IMMUNOCYTOCHEMICAL LOCALIZATION OF HISTAMINE IN SECRETORY GRANULES OF RAT PERITONEAL MAST-CELLS WITH CONVENTIONAL OR RAPID MICROWAVE FIXATION AND AN ULTRASTRUCTURAL POSTEMBEDDING IMMUNOGOLD TECHNIQUE

We used a post-embedding immunogold labeling approach to define the fine-structural localization of histamine in rat peritoneal mast cells that were fixed using either standard aldehyde fixation or a fast microwave-aldehyde fixation method. Specimens were processed routinely for electron microscopy. Thin sections were exposed first to guinea pig antihistamine antiserum and then to gold-conjugated goat IgG directed against guinea pig IgG. By transmission electron microscopy, gold particles were localized to the matrix of cytoplasmic granules. Control sections treated with non-immune sera did not show labeling of mast cells. Adsorption of antihistamine antiserum with purified histamine or histamine bound to agarose showed a significant reduction (p<0.005) in granule staining. We also confirmed that our isolation procedures yielded functionally competent mast cells which released histamine when stimulated with sheep anti-rat IgE antiserum or with compound 48/80. These studies define the conditions of fixation for electron microscopy that are appropriate for the localization of histamine in the granule matrix of rat peritoneal mast cells.