Calcium release associated with discharge of specific granule contents from human neutrophils

Neutrophil discharge of calcium into the ambient medium was measured, using an ion-sensitive electrode, after cells were stimulated with phorbol myristate acetate. Dose-dependent calcium efflux was observed over the same range of stimulus concentrations associated with specific granule marker release. Calcium efflux was preserved when cells were treated with vanadate to inhibit the plasma membrane calcium ATPase. However, less calcium was released than in previous studies employing a complete secretagogue to discharge both specific and azurophil granule contents. These studies suggest that calcium is stored in both the azurophil and the specific granules of the neutrophil, and can be mobilized from both sites during degranulation.