Mechanism of histamine release induced by the ionophore X537A from isolated rat mast cells

Characteristics of histamine release from rat mast cells induced by a bracken toxin, braxin A1

The effect of braxin A1, a new bracken glucoside, on histamine release from isolated rat peritoneal mast cells was studied. Braxin A1 caused the release of histamine in a dose-dependent manner; the release was slow and increased gradually with time, finally reaching a maximum release of 100%. The action of braxin A1 depended on the incubation temperature in the range from 4 degrees C to 49 degrees C, while it was almost abolished at 0 degree C. The action of braxin A1 was unaffected by removing calcium or any inorganic ions from the incubation medium and by the addition of 2,4-dinitrophenol or theophylline. The mast cells exposed to braxin A1 were vitally stained with trypan blue and swelled greatly. The cell swelling was characterized by the protrusion of swollen cytoplasmic granules. The present results for braxin A1 were similar to those for the ionophore X537A except for the extracellular inorganic ion dependency, but they were different from those observed with compound 48/80. These results suggest that braxin A1 releases histamine from mast cells without both exocytosis and membrane lysis, but with a cytotoxic action on cytoplasmic membranes by a different mode of action from that of X537A.

Histamine releasing action of calcium ionophore 985-I

The polyether antibiotic 985-I induced histamine release from rat and mouse mast cells and human basophils. Histamine release induced by low concentrations (10-50 microM) of the ionophore was a selective (noncytotoxic) process. It was energy and Ca2+-dependent and was potentiated by glucose. In this respect the mode of action of 985-I was similar to that of the Ca2+-ionophore A23187. On the other hand some pharmacological agents (phencarol, verapamil and amitriptyline) inhibited histamine secretion induced by 985-I but not A23187-induced histamine release. These data point to some differences between the mechanisms of action of 985-I and A23187.

Valinomycin, a degranulating agent in rat mast cells which inhibits calcium-uptake

The effect of valinomycin on both, mast cell histamine release and on calcium (45Ca)-uptake processes was examined. Pleural and peritoneal mast cells were purified in isotonic Percoll (pH = 7) and mixed populations were used in the experiments. Valinomycin (10(-9)-10(-5) M) stimulated histamine release in isolated rat mast cells when the incubation medium contained high K+ concentrations (Tris-K+ with 150 mM K+), but not in other media such as Tris-Na+ (120 mM Na+) or Tris-sucrose (300 mM sucrose). In contrast, in the absence of valinomycin, elevated K+ levels in the external environment did not activate mast cell secretion. Optimum response in valinomycin-treated mast cells was obtained when the cells were incubated for 60 min. Also valinomycin (10(-5) M) induced substantial inhibition of 45Ca-uptake while lower doses (10(-9)-10(-7) M) did not affect or only slightly increased uptake. In this paper valinomycin is shown to be a degranulating agent eliciting mediator release in mast cells incubated in the presence of high K+ levels, which does not require extracellular calcium and inhibits 45Ca uptake. The possibility that valinomycin acts as a K+ ionophore, as in other secretory systems, is discussed.

The influence of hypertonicity on histamine release from isolated rat mast cells

Increasing the tonicity of the incubation medium gradually inhibited histamine release from isolated rat mast cells when induced A-23187, ATP, Thapsigargin, sodium fluoride and compound 48/80 in the presence of extracellular calcium, as well as by the latter in the presence of calcium. In contrast, hypertonicity had but negligible effect on the release caused by the monovalent cation inophore X-537A. The swelling action induced by both ATP and X-537A on rat mast cells was markedly depressed by hypertonicity. Thus, the swelling action seemed to be inherent to the mechanism by which ATP stimulates mast cells to a calcium-dependent histamine secretion, whereas this was not the case with X-537A. For Thapsigargin and sodium fluoride it was demonstrated that only the secretory step, induced by calcium, was inhibited by hypertonicity, and this could be reversed by adjusting the incubation medium to isotonicity. Therefore, the results suggest that the uptake of calcium in the rat mast cells after stimulation is a passive process.

On the mechanism of histamine release induced by thapsigargin from Thapsia garganica L

Thapsigargin (Tg) is a pure chemical compound isolated from Thapsia garganica with a molecular weight of 650. It releases histamine from isolated rat mast cells but not from isolated histamine-retaining mast cell granules. The rate of release is markedly influenced by pretreatment of mast cells with Tg prior to the addition of calcium. In agreement with the effect of the ionophore A23187 but in contrast to many other calcium-dependent histamine-releasing agents, cells preincubated with Tg respond to the secretory action of calcium whenever the ion is introduced. However, after dilution of Tg-pretreated cells histamine release induced by the addition of calcium became dependent on the time of its addition. The secretory reaction induced by Tg and calcium can be divided into a two-step reaction at 37 degrees C. Pretreatment of mass cells with Tg renders the cells insensitive to the secretory action of compound 48/80 in the absence of calcium, and this effect could be partly counteracted if 1 mM of strontium was added together with compound 48/80. It is concluded that among various calcium- and energy-dependent histamine-releasing agents Tg most closely resembles the action of fluoride on isolated rat mast cells.

The mechanism of histamine release induced by the ionophore X537A from isolated rat mast cells. II. The relationship between increase of cell volume and histamine release

The ionophore X537A induced swelling of isolated rat mast cells parallel to histamine release. Both actions were depressed by extracellular calcium and BSA, temperatures below 37 degrees C, NEM, PMSF, and TTX, and were enhanced by high potassium and pretreatment of the cells with ATP. DSCG, theophylline, and DFP enhanced the histamine release noted after 10 min of incubation without influencing the swelling action of X537A. The swelling action could not be separated from histamine release and it is suggested that it might be inherent in the mechanism of secretion induced by X537A. The present results further distinguish histamine release induced by the two ionophores X537A and A23187.