Receptor-mediated calcium entry is required for maximal effects of platelet activating factor primed responses in human neutrophils.

The effect of receptor mediated calcium entry (RMCE) on platelet activating factor (PAF) stimulated human neutrophils (PMNs) was investigated using SKF 96365, a selective inhibitor of RMCE. Changes in cytosolic calcium concentration were determined by the fluorometric dye indo-1, AM, superoxide generation by cytochrome c reduction, and CD11b surface expression by flow cytometry. SKF 96365 pre-treatment diminished the cytosolic calcium rise in PAF primed PMNs. SKF 96365 treatment significantly (p < 0.05) decreased superoxide generation in PAF primed PMNs, but did not affect activation of the PMN oxidase by fMLP or PMA. Chelation of extracellular calcium by EGTA, intracellular calcium by BAPTA, AM, and RMCE blockade by SKF 96365 all statistically inhibited the PAF induced increase in surface expression of CD11b (p < 0.05); moreover, SKF 96365 inhibited to a greater extent than EGTA or BAPTA, AM treatment. These results suggest that RMCE is required for maximal effects of PAF on PMN function.