Study of direct adsorption of A23187 onto particles. (a) 16HBE cells were exposed 4 h to 10 μg/cm2 PM2.5-AW prior to addition of 3 μM A23187 during 20 supplementary hours. (b) To avoid possible adsorption, PM2.5-AW were removed and cells were washed five times with PBS before drug treatment. (c) Particles and A23187 were co-incubated 4 h into a coated 24 wells-plate without cells, and then supernatant was used to trigger apoptosis for 20 h supplementary. ΔΨm dissipation was measured by flow cytometry and results are expressed as percentage of apoptosis induction as described in Materials and Methods section. Results are means ± S.D (n = 3). Significance was calculated for PM2.5-AW + A23187 versus A23187 alone for all conditions with p < 0.05 (*) or for PM2.5-AW + A23187 treatment with respect to a, b or c condition (#, p < 0.05).