Prostaglandin E2-prostanoid EP3 signal induces vascular contraction via nPKC and ROCK activation in rat mesenteric artery

Prostaglandin E2 (PGE2) is one major prostanoid produced under inflammatory situation. Although PGE2 is known to induce vascular contraction, its detailed mechanism remains unknown. In the present study, we investigated the signaling pathway underlying PGE2-induced smooth muscle contraction in rat mesenteric artery. PGE2 (0.3-30 μM) concentration-dependently caused contraction in endothelium-denuded artery. RT-PCR showed that this artery expresses mRNAs for all four prostanoid EP receptors (prostanoid EP1-4). Among selective agonists for PGE2 receptors, only a prostanoid EP3 receptor agonist, ONO-AE-248 (0.3-30 μM) induced contraction. Consistently, pretreatment with a prostanoid EP3 antagonist (L-798106, 1 μM) significantly but not completely inhibited the PGE2-induced contraction. Interestingly, pretreatment with a prostanoid FP antagonist (AL8810, 1 μM) or a TP antagonist (SQ29548, 10 nM) also partially inhibited the PGE2-induced contraction. Since ONO-AE-248 (10 μM) did not influence intracellular Ca2+ concentration in mesenteric artery, we next examined the involvement of Ca2+-independent contractile pathway including PKCs and ROCK in prostanoid EP3-mediated contraction. Pretreatment with bisindolyl-maleimide I (a general PKC inhibitor, 1 μM), Ro-31-8425 (a conventional PKC and PKCε inhibitor, 1 μM), rottlerin (a selective PKCδ inhibitor, 1 μM) and Y-27632 (a ROCK inhibitor, 1 μM) but not Go 6976 (a conventional PKC inhibitor, 1 μM) attenuated 10 μM ONO-AE-248-induced vascular contraction. In western blot analysis, we confirmed that the treatment with ONO-AE-248 (10 μM, 30 min) phosphorylated PKCδ (Thr505) and PKCε (Ser729). These results suggest that PGE2 induces vascular smooth muscle contraction via prostanoid EP3, FP and TP receptors in rat mesenteric artery. Prostanoid EP3-mediated contraction is ascribed to Ca2+-independent contractile pathway including PKCδ, ε and ROCK.