[Mode of action of protamine sulfate on histamine secretion in the rat mast cells].

Protamine sulfate, known for a long time as a histamine releaser, was labeled with a fluorescent dye (FITC). This conjugate was shown to stain selectively the mast cell fraction of rat peritoneal cells. Within a few seconds, the protamine was found inside the cells. Although the cells had lost their histamine completely, no granules were found outside the cells. In the electron microscope, the protamine treated mast cells showed a loss of the electron density of their granules, a vacuolization, and other signs of histamine release. Evidence for a direct connection between the vacuoles and the extracellular fluid was gained by incubating mast cells in FITC-labeled human serum albumin followed by the addition of unlabeled protamine. After washing, the fluorescence was found to be located inside the cells, demonstrating an influx of the FITC-HSA under the influence of protamine. The protamine-induced release reaction is increased after addition of Ca2+, reduced by lowering the temperature, addition of 2-deoxyglucose, or cytochalasin B. Disodium cromoglycate also diminished the histamine release in a dose dependent manner. Protamine did not induce a loss of lactate dehydrogenase from the mast cells. The release reaction is mediated by the cell membrane, as shown by the releasing activity of insolubilized protamine. We conclude that the protamine-induced release is a non-cytotoxic reaction, fulfilling some criteria of the anaphylactic histamine release.