The mechanism of histamine release induced by the ionophore X537A from isolated rat mast cells. I. Significance of monovalent cations, calcium, metabolic energy and temperature

Role of 5-HT3 receptors and afferent fibers in the effects of mast cell degranulation on colonic motility in rats

BACKGROUND/AIMS

Mediators released by mast cell degranulation contribute to digestive motility disturbances. According to the role of serotonin and the close proximity of mast cells to nerves, the aim of this study was to assess the role of 5-hydroxytryptamine 3 (5-HT3) receptors, capsaicin-sensitive afferent fibers, and some of their neuropeptides (substance P and calcitonin gene-related peptide) in colonic motor alterations induced by degranulation of mast cells by the compound BrX-537A.

METHODS

The effects of BrX-537A (2 mg/kg intraperitoneally) were determined by electromyography in conscious rats implanted with electrodes in the cecocolonic wall.

RESULTS

BrX-537A inhibited cecocolonic myoelectric activity for 7-8 hours. A primary and dramatic reduction of spike burst frequency, lasting 30 minutes, was affected by none of the pretreatments tested. The following inhibition was fully antagonized by ketotifen (mast cell stabilizer), granisetron and ondansetron (5-HT3 antagonists), RP-67,580 (NK1 antagonist), and perivagal capsaicin pretreatment. A temporary blockade was observed after administration of CP-96,345 (NK1 antagonist) and in rats systemically treated by capsaicin. The calcitonin gene-related peptide antagonist hCGRP(8-37) did not modify the BrX-537A-induced inhibition.

CONCLUSIONS

5-HT3 receptors, sensory afferent fibers reaching the vagus nerves, and substance P are major components of the colonic motor inhibition induced by mast cell degranulation.

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.

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.

Characteristics of histamine release evoked by acetylcholine in isolated rat mast cells

1. Histamine secretion from rat mast cells occurs in the presence of nanomolar concentrations of acetylcholine. 2. Intact glycolytic and oxidative metabolism is required for the acetylcholine-induced histamine secretion. Removal of extracellular glucose, hypoxia, cyanide and monoiodoacetate almost completely inhibit the secretion. 3. The secretion of histamine is dependent on the extracellular H ion concentration and is blocked when the cells are exposed to Na-deficient media. 4. The order of potency of cholinrgic agonists in evoking the secretion of histamine is oxotremorine > acetylcholine > choline > carbamycholine > nicotine. 5. Atropine competitively blocks the acetylcholine-induced histamine secretion, indicating the presence of cholinergic muscarinic receptors on mast cells. 6. Dibutyryl cyclic AMP and adrenaline inhibit the acetylcholine-induced histamine secretion, indicating a regulatory function afforded by cyclic nucleotides in the cholinergic histamine release.

A protective action of disodium cromoglycate against the contraction of guinea-pig ileum induced by various pharmacological stimulants

The effect of disodium cromoglycate (DSCG) on the contraction of isolated guinea-pig ileum induced by histamine, acetylcholine and serotonin has been investigated. DSCG protected ileum against all agents tested. The action of DSCG at concentrations of 10(-3) to 10(-2) M was both dose- and time-dependent. Furthermore, DSCG inhibited compound 48/80-induced histamine release from isolated mast cells over the same range of concentrations. The anti-histaminic action of DSCG was reversible and after 2 h the ileum responded normally to histamine. DSCG-induced inhibition of the contractile response to histamine could be overcome by increasing concentrations of histamine but not by extracellular calcium. A mechanism of the action of DSCG, either against the contraction of ileal smooth muscle or against histamine release from mast cells, is discussed with a view to the inhibition of the utilization of calcium ions by both cells.

Failure of acetylcholine to release histamine from rat mast cells

The action of various salts of acetylcholine on isolated mast cells from Wistar and F1 hybrids of Wistar and August rats was investigated. None of the acetylcholine salts within the concentration range 10(-12) M to 10(-2) M was able to release histamine either from Wistar or from hybrid mast cells. Compound 48/80, used as a control, was active in both cases. The results obtained are in opposition to some recent reports. The possible reasons for these contradictions are discussed.

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.