Silica increases cytosolic free calcium ion concentration of alveolar macrophages in vitro

Abstract

Rat alveolar macrophages were exposed to silica dust (quartz) suspended in culture medium (SiO 2, dry particle size less than 5 μm in diameter) and fluctuation in their cytosolic free calcium content ([Ca 2+]i) was detected in cell monolayers with a fluorescent calcium probe (Indo-1AM). Cytosolic free calcium content was correlated with lactate dehydrogenase (LDH) release, an index of cell damage. SiO 2 induced a concentration- and time-dependent increase of cytosolic free Ca 2+ ion concentration and LDH release. [Ca 2+]i was increased about fivefold when cells were exposed to 200 μg of SiO 2 per milliliter (3 ml per dish) for 2 hr. [Ca 2+]i changed within 15 min of SiO 2 treatment, whereas LDH release was measurably increased only after 30 min. Chelation of extracellular Ca 2+ by 2 m m ethylene glycol bis(β-aminoethyl ether) N,N′-tetraacetate did not prevent SiO 2-induced fluctuation of macrophage [Ca 2+]i, but did partially prevent the SiO 2-induced increase in LDH release ( p < 0.01). We conclude that a very early event in SiO 2-induced damage of alveolar macrophages involves mobilization of intracellular calcium pools to increase [Ca 2+]i. These results suggest that SiO 2-induced macrophage damage, a key event in the development of silicosis, may involve perturbation of intracellular calcium homeostasis.