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 (DeltaI(SC)) in SGC monolayers in Ussing chambers. Dexamethasone (1 microM) or indomethacin (5 muM) during zymosan exposure of AMs reduced or abolished the supernatant-induced DeltaI(SC). Zymosan exposure induced a 5-fold increase in cyclooxygenase (COX)-2 but not COX-1 protein levels in AMs. Prostaglandin E(2) (PGE(2)) concentration in the supernatant from zymosan-activated AMs was 550 +/- 10 nM (n = 3) compared with 28 +/- 3 nM for unstimulated AMs (n = 3). PGE(2), applied serosally, induced DeltaI(SC) with an EC(50) of 15.5 +/- 1.3 nM (n = 4) and 3.6 +/- 1.8 microM (n = 3) when applied apically. Four types of endoprostanoid receptors (EP(1-4)) were detected in SGCs using Western blot. PGE(2)-induced DeltaI(SC) were inhibited by AH6809 (6-isopropoxy-9-oxoxanthene-2-carboxylic acid) but not by SC19220 (8-chloro-dibenzo[b,f][1,4]oxazepine-10(11H)-carboxylic acid, 2-acetylhydrazide), suggesting that endoprostanoid (EP)(2) but not EP(1) receptors were activated by PGE(2). Pretreatment of SGCs with supernatant from zymosan-activated AMs, PGE(2), or forskolin enhanced the sensitivity to acetylcholine (ACh)-induced DeltaI(SC). PGE(2)-induced DeltaI(SC) were blocked by charybdotoxin (ChTX), chromanol 293B, or glibenclamide. ACh-induced DeltaI(SC) were only blocked by ChTX or glibenclamide. None of these blockers altered PGE(2) pretreatment-induced sensitization of ACh-induced DeltaI(SC). These results demonstrate that prostanoids released from activated AMs directly increase cystic fibrosis transmembrane conductance regulator and K(+) channel activity. ACh-induced DeltaI(SC) are also enhanced due to enhanced activation of Ca(2+)-activated K(+) channels (K(Ca)).

Regulation of acetylcholine-induced phosphorylation of PLD1 in porcine tracheal smooth muscle.

The muscarinic agonist, acetylcholine (ACh), stimulates phospholipase D (PLD) activity in tracheal smooth muscle cells. Direct activation of protein kinase C (PKC) by phorbol-12-myristate-13-acetate (PMA) also stimulates PLD in this tissue. Activation of ACh-induced PLD was inhibited by the tyrosine kinase inhibitor genistein in a concentration-dependent manner. Presently known isoforms of PLD, PLD1 and PLD2, were identified in tracheal smooth muscle and their activation-induced phosphorylation status studied. Both ACh and PMA increased phosphorylation of PLD1 that was significantly blocked by genistein or the PKC inhibitor calphostin C. PLD2 phosphorylation was not detected in the present experiments. Western blots probed with an anti-phosphotyrosine antibody indicate that PLD1 in this tissue is phosphorylated on tyrosine residues after ACh or PMA stimulation. Tyrosine phosphorylation of PLD1 was blocked by genistein and calphostin C. No tyrosine residues were phosphorylated on PLD2. Taken together, these results demonstrate that porcine tracheal smooth muscle cells express both isoforms PLD1 and PLD2. However, on muscarinic activation only PLD1 in this tissue is phosphorylated by PKC via a tyrosine-kinase-dependent pathway.