CHARACTERIZATION AND AUTORADIOGRAPHIC MAPPING OF [H-3] CP96,345, A NONPEPTIDE SELECTIVE NK1 RECEPTOR ANTAGONIST IN GUINEA-PIG LUNG

We have studied binding and distribution of NK1 receptors in guinea pi g lung using [H-3]CP96,345. Kinetic studies showed that specific bindi ng of [H-3]CP96,345 was rapid and reversible, giving a kinetic dissoci ation constant (K-d) of 0.28 +/- 0.05 nM. The specific binding was als o saturable and Scatchard analysis indicated a single class of binding site with an equilibrium K-d of 0.12 +/- 0.03 nM and maximum binding capacity (B-max) of 107.0 +/- 10.3 fmol/mg of protein. Competition stu dies showed the rank order of affinity for agonists and antagonists as follows: SP > NKA = septide much greater than NKB = senktide; CP96,34 5 > FK888 > FK224 > L668169. NK3 agonists, NK2-selective antagonists, and a calcium channel blocker, diltiazem, showed no displacement, indi cating high selectivity for NK1 receptors. Autoradiographic mapping sh owed specific labeling over airway smooth muscle from central to perip heral airways, submucosal glands, and nerve fibers of trachea. The lab eling of airway epithelium was increased with diminishing size of airw ays. Pulmonary blood vessels were also moderately labeled and there wa s sparse labeling over alveolar walls. [H-3]CP96,345 may provide a use ful tool to evaluate NK1 receptor expression in peripheral organs.