Effect of NO• on p38 MAPK phosphorylation. Differentiated U937 cells (5 × 10 6) were incubated with S-nitrosoglutathione (GSNO; 0–400 μM) for 30 min; cells were then lysed for Western blotting to detect total (p38) and phosphorylated forms (pp38) p38 MAPK. (A) Representative gel for Western blotting. (B) Western blotting results were quantified with laser densitometry and expressed as ratios relative to control values (GSNO = 0 μM). Data are means ± SE of three independent experiments.