Silica Induces Changes in Cytosolic Free Calcium, Cytosolic pH, and Plasma Membrane Potential in Bovine Alveolar Macrophages

Abstract

The mineral‐dust induced activation of pulmonary phagocytes is thought to be involved in the induction of severe lung diseases. The activation of bovine alveolar macrophages (BAM) by silica was investigated by flow cytometry. Short‐term incubation (10 min) of BAM with silica gel and quartz dust particles induced increases in the cytosolic free calcium concentration ([Ca2+]i), decreases in intracellular pH (pHi), and increases in plasma membrane potential (PMP). The extent of these changes was concentration dependent, related to the type of dust and was due to Ca2+ influx from the extracellular medium. An increase in [Ca2+]i was inhibited, when extracellular Ca2+ was removed. Furthermore the calcium signal was quenched by Mn2+ and diminished by the calcium channel blocker verapamil. The protein kinase C specific inhibitor bisindolylmaleimide II (GF 109203 X) did not inhibit the silica‐induced [Ca2+]i rise. In contrast, silica‐induced cytosolic acidification and depolarization were inhibited by GF 109203 X but not by removal of extracellular calcium. Addition of TiO2 particles or heavy metal‐containing dusts had no effect on any of the three parameters. Our data suggest the existence of silica‐activated transmembrane ion exchange mechanisms in BAM, which might be involved in the specific cytotoxicity of silica by Ca2+‐dependent and independent pathways.

Size-Dependent Proinflammatory Effects of Ultrafine Polystyrene Particles: A Role for Surface Area and Oxidative Stress in the Enhanced Activity of Ultrafines

“…Transcription factor activation may be mediated in part by changes in calcium ion homeostasis, leading to the expression of proinflammatory genes (Dolmetsch et al, 1998). Ultrafine polystyrene thus joins asbestos (Faux et al, 1994) and quartz (Tarnock et al, 1997) in a list of pathogenic particles that modulate intracellular calcium (Faux et al, 1994;Lim et al, 1997) and these Ca 2ϩ changes are very likely related to the oxidative stress that the particles generate (Hoyal et al, 1998;Stone et al, 2000).…”

Autocrine abscisic acid plays a key role in quartz‐induced macrophage activation

“…The identity of the ROS‐activated Ca 2+ channel responsible for the ABA‐induced Ca 2+ influx and whether it is the same channel activated by the quartz radicals (Fig 4, channels a, b ) remain to be established. Inhibitors of voltage‐gated Ca 2+ channels, known to down‐regulate the quartz‐triggered [Ca 2+ ] i increase in human polymorphonuclear leukocytes (45) and in bovine alveolar macrophages (46), did not affect the calcium response of RAW264.7 cells to quartz (data not shown). The Ca 2+ ‐permeable plasma membrane channel TRPM2 could be a reasonable candidate as the quartz‐ and/or ABA‐activated channel because it is known to be opened by oxidative stress (47) and to be responsible for NF‐κB‐dependent chemokine production in monocytes (48, 49).…”

Pulmonary Toxicity of Silica Linked to Its Micro- or Nanometric Particle Size and Crystal Structure: A Review

“…Phagocytosis is a critical mechanism through which innate immune cells eliminate microbes, necrotic or apoptotic cells, and mineral particles, such as crystalline silica. Expression levels for various markers of activated phagocytosis have been reported to be altered after exposure to microcrystalline silica: significant increase in lysosomal enzymes NAG ( N -acetyl glucosaminidase) [ 20 , 23 ] and glucuronidase [ 23 ], heightened levels of extracellular cathepsins (L, B, V) and intracellular cathepsin B [ 51 ] and cathepsin K [ 50 ], increased free cytosolic Ca 2+ concentration and plasma membrane potential in bovine macrophages exposed to microcrystalline silica, and significantly decreased pHi [ 129 ]. However, phagocytosis could also be impaired by microcrystalline silica.…”