Fig. 1. Activation of p43-ERK by H₂O₂. (A) Top panel: R. ridibunda hearts were perfused in the absence (C) or presence of 100 µmol l^-1 H₂O₂ for the times indicated, and phosphorylation of p43-ERK (50 µg of protein) was assessed by immunoblot. Bottom panel: an immunoblot of identical samples for total p43-ERK levels was included as a control for protein loading. (C) H₂O₂ dose-dependent activation of p43-ERK. Hearts were perfused with 3–1000 µmol l^-1 H₂O₂ for 5 min. As positive controls, extracts from hearts perfused with 1 µmol l^-1 PMA for 10 min were included. Blots are representative of three independent experiments. (B,D) Densitometric analysis of phospho-p43-ERK bands by laser scanning. Results are means ± S.E.M. for three independent experiments performed with similar findings. ^*P<0.05, ^**P<0.01 vs control value.