HETEROGENEITY OF NEUROKININ, BINDING-SITES IN PORCINE RESPIRATORY-TRACT

High-affinity NK, binding sites for [(125)]BH-SP were characterized in adult porcine respiratory tract. The affinity and density of NK1 site s were significantly higher in tracheal epithelium and smooth muscle t han in the lung. The potency order for agonists was: SP > neuropeptide -gamma > physalaemin > NKA > eledoisin > septide > SP methyl ester > G R 73632 > NKB > senktide > SP(1-7). For antagonists: CP 99,994 > CP 96 ,345 > spantide > L 703,606 much greater than WIN 51,708. The CP compo unds discriminated between very high- and high-affinity NK1 sites in a ll three tissues. The subpopulation of sites with very high affinity f or CP compounds also preferentially bound septide. Both binding compon ents were inhibited by guanine nucleotide and showed equal affinities for SP. We propose an NK1B subtype with very high affinity for the ant agonists CP 99,994 and CP 96,345 and the agonist septide, and an NK1A subtype with lower affinities for these ligands.