The dynamics of mast cell secretion studied by vital berberine staining

The fluorescent cationic dye berberine in combination with histamine release studies have been used to explore the different steps of the mast cell secretory process. We have previously shown that quantitation of heparin release by the binding of berberine to fixed mast cells can be used as a direct measure of release of granules. This report summarizes recent work using berberine as a vital stain demonstrating the secretory activity of mast cells. After membrane stabilization with polyethylene glycol (PEG) normal mast cells exclude the dye while mast cells stimulated to secretion with polymyxin B show a strongly fluorescent dye binding to individual cytoplasmic granules. The mean fluorescence intensity of the cell populations after vital berberine staining was compared both to heparin and histamine release. The results strongly suggest that berberine, under the vital staining conditions used, is a marker of intracellular granules that have released histamine. The vital staining method was also used to study membrane events following a polymyxin B-induced secretion. The mean fluorescence intensity decreased by 75% during the first hour after the termination of a polymyxin B stimulation while the mast cell content of histamine and heparin remained constant. The findings support the idea that the membranes are rapidly restored after mast cell secretion, permitting a selective amine release without accompanying release of heparin or other matrix components of the granules.