Interaction between barium, strontium and calcium in histamine release by compound 48/80

Pre-incubating rat peritoneal and pleural mast cells for 30 min at 2 degrees C in Ca2+-free Tyrode containing Ba2+ (30 mM) markedly reduced histamine release by compound 48/80 (0.5 microgram/ml). Evoked secretion was not significantly altered by pre-incubation with Sr2+ (30 mM) at this temperature whilst Mg2+ (30 mM) and La3+ (0.1 mM) slightly inhibited and potentiated release respectively. The effect of Ba2+ was concentration related and progressively reversed by Ca2+ (1--10 mM). Pre-incubation at 37 degrees C in Ca2+-free medium alone substantially reduced histamine release by compound 48/80. This reduction was unaltered by either Mg2+ (30 mM) or La3+ (0.1 mM), prevented by either Sr2+ (30 mM) or Ca2+ (1 mM) and augmented by Ba2+ (30 mM) which also markedly increased spontaneous histamine release during pre-incubation at 37 degrees C. Results suggest that Ba2+ and Sr2+ interact with cell-fixed calcium to modulate histamine release by compound 48/80.