Platelet-activating factor–induced calcium mobilization and oxidative metabolism in hepatic macrophages and endothelial cells

Abstract

Fluorescence image analysis of the calcium sensitive dye Indo-1 was used to characterize platelet-activating factor (PAF)-induced calcium mobilization in hepatic macrophages and endothelial cells. PAF, but not lyso-PAF, an inactive analog, induced a rapid and transient increase in intracellular levels of calcium that appeared to depend on the presence of extracellular calcium. In both macrophages and endothelial cells, these effects were dose dependent, reaching maximal levels with 10 nM PAF. However, the kinetics of the calcium response to PAF in macrophages and endothelial cells was distinct. The endothelial cells responded more rapidly to PAF than the macrophages (within 1 min vs. 2-3 min, respectively) and displayed longer recovery periods (4 min vs. > 10 min, respectively). In contrast, the magnitude of the response to PAF was greater in the macrophages. In both cell types, triazolam and alprazolam, two PAF antagonists, and the calcium channel blocker verapamil inhibited PAF-induced calcium mobilization. PAF also stimulated superoxide anion production alone and in combination with the macrophage activator 12-O-tetradecanoyl-phorbol-13-acetate (TPA) in both cell types. Macrophages produced more of this reactive oxygen intermediate in response to PAF and TPA than endothelial cells. Interestingly, in the absence of extracellular calcium or when verapamil was added to the cultures, superoxide anion production by the macrophages, but not the endothelial cells, was significantly reduced. These results demonstrate that, although hepatic macrophages and endothelial cells mobilize calcium in response to PAF, the characteristics of the response in each cell type are different. These differences may underlie, at least in part, distinct functional responses of the cells to PAF.

Platelet-Activating Factor Involvement in Thioacetamide-Induced Experimental Liver Fibrosis and Cirrhosis

“…It has, moreover, been shown that PAF stimulated perfused liver, isolated Kupffer and hepatic endothelial cells to release superoxide anion [55,56]. These observations are in accordance with our results, which showed oxidative stress occurrence through increased production of MDA in the liver tissue.…”

Macrophages and Tissue Injury: Agents of Defense or Destruction?

“…PAF is thought to act in a paracrine and autocrine manner to amplify and propagate early stages of the inflammatory response. PAF released from macrophages stimulates phagocyte chemotaxis and oxidative metabolism (141, 142). In the lung, PAF mediates ozone-induced airway inflammation, microvascular leakage, and edema (143, 144).…”

Critical Role of NADPH Oxidase-derived Reactive Oxygen Species in Generating Ca2+ Oscillations in Human Aortic Endothelial Cells Stimulated by Histamine

“…Whereas the oxidase of phagocytes generates large quantities of ROS that are necessary to eliminate engulfed microorganisms, the NADPH oxidase of non-phagocytic cells generates low levels of ROS that appear to have a cell signaling function. ROS generation by endothelial cells has been observed after stimulation by acetylcholine (15), interleukin-4 (16), interleukin-1 (17), interferon-␥ (17), bradykinin (18,19), platelet-activating factor (20), vascular endothelial growth factor (21), tumor necrosis factor (22)(23)(24)(25), angiotensin II (26,27), and thrombin (28). In several circumstances, this ROS production has been shown to result from activation of endothelial NADPH oxidase (24,27,28).…”