Inhibition by cromoglycate of histamine release from rat peritoneal mast cells induced by mixtures of dextran, phosphatidyl serine and calcium ions.

1 Dextran releases histamine from rat peritoneal mast cells in the presence but not in the absence of phosphatidyl serine (PS). With PS (10 mug/ml) present the effect of dextran was concentration-dependent in the range of 0.2-6 mg/ml.2 PS releases little histamine on its own but mixed with dextran (6 mg/ml) produces a graded effect in the range of 0.3-10 mug/ml.3 The combination of dextran and PS releases no histamine in a medium containing less than 0.1 mM calcium. As the calcium concentration is increased, release occurs and a maximum is reached at calcium 1 mM; at higher concentrations release falls off sharply.4 Histamine release by the combination of dextran (6 mg/ml), PS (10 mug/ml) and calcium (1.8 mM) is inhibited by cromoglycate in the same range (1-30 muM) that inhibits anaphylactic histamine release from rat peritoneal cells.5 Inhibition by cromoglycate occurred with all dextran concentrations tested (0.2-15 mg/ml) but high concentrations of PS (30 and 100 mug/ml) overcame the effect of cromoglycate (2 and 10 muM). Calcium concentrations above 1 mM augmented inhibition by cromoglycate 2 and 10 muM.