Activation of Human Neutrophils with Chemotactic Peptide, Opsonized Zymosan and the Calcium Ionophore A23187, But Not with a Phorbol Ester, is Accompanied by Efflux and Store-Operated Influx of Calcium

The objective of this study was to monitor alterations in cellular Ca²⁺ metabolism following activation of neutrophils with receptor(chemotactic peptide, FMLP, 1 M; opsonized zymosan, OZ, 0.5 mg/ml) and non-receptor (calcium ionophore, A23187, 1 M; phorbol 12-myristate 13-acetate, PMA, 25 ng/ml)-mediated stimuli of the pro-inflammatory functions of these cells. Ca²⁺ fluxes in activated neutrophils were measured using a fura-2-based spectrofluorimetric method in combination with radiometric (⁴⁵Ca) procedures which facilitate distinction between net efflux and net influx of the cation. Exposure of neutrophils to receptor-mediated stimuli and to A23187 was associated with an abrupt increase in cytosolic Ca²⁺ coincident with a rapid efflux of the cation which terminated at around 30 s. In the case of FMLP and OZ, this was followed by a delayed (30–60 s), store-operated influx of Ca²⁺, which was complete at around 5 min after addition of the stimulus. With A23187, however, influx of Ca²⁺ occurred immediately following activation of the cells. There were no detectable alterations in cytosolic Ca²⁺ or measurable net efflux or influx of the cation above control levels in PMA-activated neutrophils. These data demonstrate that FMLP, OZand A23187-mediated alterations in neutrophil cytosolic Ca²⁺ are due to mobilization of both intracellular and extracellular cation, while activation of neutrophils by PMA is independent of alterations in cytosolic Ca²⁺.