[3H]rauwolscine (α-yohimbine): A specific antagonist radioligand for brain α2-adrenergic receptors

Abstract

[³H]Rauwolscine, a specific and potent α₂-antagonist radioligand, was used to characterize α₂-receptor binding in bovine cerebral cortex [³H]Rauwolscine binding was reversible, stereospecific, and saturable. Association, dissociation, and saturation studies revealed one site interactions ($\text{k}{}_{\mathrm{-1}}\text{k}{}_{\mathrm{+1}}\text{= 1.2}\text{nM}\text{,}\text{K}{}_{\mathrm{<mtext>D</mtext>}}\text{= 2.5}\text{nM}\text{,}\text{B}{}_{\mathrm{<mtext>max</mtext>}}\text{= 160}\text{fmol}\text{mg}$ protein) and competition studies indicated that [³H]rauwolscine labeled the α₂-receptor. Agonists inhibited [³H]rauwolscine binding in a shallow, GTP-sensitive manner. These results suggest that [³H]rauwolscine specifically labels both the high and low affinity states of the α₂-receptor in brain membranes.