AUTORADIOGRAPHIC LOCALIZATION AND CHARACTERIZATION OF BRADYKININ RECEPTORS IN HUMAN SKIN

High affinity [H-3]bradykinin binding sites have been identified in hu man skin cryosections by in vitro autoradiography. Equilibrium binding studies were performed with increasing concentrations of [H-3]bradyki nin for 120 min in the presence of protease inhibitors at 4 degrees C. In saturation experiments a single class of high affinity binding sit es was identified with a dissociation constant K-d of 1.2 +/- 0.8 nM ( mean +/- S.E.M., n = 3) and a maximal binding capacity B-max of 33 +/- 8 fmol [H-3]bradykinin specifically bound/mg protein (mean +/- S.E.M. , n = 3). Competition experiments revealed a rank order of potency wit h bradykinin being most effective (bradykinin = [Lys]bradykinin > [Met -Lys]bradykinin > [Tyr]bradykinin > [des-Arg(9)]bradykinin), whereas [ des-Arg(9)]bradykinin was ineffective. This indicates a B-2 subtype of bradykinin receptors in normal human skin. Morphological data: autora diography revealed that bradykinin receptors were localized in the str atum basale of the epidermis. The data are consistent with the hypothe sis, that these mitotic active keratinocytes express bradykinin bindin g sites, that fulfil the pharmacological criteria for true receptors. Diverse stimuli, including bradykinin, play a role in the mediation of cutaneous inflammatory responses (e.g. fluid extravasation, reactive cell proliferation, hyperalgesia). Our data indicate that specific kin in receptors of the stratum basale are likely to contribute to these e ffects.