Involvement of Rho‐kinase in contraction of guinea‐pig aorta induced by prostanoid EP 3 receptor agonists

The mechanism of contraction of guinea‐pig isolated aorta induced by the prostanoid EP 3 receptor agonist sulprostone (0.1–300 n M ) has been investigated. In 60% of the experiments, the sulprostone log concentration–response curve (maximum=15–40% of 100 n M U‐46619 response; low‐responders ) was unaffected by the removal of extracellular Ca 2+ , blockade of L‐type Ca 2+ channels with nifedipine and depletion of internal Ca 2+ stores. In the remaining preparations (35–65% of 100 n M U‐46619 response; high‐responders ), contractions to higher sulprostone concentrations showed a nifedipine‐sensitive component, which was enhanced by charybdotoxin. In Ca 2+ ‐free Krebs solution, established contractions to 300 n M sulprostone were abolished by the Rho‐kinase inhibitors H‐1152, Y‐27632 and HA‐1077 (IC 50 values=190, 770 and 2030 n M ). The PKA/Rho‐kinase inhibitor H‐89 (10 n M –10 μ M ) caused enhancement progressing to inhibition. The selective PKC inhibitor Ro 32‐0432 (3 μ M ) had no effect, while staurosporine, recently shown to be a potent Rho‐kinase inhibitor, abolished sulprostone responses (IC 50 ∼47 n M ), but its action was slow. The MAP kinase inhibitors SB 202190, SB 203580 and PD 80958 produced little inhibition. In normal Krebs solution, H‐1152 and Y‐27632 abolished established contractions to 300 n M sulprostone and 1 μ M phenylephrine, and partially inhibited 10 μ M phenylephrine and 50 m M K + responses. The results are discussed in relation to the reported potencies of the protein kinase inhibitors in enzyme assays. Activation of the Rho‐kinase pathway appears to be a primary mechanism of contraction induced by EP 3 receptor agonists in guinea‐pig aorta.British Journal of Pharmacology (2003) 139 , 1449–1461. doi: 10.1038/sj.bjp.0705393