Chemoattractant-induced respiratory burst: increases in cytosolic Ca2+ concentrations are essential and synergize with a kinetically distinct second signal.
The role of the cytosolic free Ca2+ concentration ([Ca2+]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 Ca2+-ATPase of intracellular stores, as a tool to selectively manipulate Ca2+ release from intracellular stores and Ca2+ influx across the plasma membrane. We thereby temporarily separated the Ca2+ 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 [Ca2+]c elevation. fMLP was unable to activate the respiratory burst without [Ca2+]c elevation. Thapsigargin-induced Ca2+ 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 [Ca2+]c elevation. The second signal was long lasting (>15 min) provided that there was no rise in [Ca2+]c and that the receptor was continuously occupied. The second signal was inactivated by high [Ca2+]c elevation. Our results demonstrate that [Ca2+]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 Ca2+-independent signal that activates the respiratory burst in synergy with [Ca2+]c.
Foyouzi-Youssefi
R
R
Division of Infectious Diseases, University Hospital, 1211 Geneva 14, Switzerland.
Petersson
F
F
Lew
D P
DP
Krause
K H
KH
Nüsse
O
O
D002118:Calcium / Q000378:metabolism*; D002630:Chemotactic Factors / Q000494:pharmacology*; D018922:HL-60 Cells; D006801:Humans; D016897:Respiratory Burst / Q000187:drug effects*; D015290:Second Messenger Systems; D015398:Signal Transduction
D002630:Chemotactic Factors; D002118:Calcium