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The Calcium Ionophore Ionomycin can Prime, but not Activate, the Reactive Oxygen Generating System in Differentiated HL‐60 Cells
Author(s) -
Dahlgren Claes
Publication year - 1989
Publication title -
journal of leukocyte biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.819
H-Index - 191
eISSN - 1938-3673
pISSN - 0741-5400
DOI - 10.1002/jlb.46.1.15
Subject(s) - ionomycin , n formylmethionine leucyl phenylalanine , reactive oxygen species , biochemistry , microbiology and biotechnology , calcium , receptor , biology , chemotaxis , stimulation , chemistry , biophysics , endocrinology , organic chemistry
Both the chemotactic peptide formylmethionyl‐leucyl‐phenylalanine (FMLP) and the calcium lonophore ionomycin induced a metabolic response in normal neutrophils. However, the presence of azide, a potent inhibitor of the hydrogen peroxide‐consuming enzymes catalase and myeloperoxidase, was required to detect any release of hydrogen peroxide induced by ionomycin. In differentiated HL‐60 cells, only FMLP stimulation was associated with any notable metabolic activation. The response to FMLP proceeds with a rate and time course similar to that seen in normal cells. The use of ionomycin as a stimulating agent did not result in any detectable activation of the system that generates reactive oxygen metabolites, even if azide was present in the measuring system. Raising the concentration of cytoplasmic free Ca 2+ is therefore not sufficient to activate the system responsible for the generation of reactive oxygen metabolites in HL‐60 cells. However, preincubation with ionomycin primed HL‐60 cells to an increased response during stimulation with the chemotactic peptide FMLP and the phorbol ester PMA. Since HL‐60 cells lack specific granules but have an intact ligand‐receptor coupling mechanism, a role for the subcellular granule is proposed, in the generation of reactive oxygen species in normal granulocytes, and analysis of the data presented leads to two conclusions: 1) FMLP, which acts through cells surface receptors, causes the cells to produce oxygen radicals, which to a large extent are released from the cells, a process that is not dependent on the specific granule content of the cells, whereas 2) ionomycin, which bypasses cell‐surface receptors, is also capable of stimulating an oxygen‐radical formation that is granule dependent and retained inside the cells. Furthermore, the results suggest that an increase in intracellular Ca 2+ is not sufficient to initiate activation of the plasma membrane–bound system that generates reactive oxygen metabolites, but the results support a role for Ca 2+ in the priming event.