Characterization of [H-3]substance P binding sites in human skin

Radioligand binding experiments were performed with crude homogenates from normal human skin in order to investigate substance P receptor density. Bin ding of [H-3]substance P ([H-3]SP) reached equilibrium after 20 min and was saturable; analysis of saturation curves gave a significantly better fit u sing two-site binding compared to the single-site model. Competition studie s employing some selective agonists for NK1, NK2 and NK3 receptors have dem onstrated that only the NK1 selective agonist, [Sar(9), Met(O-2)(11)]-SP, w as a competitor for [H-3]SP binding. In addition, the non-hydrolyzable guan osine 5'-0-(3-thiotriphosphate) altered the dissociation of SP from NK1 rec eptors by increasing the number of low-affinity sites. These data show that in the skin [H-3]SP binds to a single population of substance P high-affin ity sites, which represent NK1-type receptors. (C) 1999 Elsevier Science B. V. All rights reserved.