Inhibition of myosin phosphatase by upregulated Rho-kinase plays a key role for coronary artery spasm in a porcine model with interleukin-1 beta

Background-We recently demonstrated that the Rho-kinase-mediated pathway pl ays an important role for coronary artery spasm in our porcine model with i nterleukin-1 beta (IL-1 beta). In this study, we examined whether or not Rh o-kinase is upregulated at the spastic site and if so, how it induces vascu lar smooth muscle hypercontraction. Methods and Results-Segments of the left porcine coronary artery were chron ically treated from the adventitia with IL-1 beta-bound microbeads. Two wee ks after the operation, as reported previously, intracoronary serotonin rep eatedly induced coronary hypercontractions at the IL-1 beta-treated site bo th in vivo and in vitro, which were. markedly inhibited by Y-27632, one of the specific inhibitors of Rho-kinase, Reverse transcription-polymerase cha in reaction analysis demonstrated that the expression of Rho-kinase mRNA wa s significantly increased in the spastic compared with the control segment. Western blot analysis showed that during the serotonin-induced contraction s, the extent of phosphorylation of the myosin-binding subunit of myosin ph osphatase (MBS), one of the major substrates of Rho-kinase, was significant ly greater in the spastic than in the control segment and that the increase in MBS phosphorylations was also markedly inhibited by Y-27632. There was a highly significant correlation between the extent of MBS phosphorylations and that of contractions. Conclusions-These results indicate that Rho-kinase is upregulated at the sp astic site and plays a key role in inducing vascular smooth muscle hypercon traction by inhibiting myosin phosphatase through the phosphorylation of MB S in our porcine model.