Release of 0 sub(2) super(-) by human umbilical cord blood-derived eosinophils: role of intra- and extracellular calcium

The aim of our study was to investigate the physiologic mechanisms involved in eosinophil activation as an essential prerequisite to disrupting the biochemical cascade that triggers inflammation, thereby attenuating the effect of this activation or, ideally, preventing it from occurring. We have, therefore, examined the nature of the fMLP- and PAF-induced [Ca2+]i, rise and the relationship between the [Ca2+]i rise and 0 sub(2) super(-) production in human umbilical cord blood-derived eosinophils cultured in the presence of IL-3 and IL-5. These cells responded to fMLP or PAF (1 mu M each) with an increase in [Ca 2+]i (217.3 plus or minus 22.1 and 197.8 plus or minus 22.1 nM respectively) which was associated with production of 0 sub(2) super(-) (40.2 plus or minus 8.2 and 35.2 plus or minus 7.6 pmol/min/106 cells respectively). The role of Ca2+ in the induced respiratory burst was studied by changing the availability of Ca2+ in the intra- and extracellular compartments. Removal or chelation of extracellular Ca2+ induced a reduction of both the fMLP and PAF-induced [Ca 2+]i rise and 0 sub(2) super(-) production. Chelation of intracellular Ca2+ induced a concentration-dependent inhibition of fMLP- and PAF-induced [Ca2+]i rise and caused a decrease in 0 sub(2) super(-) production. SK&F 96365 had a stimulatory effect on PAF-induced [Ca2+]i rise and on fMLP-induced 0 sub(2) super(-) production, this phenomenon was not observed with extracellular Ca2+ removal or chelation. Furthermore, Ni2+ exhibited an inhibition of both fMLP and PAF-induced [Ca2+]i rise and 0 sub(2) super(-) production. Finally, both fMLP and PAF induced an increase in divalent cation influx that was further augmented by thapsigargin. Our results indicate that fMLP and PAF dependent 0 sub(2) super(-) production in human eosinophils require intra- and extracellular Ca2+ and that Ca2+ influx is necessary for optimal activation.