Fig. 4. Activation of p38-MAPK by H₂O₂. (A) Protein (100 µg) from R. ridibunda hearts perfused in the absence (C) or presence of 100 µmol l^-1 H₂O₂ for the times indicated was assessed by immunoblot using phosphospecific anti-p38-MAPK antibody (top panel) or total anti-p38-MAPK antibody (bottom panel). (C) Hearts were perfused with increasing concentrations of H₂O₂ (3–1000 µmol l^-1) for 2 min. As positive controls, extracts from hearts perfused with 0.5 mol l^-1 sorbitol (S) for 15 min were included. Blots are representative of four independent experiments. (B,D) Densitometric analysis of phospho-p38-MAPK bands by laser scanning. Results are means ± S.E.M. for four independent experiments. ^*P<0.05, ^**P<0.01, P<0.001 vs control value.