Synergistic effects of combinations of nicotine (N) with EGF (E), IGF-I (I) or VEGF (V) on proliferation of different types of lung cells. Alive, ie, TBD-negative, cells seeded at a density of 1 × 104 per well of a 96-well plate were counted after 24 h of incubation in the absence (intact control) or presence of the optimal doses of nicotine (see text) and 10 ng/ml of each test GF. Some cells were exposed to 20 μM HC-3 (H) ± nicotine and some — to nicotine/GF combinations in the presence of αBtx (B; 1 μM) and/or Mec (M; 50 μM). All values significantly (p < 0.05) differed from the intact control, taken as 100%. Data are mean + SD from a triplicate sample. Asterisk = p < 0.05 compared to nicotine alone; arrows = p < 0.05 between indicated conditions.