Light microscopic autoradiography of the distribution of [3H]rauwolscine binding to α2-adrenoceptors in rat kidney

The localization of [³H]rauwolscine binding to microscope slide mounted sections of rat kidney has been examined using the technique of in vitro labelling and autoradiography. Binding to sections equilibrated within 60 min and was reversible following the addition of 10 μM phentolamine. Saturation studies revealed a single population of high affinity (K_D 4.27 nM) non-interacting sites (nH 0.97) with a density of 11.1 fmol/section. Stereoselectivity was observed with respect to the isomers of noradrenaline and the relative affinity of a series of α-adrenoceptor antagonists suggested binding to α₂-adrenoceptors. Autoradiographic studies using ³H-Ultrofilm showed that the binding is largely confined to the renal cortex. More detailed studies using emulsion coated coverslips indicates that the major concentration of binding sites is over the proximal tubules. This study provides evidence that α₂-adrenoceptors, known to be coupled in an inhibitory fashion to renal adenylate cyclase, are highly localized to particular structures in the kidney.