Early stages of anaphylactic reaction in rat mast cells revealed with freeze-fracturing.

The aim of this study was to find the early exocytotic signs in passively sensitized rat mast cells stimulated with antigen using freeze-fracturing technique and to establish if histamine release precedes or follows exocytosis. It has been shown that histamine release was detectable as early as 5 sec, and completed in approx. 20-30 sec, after challenge with antigen. However, the earliest membrane changes were observed after 20 sec exposure to the releaser. They were manifested with fusion between granule membranes and etchable pores in the plasma membrane. Areas exhibiting depletion or aggregation of intramembrane particles have not been seen. It can be concluded, that during anaphylactic reactions histamine secretion precedes the process of granule exocytosis.