SPECIFIC BINDING OF ENDOTHELIN-1 TO CANINE TRACHEAL EPITHELIAL-CELLS IN CULTURE

We have studied the binding of endothelin-1 (ET-1) to cultured canine tracheal epithelial cells. A single specific binding site for I-125-la beled ET-1 was identified with an apparent dissociation constant (K-d) of 0.2 nM, maximal binding sites (B-max) of 6.7 x 10(3) sites/cell, a nd half-maximal inhibition (IC50) of 0.3 nM during a 2-h incubation pe riod. The binding of I-125-ET-1 to these cells was inhibited by the pr esence of unlabeled ET-1, ET-2, or BQ-123, whereas ET-3 and sarafotoxi n S6c did not compete for this binding site. These binding characteris tics are consistent with those of the ETA receptor. At 37 degrees C, s pecific binding continuously increased over 18 h, while at 4 degrees C , it reached a plateau by 2 h. The increase in binding at 37 degrees C was not associated with DNA synthesis but was dependent upon protein synthesis, suggesting that epithelial binding sites were produced cont inuously under these incubation conditions. Our results indicate that canine tracheal epithelial cells possess specific binding sites for ET -1 with characteristics similar to those of the ETA receptor subtype. Because these cells are demonstrated to both release and bind ET-1, th e results further suggest that ET-1 is involved in paracrine and/or au tocrine control mechanisms in the airway epithelium.