SILICA INDUCES CHANGES IN CYTOSOLIC-FREE CALCIUM, CYTOSOLIC PH, AND PLASMA-MEMBRANE POTENTIAL IN BOVINE ALVEOLAR MACROPHAGES

The mineral-dust induced activation of pulmonary phagocytes is thought to be involved in the induction of severe lung diseases. The activati on of bovine alveolar macrophages (BAM) by silica was investigated by flow cytometry. Shortterm incubation (<10 min) of BAM with silica gel and quartz dust particles induced increases in the cytosolic free calc ium concentration ([Ca2+](i)), decreases in intracellular pH (pH(i)), and increases in plasma membrane potential (PMP). The extent of these changes was concentration dependent, related to the type of dust and w as due to Ca2+ influx from the extracellular medium. An increase in [C a2+](i) was inhibited, when extracellular Ca2+ was removed. Furthermor e the calcium signal was quenched by Mn2+ and diminished by the calciu m channel blocker verapamil. The protein kinase C specific inhibitor b isindolylmaleimide II (GF 109203 X) did not inhibit the silica-induced [Ca2+](i) rise. In contrast, silica-induced cytosolic acidification a nd depolarization were inhibited by GF 109203 X but not by removal of extracellular calcium. Addition of TiO2 particles or heavy metal-conta ining dusts had no effect on any of the three parameters. Our data sug gest the existence of silica-activated transmembrane ion exchange mech anisms in BAM, which might be involved in the specific cytotoxicity of silica by Ca2+-dependent and independent pathways.