N-acetyl-L-cysteine and cysteine increase intracellular calcium concentration in human neutrophils

N-acetyl-L-cysteine (NAC) and cysteine have been implicated in a number of human neutrophils' functional responses. However, though Ca(2+) signaling is one of the key signalings contributing to the functional responses of human neutrophils, effects of NAC and cysteine on intracellular calcium concentration ([Ca(2+)](i)) in human neutrophils have not been investigated yet. Thus, this study was carried out with an objective to investigate the effects of NAC and cysteine on [Ca(2+)](i) in human neutrophils. We observed that NAC (1 µM ~ 1 mM) and cysteine (10 µM ~ 1 mM) increased [Ca(2+)](i) in human neutrophils in a concentration-dependent manner. In NAC pre-supplmented buffer, an additive effect on N-formyl-methionine-leucine-phenylalanine (fMLP)-induced increase in [Ca(2+)](i) in human neutrophils was observed. In Ca(2+)-free buffer, NAC- and cysteine-induced [Ca(2+)](i) increase in human neutrophils completely disappeared, suggesting that NAC- and cysteine-mediated increase in [Ca(2+)](i) in human neutrophils occur through Ca(2+) influx. NAC- and cysteine-induced [Ca(2+)](i) increase was effectively inhibited by calcium channel inhibitors SKF96365 (10 µM) and ruthenium red (20 µM). In Na(+)-free HEPES, both NAC and cysteine induced a marked increase in [Ca(2+)](i) in human neutrophils, arguing against the possibility that Na(+)-dependent intracellular uptake of NAC and cysteine is necessary for their [Ca(2+)](i) increasing activity. Our results show that NAC and cysteine induce [Ca(2+)](i) increase through Ca(2+) influx in human neutrophils via SKF96365- and ruthenium red-dependent way.