Inhibition of histamine secretion from mast cells

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Abstract
Histamine secretion from mast cells may be inhibited by elevated intracellular levels of cAMP and by several anti-allergic drugs. These compounds are claimed to act directly on the Ca-gating mechanism activated by the anaphylactic reaction, preventing influx of Ca2+ from the external environment and so blocking exocytosis. To examine this hypothesis, the histamine secretion induced in rat peritoneal mast cells by IgE-directed ligands (in the presence and absence of added Ca) and by the ionophore A23187 was compared. Exocytosis evoked by these former agents was originally considered to be almost totally dependent on extracellular Ca but recent studies have shown otherwise. In the absence of added cation, the agents act by mobilizing membrane-bound or intracellular stores of Ca. A variety of anti-allergic drugs are potent inhibitors in the conditions used, suggesting that alternative explanations for their action must be sought. [Drugs used in this study include cromoglycate, theophylline, 8-bromocyclic AMP and quercetin].