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

Abstract

1. The mechanism of contraction of guinea-pig isolated aorta induced by the prostanoid EP 3 receptor agonist sulprostone (0.1-300nM) has been investigated. In 60% of the experiments, the sulprostone log concentration-response curve (maximum = 15-40% of 100 nM 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 nM U-46619 response; high-responders), contractions to higher sulprostone concentrations showed a nifedipine-sensitive component, which was enhanced by charybdotoxin. 2. In Ca 2+-free Krebs solution, established contractions to 300 nm sulprostone were abolished by the Rho-kinase inhibitors H-1152, Y-27632 and HA-1077 (IC 50 values = 190, 770 and 2030 nM). The PKA/Rho-kinase inhibitor H-89 (10 nM-10 μM) caused enhancement progressing to inhibition. The selective PKC inhibitor Ro 32-0432 (3 μM) had no effect, while staurosporine, recently shown to be a potent Rho-kinase inhibitor, abolished sulprostone responses (IC 50 ∼47 nM), but its action was slow. The MAP kinase inhibitors SB 202190, SB 203580 and PD 80958 produced little inhibition. 3. In normal Krebs solution, H-1152 and Y-27632 abolished established contractions to 300nM sulprostone and l μM phenylephrine, and partially inhibited 10 μM phenylephrine and 50 mM K + responses. 4. 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.