The increase in intracellular free calcium associated with IgG gamma 2b/gamma 1 Fc receptor-ligand interactions: role in phagocytosis.

The concentration of cytosolic free calcium, Ca2+i, was measured in J774 mouse macrophages by use of the fluorescent indicator quin-2. Resting Ca2+i was 87 nM. Addition of a number of specific ligands to the immunoglobulin gamma 2b/gamma 1 Fc receptor resulted in a transient increase in Ca2+i, the magnitude of which depended on the extent of receptor aggregation. Monovalent ligands gave only a small Ca2+ signal but blocked cell response to subsequent addition of multivalent ligands. Incubation with antibody-coated erythrocytes raised macrophage Ca2+i to micromolar levels. Ca2+i changes were only partially inhibited by the absence of external Ca2+, suggesting the release of Ca2+ from internal stores in addition to an influx of external Ca2+. These internal stores were not limited to mitochondria. An optimal range of Ca2+i was required for phagocytosis. Buffering Ca2+i with quin-2 and treating cells with quinine in the absence of external Ca2+ resulted in inhibition of phagocytosis. Increasing Ca2+i to micromolar levels with the calcium ionophore A23187 also resulted in similar inhibitory effects. We suggest the involvement of localized cytosolic Ca2+ gradients in generating the signals necessary for phagocytosis.