Expression and function of endothelins, endothelin receptors, and endothelin converting enzyme in the porcine trachea

Endothelins (ETs) can modulate the airway smooth muscle tone. Using simultaneous measurements of cytosolic Ca2+ concentration ([Ca2+](i)) and tension as well as the reverse transcription polymerase chain reaction (RT-PCR), we examined ET systems in the porcine trachea. In the functional study, the application of ET-1, ET-3 or sarafotoxin S6c (S6c) caused increases in [Ca2+](i) and tension, in a concentration-dependent manner. These ET ligands were found to increase the Ca2+ sensitivity of the myofilament of the tracheal smooth muscle cells (SMCs). The contractions induced by ET-1 (10(-7) M), an ET receptor (ET-R) non-selective agonist, were much greater than those induced by S6c, an ETB-R selective agonist. BQ-123 (10(-6) M), an ETA-R antagonist, inhibited the ET-1 induced contraction. These functional experiments suggested the presence of both functioning ETA- and ETB-Rs in tracheal SMCs. RT-PCR experiments revealed that the tracheal SMCs expressed both ETA-R and ETB-R mRNAs, while tracheal epithelial cells (EpCs) predominantly expressed ETA-R mRNA. The porcine tracheal SMCs and EpCs also expressed prepro ET-1 (ppET-1), ppET3, and endothelin converting enzyme-1 (ECE-1) mRNAs. These results suggested that ETs induce contraction of porcine tracheal SMCs not only by increasing [Ca2+](i) but also increasing the Ca2+ sensitivity of the myofilament and that ETs could potentially be the autocrine and/or paracrine transmitters to regulate the contraction in the porcine airway smooth muscle.