Characterization of an endothelin ET sub(B) receptor in the gill of the dogfish shark Squalus acanthias

摘要

Endothelins (ETs) are potent vasoconstrictive peptides that are secreted by the vascular endothelium and other tissues in vertebrates. Previous studies have demonstrated that ETs are expressed in a variety of fish tissues and contract various blood vessels. In order to determine if receptors for ET are expressed in fish gill tissue, we examined the binding kinetics of super(125)I-labeled, human ET-1 to membrane fragments isolated from the gill of the dogfish shark, Squalus acanthias. super(125)I-ET-1 bound at a single site, with a dissociation constant (K sub(d)) and binding site number (B sub(max)) very similar to those described in a variety of mammalian blood vessels. ET-1 and ET-3 competed equally with super(125)I-ET-1, suggesting that the receptor was ET sub(B), which has been shown in mammalian systems to bind to both ligands equally. The ET sub(B)-specific agonists sarafotoxin S6c, IRL-1620, and BQ-3020 also competed against super(125)I-ET-1 at a single site, supporting this hypothesis. We conclude that the shark gill expresses an ET sub(B) receptor with substantial homology to the mammalian receptor and that ET may play an important role in modulating such vital gill functions as gas exchange, ion regulation, acid-base balance, and excretion of nitrogen.