A quantitative spectrophotometric study of the mast cell

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1. 1. Mast cells of rat peritoneal fluid, stained in smears with toluidine blue, are favorable objects for spectrophotometric analysis. Characteristic marked heterogeneity of their cytoplasm presents no outstanding problem when scanning procedures are used. 2. 2. Technical aspects of metachromatic staining were investigated. A metachromatic ratio and total extinctions were used to assess the effects of fixation, alcohol, water and pH on the dye reaction in mast cells. A short staining method for the mast cells is outlined. 3. 3. Based on measurements in 1250 cells, some quantitative aspects of stained mast cell populations and individuals are described. Metachromasy in many cells attains levels characteristic of extremely concentrated solutions of toluidine blue, of maximally metachromatic solutions of the dye with sulfated mucopolysaccharides, or of selected areas in cartilage matrix. Calculated amounts of dye bound per cell are on the order of 3 × 10 −14 mole or less, the average dye concentration being 0.06 M or 1.8 per cent. Mere inspection shows that the dye must be in compartments (the granules) at much higher and variable concentrations. 4. 4. Synthesis of the metachromatic component(s) of the mast cell has superficial characteristics of a massive secretory process. 5. 5. Cortisone and thyrotropic hormone, in a few preliminary experiments, produced marked changes in the mast cells. In addition to distinctive morphological changes, the proliferation of a relatively non-metachromatic component seems to take place in otherwise normal-looking mast cells, followed later by granular changes and cellular polymorphism. 6. 6. The use of a sum of extinctions at two wavelengths (546 mμ and 630 mμ for toluidine blue) to measure the total amount of metachromatic dye bound in the mast cells is discussed. Internal evidence justifies the procedure. Independent tests are still required.