Autoradiographic localization and characterization of bradykinin receptors in human skin

High affinity [3H]bradykinin binding sites have been identified in human skin cryosections by in vitro autoradiography. Equilibrium binding studies were performed with increasing concentrations of [3H]bradykinin for 120 min in the presence of protease inhibitors at 4 degrees C. In saturation experiments a single class of high affinity binding sites was identified with a dissociation constant Kd of 1.2 +/- 0.8 nM (mean +/- S.E.M., n = 3) and a maximal binding capacity Bmax of 33 +/- 8 fmol [3H]bradykinin specifically bound/mg protein (mean +/- S.E.M., n = 3). Competition experiments revealed a rank order of potency with bradykinin being most effective (bradykinin = [Lys]bradykinin > [Met- Lys]bradykinin > [Tyr]bradykinin > [des-Arg9]bradykinin), whereas [des-Arg9]bradykinin was ineffective. This indicates a B2 subtype of bradykinin receptors in normal human skin. Morphological data: autoradiography revealed that bradykinin receptors were localized in the stratum basale of the epidermis. The data are consistent with the hypothesis, that these mitotic active keratinocytes express bradykinin binding 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 kinin receptors of the stratum basale are likely to contribute to these effects.