Flow cytometry reveals different lag times in rapid cytoplasmic calcium elevations in human neutrophils in response to N-formyl peptide

Flow cytometric anlyses were performed to study intracellular single-cell calcium transients (Ca2+)i in suspended human neutrophils during the initial phase of N-formyl peptide stimulation. Thereby, two neutrophil populations becam apparent. Early maximally Ca(2+)-responding (high fluorescence) neutrophils and not yet Ca(2+)-responding (low fluorescence) neutropils, but no neutrophils with intermediate levels of (Ca2+)i were detected. Within 7 s the number of low fluorescence neutrophils decreased and the number of high fluorescence neutrophils increased maximally. This suggests that (Ca2+)i transients occured abruptly in individual neutrophils within a time interval below 1 s. At lower N-formyl peptide concentrations the lag times of individual neutrophils and the inverval time of maximal activation of the (Ca2+)i responding neutrophil population increased, however the percentage of (Ca2+)i responding cells decreased.