Histamine secretion was induced by substance P, in a dose-dependent manner, from rat peritoneal mast cells, both in the presence and absence of Ca2+ in the medium, and disodium cromoglycate (DSCG) produced a dose-dependent inhibition of the histamine secretion in Ca2+-containing medium. However, in the absence of Ca2+, DSCG was ineffective or had a far weaker activity. Mg2+, Sr2+ and Ba2+ were ineffective in restoring the DSCG activity when added to medium devoid of divalent metal ions. Therefore, extracellular Ca2+ seems to be a specific requirement for the binding of DSCG to its “receptors” on the mast cell surface or some steps in the DSCG action.
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