IFN-GAMMA INDUCES CALCIUM TRANSIENTS AND INCREASES THE CAPACITATIVE CALCIUM-ENTRY IN HUMAN NEUTROPHILS

We have previously reported that long-term priming of human polymorpho nuclear neutrophilic granulocytes (PMN) with interferon-gamma (IFN-gam ma) increased the fMLP-stimulated calcium influx, We now show that als o after short-term incubation with IFN-gamma, PMN calcium metabolism i s modulated, Single adherent cells in three different calcium-containi ng buffers (high, normal, and low [Ca2+]) were stimulated with the bac terial peptide fMLP or the Ca-ATPase inhibitor thapsigargin (Tg) after about 5 min preincubation with IFN-gamma, The results of this protoco l indicated that IFN-gamma increases both calcium influx and calcium s equestration, Store dependent Ca2+ influx, directly measured on readdi tion of calcium to Tg-treated cells incubated in EGTA buffer, was sign ificantly enhanced in IFN-gamma-treated cells, This effect of IFN-gamm a was enhanced by the tyrosine kinase inhibitor herbimycin A, Striking ly, in low extracellular calcium concentrations, IFN-gamma induced cal cium transients in 20%-60% of the cells, The proportion of PMN respond ing with Ca2+ transients increased with decreasing extracellular calci um concentration, Average lagtime from addition of IFN-gamma to a resp onse that could be measured was 7.3 sec, and average increase in [Ca2] above the basal level was 790 nM, These IFN-gamma-induced transients could not be depressed by herbimycin A, Thus, IFN-gamma can increase capacitative calcium influx, induce calcium transients, and possibly a ffect calcium sequestration in human PMN.