Biphasic increase in intracellular calcium induced by platelet‐activating factor in macrophages

Abstract

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 /~M Ca z+ at high PAF concentration. The amplitude of this peak is independent of extracellular Ca z÷ concentration, suggesting that the initial Ca 2÷ transient is due to the release of Ca 2÷ 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 Ca 2÷ and increased in 10 mM Ca z+, is probably due to influx of Ca 2÷ through the plasma membrane. This secondary Ca 2÷ increase is blocked by 10-50/tM lanthanum. At low PAF concentration, the initial Ca z+ transient is not followed by a second phase, showing that the initial rises of Ca 2÷ and of its activator (presumably inositol trisphosphate) are not sufficient to trigger the second phase of Ca 2÷ increase.

The Role of Calcium and Phosphorylation of Cytosolic Phospholipase A2 in Regulating Arachidonic Acid Release in Macrophages

“…PAF led to a similar degree of MAPK activation and cPLA 2 phosphorylation as ATP but it induced a more sustained increase in [Ca 2ϩ ] i . In macrophages, PAF has been reported to induce a biphasic increase in [Ca 2ϩ ] i , an initial phase due to release from intracellular stores and a second phase, due to influx of extracellular calcium (27). The results suggest that the more sustained increase in calcium is contributing to the ability of PAF to induce a low level of arachidonic acid release.…”

Spatial and Temporal Dynamics of T Cell Receptor Signaling with a Photoactivatable Agonist

“…In contrast, the delay prior to calcium flux increased with agonist dilution; this relationship has been observed for calcium signaling in other cell types (Randriamampita and Trautmann, 1989;Wang et al, 1995). Interestingly, CD4 blockade also increased the offset time for calcium flux and altered the magnitude but not the speed of LAT phosphorylation.…”

Ca2+ signals and T lymphocytes “New mechanisms and functions in Ca2+ signalling”

“…A second and related characteristic of the lymphocyte Ca 2+ signalling system is the slowness of the Ca 2+ rise. With a maximal, instantaneous stimulation (for instance, with anti-CD3 antibodies), the Ca 2+ rising phase -essentially due to Ca 2+ influx -lasts for about 30 seconds (Donnadieu et al, 1992a), whereas the Ca 2+ response of a macrophage, for instance, would reach its peak -due to Ca 2+ release-, in a fraction of second (Randriamampita and Trautmann, 1989).…”