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 [I-125]-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 [I-125]-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 almost-equal-to scyliorhinin I > eledoisin almost-equal-to substance P almost-equal-to neurokinin A > phyllomedusin almost-equal-to 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.