Morphology and Storage Properties of Rat Mast Cell Granules Isolated by Different Methods

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Abstract
Pure granule fractions were obtained from rat mast cells by sonication in sucrose for different times and at different amplitudes. Two types of mast cell granule were found. One type appeared dark blue in the light microscope when stained with toluidine blue–azur A and was homogeneous, electron dense and surrounded by a trilaminar membrane when observed in the electron microscope; thus this type had the same appearance as mast cell granules in situ. The second type appeared pink after staining with the above dye and had a swollen, reticular appearance with a reduced electron density and no surrounding membrane when observed in the electron microscope. With increasing sonication time and amplitude there was an increase in the proportion of the swollen, less electron dense granules with no surrounding membrane and a concomitant decrease in the amount of histamine retained (as shown by the histamine/ heparin and histamine/protein ratios) after washing in isotonic sodium chloride. Granules isolated from water‐lysed mast cells or mast cells treated with compound 48/80 were all of the second type with no perigranular membrane: they released their histamine when suspended in isotonic sodium chloride solution.