Fig. 3. Effect of - and ß-adrenergic antagonists on p38-MAPK stimulation by phenylephrine (PHE). (A) p38-MAPK phosphorylation was assessed by western immunoblotting in samples (100 µg of protein) from control Rana ridibunda hearts and hearts perfused with 50 µmol l^-1 PHE in the presence or absence of 1 µmol l^-1 prazosin (PZ) (Ai), 1 µmol l^-1 phentolamine (PHT) (Aii), 1 µmol l^-1 yohimbine (YOH) (Aiii) and 1 µmol l^-1 propranolol (PRO) (Aiv). Western blot analysis was performed as described in Materials and methods. Identical samples were also assayed for total p38-MAPK immunoreactivity (B). Each experiment was repeated on two further occasions with similar results. Bands were quantified by laser scanning densitometry and plotted (C). Asterisks indicate values significantly different from controls: ^*P<0.05, ^**P<0.01.