ENDOTHELIN STIMULATES CHLORIDE SECRETION ACROSS CANINE TRACHEAL EPITHELIUM

The endothelins (ET) are a group of isopeptides produced by a number of cells, including canine tracheal epithelial cells. Because these compounds are endogenous peptides that may activate eicosanoid metabolism, we investigated the effects of ET on Cl secretion in canine tracheal epithelium. Endothelin 1 (ET-1) was found to produce a dose-dependent change in short-circuit current (I(sc)) that increased slowly and reached a maximal value within 10-15 min. When isopeptides of ET were compared, 300 nM ET-1 and ET-2 produced comparable maximal increases in I(sc), whereas ET-3 produced smaller changes in I(sc) (half-maximal concentrations of 2.2, 7.2, and 10.4 nM, respectively). Ionic substitution of Cl with nontransported anions, iodide and gluconate, reduced ET-1-induced changes in I(sc). Furthermore, the response was inhibited by the Na-Cl cotransport inhibitor, furosemide. In paired tissues, ET-1 significantly increased mucosal net Cl-36 flux without significant effect on Na-22 flux. The increase in I(sc) induced by ET was diminished by pretreatment with indomethacin. The second messengers mediating the increase in I(sc) were investigated in cultured canine tracheal epithelial cells. ET-1 stimulated the release of [H-3]arachidonate from membrane phospholipids, increased intracellular Ca2+ (occasionally producing oscillations), and increased adenosine 3',5'-cyclic monophosphate accumulation. The latter was diminished by indomethacin. Thus ET is a potent agonist of Cl secretion (with the isopeptides having the following potency: ET-1 greater-than-or-equal-to ET-2 > ET-3) and acts, in part, through a cyclooxygenase-dependent mechanism.