Binding sites for tachykinin peptides in the brain and stomach of the dogfish, Scyliorhinus canicula

In membranes of dogfish brain and stomach, two binding sites for tachykinins were identified. One site specifically bound [¹²⁵I]-Bolton-Hunter substance P (BH-SP) and the rank potency of tachykinins to compete for BH-SP binding revealed similarities with the rank potency of an NK₁ receptor. The pharmacology of the other site, which specifically bound [¹²⁵I]-Bolton-Hunter scyliorhinin II (BH-Scy II), did not resemble any of the mammalian tachykinin receptors. The rank potency to inhibit BH-Scy II binding to this second site was: scyliorhinin II ≈ scyliorhinin I > eledoisin ≈ substance P ≈ neurokinin A > phyllomedusin ≈ physalaemin > [Sar⁹Met(O₂)¹¹]substance P. Neurokinin B and senktide did not displace BH-Scy II binding. In addition, nucleotide analogues inhibited BH-SP binding but not BH-Scy II binding. Our binding data suggest the existence of a mammalian-like NK₁ receptor and of a nonmammalian tachykinin receptor in the dogfish.