Capacitative Ca2+ influx and activation of the neutrophil respiratory burst. Different regulation of plasma membrane- and granule-localized NADPH-oxidase.
The neutrophil NADPH-oxidase may be activated in the plasma membrane, resulting in release of oxygen metabolites extracellularly, or in the granule or phagosomal membranes, giving intracellular production of oxidants. An increase in [Ca2+]i mediated through binding of fMLF to its receptor is part of a signaling cascade that activates the plasma membrane-localized oxidase. In contrast, a rise in [Ca2+]i induced by a Ca2+ ionophore results in activation of the intracellular pool of oxidase. We mimicked fMLF-induced emptying of intracellular Ca2+ stores with thapsigargin. This induced a pronounced intracellular oxidase activity but no extracellular release of oxidants. The thapsigargin-induced effect was dependent on capacitative Ca2+ influx, because the effect was inhibited dose-dependently by EGTA and the Ca2+ channel blocker La3+. At La3+ concentrations between 200 and 400 microM, thapsigargin also induced a massive extracellular production of superoxide anion. No other channel blockers tested induced a similar effect. We conclude that elevation in [Ca2+]i by capacitative Ca2+ influx induces NADPH-oxidase activation at an intracellular site. Further, activation of the plasma membrane-localized NADPH-oxidase is regulated by a more complex Ca2+ signaling, involving capacitative Ca2+ influx and possibly the specific action of La3+-sensitive Ca2+ channels.
Granfeldt
Daniel
D
The Phagocyte Research Laboratory, Department of Rheumatology, University of Göteborg, Sweden.
Samuelsson
Marie
M
Karlsson
Anna
A
D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D002462:Cell Membrane / Q000201:enzymology*; D003594:Cytoplasmic Granules / Q000201:enzymology*; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation; D007811:Lanthanum / Q000494:pharmacology; D019255:NADPH Oxidases / Q000378:metabolism*; D009504:Neutrophils / Q000378:metabolism*; D016897:Respiratory Burst; D015398:Signal Transduction; D019284:Thapsigargin / Q000494:pharmacology
D015220:Calcium Channels; D004533:Egtazic Acid; D019284:Thapsigargin; D007811:Lanthanum; D019255:NADPH Oxidases; D002118:Calcium