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[The mast cell].

A review is presented of the most important morphological and functional characteristics of the mast cell. The cell is ovoid and contains heparin-containing granules in the cytoplasm. These stain metachromatically. In addition to heparin, the granules contain histamine and other inflammatory mediators. The cell is localized perivascularly in the loose connective tissue. The mast cell secretes histamine by exocytosis when it is stimulated immunologically by binding of a specific antigen to IgE molecules in the cell membrane. Histamine secretion may also be induced by non-immunological stimulators such as polymeric amines, neuropeptides and calcium-ionophores. Calcium plays an important role in the secretory process. Immunological secretion of histamine requires the presence of extracellular calcium whereas secretion induced by polymeric amines and neuropeptides can utilize the intracellular calcium depots. Phosphatide inositides released from phospholipides in connection with cell activation release calcium from the intracellular depots and probably play a part in histamine secretion. In addition, the protein phosphorylization reactions catalized by proteinkinase C, probably contribute in the process of secretion. Finally, secretion of histamine depends upon the ATP content of the cell.