Role of membrane bound calcium in histamine secretion from rat peritoneal mast cells

Calcium loosely bound to the mast cell membrane may be utilized for histamine release induced by antigen, concanavalin A, compound 48/80 and the calcium ionophore A23187. Cells incubated in the presence of calcium and diluted into a medium free of divalent cations give a maximal release of histamine which decays with time, consistent with dissociation of the ion from the membrane. Anti-rat IgE and suboptimal concentrations of the ionophore show an immediate decrease in response followed by a further progressive decay. These results are consistent with the slower time-course of secretion shown by these agonists, thus permitting dissociation of calcium from the membrane before exocytosis is induced. In accord with this hypothesis, the initial supression of response to the ionophore is reversed by preincubation of the cells with adenosine which enhances the rate of histamine release. The response to dextran is totally abolished by the described treatment, supporting suggestions that free, extracellular calcium may be required for the polysaccharide to express its activity.