Immunoglobulin E receptor cross-linking induces oscillations in intracellular free ionized calcium in individual tumor mast cells

Fura-2 fluorescence in single rat basophilic leukemia cells was monitored to study the rise in intracellular free ionized calcium (Ca2+]i) produced by aggregation of immunoglobulin E receptors. Repetitive transient increases in Ca2+]i were induced by antigen stimulation and were measured using digital video imaging microscopy at high time resolution. The Ca2+]i oscillations were not dependent upon changes in the membrane potential of the cells and were observed in cells stimulated with antigen either with or without extracellular Ca2+. Transient oscillations in Ca2+]i were also observed when calcium influx was blocked with La3+. These results suggested that during antigen stimulation of cells under normal physiological conditions, release of Ca2+ from intracellular stores makes an important contribution to the initial increase in Ca2+]i. Oscillations in Ca2+]i are not induced by elevating Ca2+]i with the calcium ionophore ionomycin. Mitochondrial calcium buffering is not required for Ca2+]i oscillations to occur. The results show that rat basophilic leukemia cells have significant stores of calcium and that release of calcium from these stores can participate in both the initial rise and the oscillations in Ca2+]i.