Immunoblotting analysis of Cl25 cells after one-hour nicotine treatment at indicated doses in 0.5% serum (A) or 5% serum (B). C, SRB assay of CL25 cells in 5% serum. Prior to nicotine treatment, OD570 values were approximately 0.1. The first bar for each time point is untreated cells. Nicotine doses (from left to right for each time point) were 1 nM, 10 nM, 100 nM, 1 µM and 10 µM. Any differences are not significant.