IL-1β signaling in cat lower esophageal sphincter circular muscle

In a cat model of acute experimental esophagitis, resting in vivo lower esophageal sphincter (LES) pressure and in vitro tone are lower than in normal LES, and the LES circular smooth muscle layer contains elevated levels of IL-1 beta that decrease the LES tone of normal cats. We now examined the mechanisms of IL-1 beta-induced reduction in LES tone. IL-1 beta significantly reduced acetylcholine-induced Ca2+ release in Ca2+-free medium, and this effect was partially reversed by catalase, demonstrating a role of H2O2 in these changes. IL-1 beta significantly increased the production of H2O2, and the increase was blocked by the p38 MAPK inhibitor SB-203580, by the cytosolic phospholipase A(2) (cPLA(2)) inhibitor AACOCF3, and by the NADPH oxidase inhibitor apocynin, but not by the MEK1 inhibitor PD-98059. IL-1 beta significantly increased the phosphorylation of p38 MAPK and cPLA(2). IL-1 beta-induced cPLA2 phosphorylation was blocked by SB-203580 but not by AACOCF3, suggesting sequential activation of p38 MAPK-phosphorylating cPLA2. The IL-1 beta-induced reduction in LES tone was partially reversed by AACOCF3 and by the Ca2+-insensitive PLA(2) inhibitor bromoenol lactone (BEL). IL-1 beta significantly increased cyclooxygenase (COX)-2 and PGE(2) levels. The increase in PGE(2) was blocked by SB-203580, AACOCF3, BEL, and the COX-2 inhibitor NS-398 but not by PD-98059 or the COX-1 inhibitor valeryl salicylate. The data suggested that IL-1 beta reduces LES tone by producing H2O2, which may affect Ca2+-release mechanisms and increase the synthesis of COX-2 and PGE2. Both H2O2 and PGE2 production depend on sequential activation of p38 MAPK and cPLA2. cPLA(2) activates NADPH oxidases, producing H2O2, and may produce arachidonic acid, converted to PGE(2) via COX-2.