In situ characterization of mast cells in the frog Rana esculenta

The number, distribution, and ultrastructural characteristics of mast cells were assessed in the tongue, heart, and kidney of the frog Rana esculenta. The density of tongue mast cells (253+/-45 mast cells/mm(2)) was significantly higher than that of the heart (5.3+/-0.4/mm(2)) and kidney (15.3+/-1.4/mm(2)). A striking feature of this study was the remarkable association of frog mast cells to nerves. The ultrastructural study of the mast cell/nerve association demonstrated that mast cells were closely apposed to or even embedded in nerves. Mast cells were also physically associated with melanocytes even in the heart. Mast cells were Alcian blue(+)/safranin(+) in the tongue and in the peritoneum, whereas in the heart and in the kidney they were Alcian blue(-)/safranin(+). The mast cells in the lamina propria of the gastrointestinal tract were Alcian blue(+)/safranin(-). The cytoplasm of frog mast cells was packed with numerous heterogeneous, membrane-bound granules. The ultrastructure of these cytoplasmic granules was unique, being totally unlike any other previously described granules in other animal species as well as in man. The histamine content/frog mast cell (approximate to 0.1 pg/cell) was approximately 30 times lower than that of human mast cells isolated from different tissues (approximate to 3 pg/cell). A monoclonal anti-histamine antibody was used to confirm the ultrastructural localization of histamine in secretory granules in frog mast cells.