Fig. 6. Inhibition of DC electrical-field-induced c-Fos induction in multicellular tumor spheroids by suramin and anion channel antagonists. (A) Representative tumor spheroids immunolabeled with an antibody directed against Fos protein. Multicellular tumor spheroids remained untreated (control) (Aa) or were treated with a single electrical field pulse (750 Vm^-1, 60 seconds) in the absence (Ab) or presence of either suramin (300 µM) (Ac) or the anion channel inhibitors niflumic acid (200 µM) (Ad), tamoxifen (50 µM) (Ae), and NPPB (50 µM) (Af). They were subsequently immersed in cell culture medium in the absence of the compounds and fixed after 1 hour of incubation. Bar, 75 µm. (B) Quantitative evalulation of Fos immunofluorescence in control and electrical-field-treated samples. Note that in the presence of suramin or anion channel blockers the induction of c-Fos following electrical field treatment was significantly inhibited.