Prostanoids Secreted by Alveolar Macrophages Enhance Ionic Currents in Swine Tracheal Submucosal Gland Cells

We examined the effect of substances released by swine alveolar macrophages (AMs) on ionic currents in airway submucosal gland cells (SGCs). AMs obtained by lavage were activated by 24-h zymosan exposure (0.1 mg/ml). Supernatant was collected and used to stimulate short-circuit current changes (ΔISC) in SGC monolayers in Ussing chambers. Dexamethasone (1 μM) or indomethacin (5 μM) during zymosan exposure of AMs reduced or abolished the supernatant-induced ΔISC. Zymosan exposure induced a 5-fold increase in cyclooxygenase (COX)-2 but not COX-1 protein levels in AMs. Prostaglandin E2 (PGE2) concentration in the supernatant from zymosan-activated AMs was 550 ± 10 nM ( n = 3) compared with 28 ± 3 nM for unstimulated AMs ( n = 3). PGE2, applied serosally, induced ΔISC with an EC50 of 15.5 ± 1.3 nM ( n = 4) and 3.6 ± 1.8 μM ( n = 3) when applied apically. Four types of endoprostanoid receptors (EP1–4) were detected in SGCs using Western blot. PGE2-induced ΔISC were inhibited by AH6809 (6-isopropoxy-9-oxoxanthene-2-carboxylic acid) but not by SC19220 (8-chloro-dibenzo\[ b,f \]\[1,4\]oxazepine-10(11 H )-carboxylic acid, 2-acetylhydrazide), suggesting that endoprostanoid (EP)2 but not EP1 receptors were activated by PGE2. Pretreatment of SGCs with supernatant from zymosan-activated AMs, PGE2, or forskolin enhanced the sensitivity to acetylcholine (ACh)-induced ΔISC. PGE2-induced ΔISC were blocked by charybdotoxin (ChTX), chromanol 293B, or glibenclamide. ACh-induced ΔISC were only blocked by ChTX or glibenclamide. None of these blockers altered PGE2 pretreatment-induced sensitization of ACh-induced ΔISC. These results demonstrate that prostanoids released from activated AMs directly increase cystic fibrosis transmembrane conductance regulator and K+ channel activity. ACh-induced ΔISC are also enhanced due to enhanced activation of Ca2+-activated K+ channels (KCa).