Chemoattractant-induced respiratory burst: increases in cytosolic Ca2+ concentrations are essential and synergize with a kinetically distinct second signal
Foyouzi-Youssefi, R.; Petersson, F.; Lew, D.P.; Krause, K.H.; Nüsse, O.
Biochemical Journal 322: 709-718
ISSN/ISBN: 0264-6021 PMID: 9148740 Accession: 008306911
The role of the cytosolic free Ca-2+ concentration ((Ca-2+)-c) and its relationship to other second messengers in the signalling between chemoattractant (e.g. N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP)) receptors and the NADPH oxidase is still poorly understood. In this study, we have used thapsigargin, an inhibitor of the Ca-2+-ATPase of intracellular stores, as a tool to selectively manipulate Call release from intracellular stores and Ca-2+ influx across the plasma membrane. We thereby temporarily separated the Ca-2+ signal from other signals generated by fMLP. and analysed the consequences on the respiratory burst. Under all conditions investigated, the extent of fMLP-induced respiratory burst activation was critically determined by (Ca-2+1)-c elevation. fMLP was unable to activate the respiratory burst without (Ca-2+), elevation. Thapsigargin-induced Ca-2+ influx activated the respiratory burst in the absence of fMLP, but only to approx. 20% of the values observed in the presence of fMLP. The second signal generated by fMLP did not activate the respiratory burst by itself, but acted in synergy with (Ca-2+)-c elevation. The second signal was long lasting ( gt 15 min) provided that there was no rise in (Ca-2+)-c and that the receptor was continuously occupied. The second signal was inactivated by high (Ca-2+)-c elevation. Our results demonstrate that (Ca-2+)-c elevations are an essential step in the signalling between the fMLP receptor and NADPH oxidase. They also provide novel information about the properties of the second Ca-2+-independent signal that activates the respiratory burst in synergy with (Ca-2+)-c.