Cultured Epithelial Cells Release Cyclooxygenase-Dependent and Cyclooxygenase-lndependent Factors That Inhibit Cholinergic Contraction of Canine Airway Smooth Muscles

Abstract

We observed the effects of supernatants from cultured epithelial cellson the contraction of tracheal smooth muscle evoked by acetylcholine (ACh) or by electrical field stimulation (EFS). Cultured canine tracheal epithelial cells were incubated in Krebs solution with or without indomethacin (10^-5 M) for 30 and 120 min. The amplitude of the tracheal smooth muscle contractions evoked by EFS or exogenously applied ACh were measured before and after the application of each supernatant in the combined presence of both indomethacin (10^-5M) and propranolol (10^-6 M). The control supernatant incubated without indomethacin markedly suppressed the amplitude of the contraction evoked by EFS, but not by ACh. The supernatant incubated with indomethacin for 30 min did not show any effects on the contractile responses evoked by EFS or ACh. However, the supernatants from the cultured epithelial cells incubated for a longer period (120 min) in the presence of indomethacin significantly suppressed the contraction evoked by EFS, but not by ACh. The prostaglandin E₂ (PGE₂) concentration was markedly higher in the supernatants incubated without indomethacin (1.39 ± 0.51 ng/ ml, 30 min incubation) than in those with indomethacin (0.02 ± 0.01 ng/ml, 30 min incubation, and 0.06 ± 0.01 ng/ml, 120 min incubation). To determine whether PGE₂ is responsible for the inhibitory effect of the supernatants, we evaluated the effects of PGE₂ on the resting tone, and EFS- or ACh-evoked contraction. 10^-12 to 10^-6M of PGE₂ showed no significant effect on the resting tone. 10^-9 M of PGE₂, corresponding to the concentration of the supernatants incubated without indomethacin, and 10^-11M of PGE₂, to that of the supernatants incubated with indomethacin, showed a similar extent of inhibitory effects to the corresponding supernatants on the EFS-evoked contraction, and no effect on the ACh-evoked contraction. These results suggest that cultured airway epithelial cells release at least two factors spontaneously even without stimulation. One of these factors may be prostanoid (PGE₂), which acts prejunctionally to inhibit the contractile response. The other factor is distinct from prostanoid and inhibits smooth muscle contraction, presumably by suppressing ACh release from vagus nerve termini.

Regulation of smooth muscle contractility by the epithelium in rat tracheas: role of prostaglandin E2 induced by the neurotransmitter acetylcholine

“…In our study, however, the administration of indomethacin or L-NNA did not significantly alter the basal tone in rat tracheal rings, which indicated that the basal production of prostanoids and NO was low in rat airways as described previously (35). Our study also demonstrated that either pretreatment with indomethacin A B or exogenously applied PGE 2 significantly attenuated the inhibitory effect of ACh on EFS-evoked contraction of rat tracheas, which is consistent with previous reports in canine airways (36). These observations suggested that ACh might trigger the release of PGE 2 , which acted on tracheal smooth muscle and induced relaxation.…”

The airway epithelium: Structural and functional properties in health and disease

“…The prostaglandins PGE 2 , PGI 2 and small amounts of PGF 2α and TxA 2 are all produced in airway epithelium following activation of cyclooxygenase enzymes, with PGE 2 being produced in the greatest amounts. PGE 2 is generally described as a bronchoprotective mediator due to its inhibitory effects on airway smooth muscle, mucus secretion and nerve activity 72–75 . However, PGE 2 may also promote a Th‐2 bias for intraepithelial dendritic cells, suggesting that it has complex effects within the airways 76…”

“…PGE 2 is generally described as a bronchoprotective mediator due to its inhibitory effects on airway smooth muscle, mucus secretion and nerve activity. [72][73][74][75] However, PGE 2 may also promote a Th-2 bias for intraepithelial dendritic cells, suggesting that it has complex effects within the airways. 76 Originally, it was thought that bone-marrow derived cells were the main cells expressing lipoxygenase enzymes.…”