Effect of low temperature on mast cell exocytosis. Early cytoplasmic vesicle formation and the role of cytoskeleton.

Mast cells stimulated with adriamycin at 4 degrees C underwent a unique exocytotic reaction. Rat peritoneal cells including mast cells were stimulated in vitro with adriamycin (100 micrograms/ml) for 0, 10, 30 or 60 sec and observed by transmission electron microscopy. Early changes could be observed after 10 sec stimulation and consisted in an approximately 5-fold increase (p < 0.001) of 0.05-0.2 micron diameter cytoplasmic vesicles. The Golgi apparatus showed signs of activation and vacuolization. From 10 to 30 sec, cytoplasmic vesicles fused with the perigranular membranes and with the membranes of developing secretory channels. At 60 sec, the number of vesicles and vacuoles diminished to nearly two-fold starting levels. The exocytotic reaction characteristically resulted in the formation of enormously dilated granular cavities. The secretory process appeared incomplete; after 60 sec, in fact, maximal histamine release was 20% and exocytosis could be found in approximately 30% of mast cells. Pre-incubation with vinblastine followed by adriamycin stimulation at 37 degrees C determined a dose-dependent inhibition of histamine release which was accompanied by the ultrastructural appearance of numerous 0.05-0.5 micron cytoplasmic vesicles and by signs of inhibited exocytosis. Our results support the concept that hyperstability of the cortical cytoskeleton coupled with microtubule perturbation would be responsible for the depressed pattern of mast cell exocytosis observed at 4 degrees C. Although stimulation at 4 degrees C induces a paradoxal secretory process, we believe that this approach may represent a useful model for understanding some basic mechanisms of exocytosis in mast cells.