Characterization and autoradiographic localization of multiple tachykinin binding sites in gastrointestinal tract and bladder.

Binding sites for the [125I]Bolton-Hunter-labeled tachykinins substance K (BHSK), eledoisin (BHE) and substance P (BHSP) were investigated using crude membrane suspensions and autoradiography. In smooth muscle membranes from guinea-pig small intestine and rat duodenum, specific binding of BHSK was saturable and reversible, showing a single class of sites with a KD of 1 to 3 nM and maximum number of specific binding sites of 1 to 2 fmol/mg of wet weight tissue. Pharmacological characterization of this binding revealed a novel receptor site (K) with affinity for substance K greater than kassinin greater than or equal to eledoisin greater than neuromedin K greater than substance P greater than physalaemin. Inhibition of the binding of BHSK in membranes from mouse urinary bladder exhibited a similar K-type pattern. In rat duodenum and mouse bladder membranes, the binding of BHE was inhibited by substance K greater than kassinin greater than eledoisin greater than neuromedin K greater than substance P greater than physalaemin indicating the same receptor site as for BHSK. On the other hand, in rat cerebral cortex membranes BHE binding was inhibited by neuromedin K = kassinin = eledoisin greater than physalaemin greater than substance K greater than substance P indicating a definitive tachykinin E receptor site. The same displacement pattern of BHE binding was also detected in longitudinal muscle membranes from the guinea-pig small intestine. In mouse bladder membranes and in rat and guinea-pig intestine, the binding of BHSP was inhibited by substance P greater than physalaemin greater than substance K greater than or equal to eledoisin = kassinin greater than neuromedin K indicating a definitive tachykinin P receptor site. Autoradiographic binding sites for both BHSK and BHSP were seen in circular muscle of the rat stomach, small intestine and colon and in circular and longitudinal muscle of the guinea-pig small intestine and colon. Binding sites for BHSK, but not for BHSP, were seen in the muscularis mucosae of the gastric fundus and colon of the rat. Binding sites for BHSP, but not for BHSK, were seen in mucosa of guinea-pig colon and were densely clustered over ganglia of the myenteric and submucous plexuses in rat and guinea-pig colon. The guinea-pig intestine probably contains all three types of tachykinin binding sites whereas rat duodenum and mouse bladder contain only K and P sites. Some tissues classified previously as SP-P or SP-E may actually contain P and/or K sites.(ABSTRACT TRUNCATED AT 400 WORDS)