Ovine airway epithelial explants, cultured at an air–liquid interface, were used to determine whether endothelin (ET-1) acts via ET_A- or ET_B-receptors to increase ciliary beat frequency (CBF). Further, the role of prostanoids and nitric oxide (NO) downstream of receptor activation was explored. CBF was measured using an image analysis system with a sampling rate of 224 frames s⁻¹. At 37 °C, baseline CBF was 14.90 ± 3.49 Hz (n = 116 cells). ET-1 dose-dependently stimulated CBF (EC₅₀ = 60.98 ± 27.99 nM). The stimulatory effect of ET-1 (1 μM) could be mimicked by the ET_A-receptor agonist sarafotoxin S6b (100 nM) but not the ET_B-receptor agonist sarafotoxin S6c (100 nM) and was completely abolished by the ET_A-receptor antagonist BQ-123 (1 μM). Thus the ciliostimulatory effect of ET-1 appears to be via its interaction with ET_A receptors. Application of a combination of the cyclo-oxygenase (COX) inhibitors indomethacin (30 μM) and ibuprofen (10 μM) did not alter baseline CBF but prevented ciliostimulation by ET-1. Incubation of the explants with the nitric oxide synthase (NOS) inhibitor L-NMMA (100 μM) caused a significant decrease in CBF relative to baseline (p < 0.01) which developed over 20 min and remained stable thereafter. Subsequent perfusion of the explant with ET-1 was unable to increase CBF above the new baseline. These results suggest a role for both prostanoids and nitric oxide in ET-1-stimulated CBF.

This study has shown, for the first time, that ET-1 stimulates CBF via its interaction with ET_A-receptors. Inhibition of both COX and NOS inhibited the effect of ET-1 suggesting a role for both these enzymes in the ET-1 response downstream from the ET_A-receptor.