Phase-contrast microscopy analysis of sidestream whole (SSW) smoke treated primary fibroblasts. Cells were treated with different doses of SSW for 18 hours. Control cells were kept in serum-free medium for the same time period because the smoke solutions are diluted in serum-free medium. (A) Untreated cells were spread out, confluent, contact inhibited, and showed prominent nuclei. (B) Cells treated with 1:9 (SSW:media) smoke dilution became elongated and separated from each other. (C) Cells treated with 1:4 SSW smoke rounded up and showed signs of cell death. (D) Cells treated with 1:9 SSW smoke solution recovered quickly; within a few hours of being in complete media they were back to normal morphology. (E) ATP assays: cells were plated in a 96 well ELISA plate, allowed to reach confluency, and treated for 18 hours with SSW. Smoke-treated cells showed a decrease in ATP production, but the overall ATP level remained high. Pictures are representative of at least 3 experiments performed with different batches of primary cells. Scale bar = 20 μm.