Fig. 1. Time course of MAPK phosphorylation by phenylephrine (PHE) in the amphibian heart. ERK (Ai), JNK (Bi) and p38-MAPK (Ci) phosphorylation was assessed by western immunoblotting in samples (50 µg, 100 µg and 100 µg of protein, respectively) from control (C) Rana ridibunda hearts and hearts perfused with 50 µmol l^-1 PHE for the times indicated, using the respective phospho-specific antibodies. Total (phosphorylation state-independent) levels of ERK, JNK1 or p38-MAPK were also assessed using respective antibodies, as described in Materials and methods (Aii-Cii). Western blots are representative of three independent experiments. Bands were quantified by laser scanning densitometry and plotted (Aiii-Ciii). Values are means ± S.E.M. for the relative time points (N=3 separate heart perfusions at each time point). Values significantly different from controls: ^*P<0.05, ^**P<0.01, P<0.001.