Increased calcium influx in a monocytic cell line on exposure to ultrafine carbon black

Ultrafine particles have been shown to induce pro-inflammatory effects both in vivo and in vitro. Increased expression of pro-inflammatory genes probably requires the activation of specific transcription factors such as nuclear factor kappa B (NF-κB) via a number of possible pathways including Ca²⁺ and reactive oxygen species. The fluorescent dye fura 2, was used to measure cytosolic Ca²⁺ in the human monocytic cell line, Monomac 6 on exposure to 66 μg·mL^-1 of either ultrafine carbon black (ufCB; diameter 14 nm), carbon black (CB; diameter 260 nm), quartz (diameter 1.45 μm), or medium alone. UfCB but not fine CB induced a 1.6-fold increase (p<0.01) in the resting cytosolic Ca²⁺ concentration of Monomac 6 cells. In addition ufCB induced a 2.6-fold increase (p<0.001) in the response to the endoplasmic reticulum Ca²⁺- adenosine triphosphatase (ATPase) inhibitor, thapsigargin, suggesting the Ca²⁺ release-activated Ca²⁺ current across the plasma membrane was enhanced. This response was inhibited by the removal of extracellular Ca²⁺ and by the Ca²⁺ channel blocker, verapamil. In addition, ufCB stimulated the entry of extracellular Mn²⁺. Finally, the antioxidants mannitol and nacystelin both inhibited the effects of ufCB on the response to thapsigargin. These data suggest that ultrafine carbon black particles stimulated an increase in cytosolic Ca²⁺, possibly through the entry of extracellular Ca²⁺ via Ca²⁺ channels in the plasma membrane. The particles may in part activate the opening of Ca²⁺ channels via a mechanism involving reactive oxygen species. (C) ERS Journals Ltd. 2000.