a non-eutherian mam mal were studied in comparison with those in the skin of the ear. In t he intestinal mucosa, the mast cells exhibited a more variable shape, larger cytoplasmic granules and greater sensitivity to fixatives regar ding their staining towards Toluidine Blue. Ultrastructurally, these g ranules were more heterogeneous but lacked the crystalline content fou nd in granules of skin mast cells; lipid body-like organelles were fou nd only in the mucosa-located mast cells. Histochemically, they differ ed from skin mast cells by the absence of periodic acid-Schiff (PAS)-p ositive granules. Unlike the mucosal mast cells of the rat, they fluor esced brilliant yellow after berberine treatment, which is evidence of the presence of heparin.