Quantitative Correlation between Degranulation and Histamine Release Following Exposure of Rat Mast Cells to Compound 48/80 in vitro

The relationship between the release of histamine and 35S‐labelled heparin from mast cells exposed to compound 48/80 in vitro has been studied in order to elucidate the mechanism of histamine release induced. The cells were taken from rats injected 3, 6, 12 or 20 days earlier with Na235SO4. A good correlation was found between the two release curves. From studies of the 35S/protein ratio in the extruded granules and granules obtained by water lysis of the washed compound 48/80‐treated cells it appears that the 35S‐labelled heparin was first evenly distributed with respect to the granule protein 12 to 20 days after injection. Using cells taken after such an interval the ratio percentage histamine release/percentage 35S release was found to be 1.1–1.4. We conclude from these results and from the similarity between the time courses of histamine and 35S release that the mechanism of histamine release induced by compound 48/80 involves an initial extrusion of histamine‐cotnaining granules, followed by an exchange of histamine in the extruded granules and cations in the extracellular medium.