Biphasic increase in intracellular calcium induced by platelet-activating factor in macrophages.
In single mouse macrophages stimulated by platelet-activating factor (PAF), the intracellular calcium concentration (Cai) monitored with fura-2 at room temperature presents a biphasic increase, including a transient and a more sustained component. After pulse administration of PAF, the first phase lasts for a few seconds and reaches a peak value of 0.5-1 microM Ca2+ at high PAF concentration. The amplitude of this peak is independent of extracellular Ca2+ concentration, suggesting that the initial Ca2+ transient is due to the release of Ca2+ from intracellular stores. The second phase of the response lasts for several minutes; its maximum amplitude is reached 1-2 min after the brief initial PAF stimulation. This phase, suppressed in zero external Ca2+ and increased in 10 mM Ca2+, is probably due to influx of Ca2+ through the plasma membrane. This secondary Ca2+ increase is blocked by 10-50 microM lanthanum. At low PAF concentration, the initial Ca2+ transient is not followed by a second phase, showing that the initial rises of Ca2+ and of its activator (presumably inositol trisphosphate) are not sufficient to trigger the second phase of Ca2+ increase.
Randriamampita
C
C
Laboratoire de Neurobiologie, Ecole Normale Supérieure, Paris, France.
Trautmann
A
A
D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002478:Cells, Cultured; D005453:Fluorescence; D007700:Kinetics; D007811:Lanthanum / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D010507:Periodicity; D010972:Platelet Activating Factor / Q000494:pharmacology*
D015220:Calcium Channels; D010972:Platelet Activating Factor; D007811:Lanthanum; D002118:Calcium