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 ¹²⁵I- labeled ET-1 was identified with an apparent dissociation constant (K(d)) of 0.2 nM, maximal binding sites (B(max)) of 6.7 x 10³ sites/cell, and half- maximal inhibition (IC₅₀) of 0.3 nM during a 2-h incubation period. The binding of ¹²⁵I-ET-1 to these cells was inhibited by the presence of unlabeled ET-1, ET-2, or BQ-123, whereas ET-3 and sarafotoxin S6c did not compete for this binding site. These binding characteristics are consistent with those of the ETA receptor. At 37°C, specific binding continuously increased over 18 h, while at 4°C, it reached a plateau by 2 h. The increase in binding at 37°C was not associated with DNA synthesis but was dependent upon protein synthesis, suggesting that epithelial binding sites were produced continuously 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, the results further suggest that ET-1 is involved in paracrine and/or autocrine control mechanisms in the airway epithelium.