Effects of apocynin on phenylephrine-induced MYPT1 phosphorylation. RTA strips were pre-incubated with apocynin or vehicle for 30 min and then challenged with phenylephrine for 1 or 15 min. Phosphorylation levels of MYPT1 at Thr697 (a) and Thr855 (b) were assessed by immunoblotting using phospho-specific MYPT1 antibody. Equal protein loading was verified by total MYPT1 immunoreactivity. The upper panels show representative immunoblots and the lower panels summarize the densitometric results. Values were normalized against control and data are presented as mean ± S.E.M. of four independent experiments. *p < 0.05 vs. control; #p < 0.05 compared with time-matched phenylephrine alone.