AHN 086: an irreversible ligand of "peripheral" benzodiazepine receptors

AHN 086, a derivative of 4'-chlorodiazepam (Ro 5-4864) containing an isothiocyanate moiety, binds irreversibly to "peripheral" benzodiazepine receptors in the kidney with an IC50 of approximately 1.3 nM. Using standard incubation conditions (50 mM potassium phosphate buffer, pH 7.0, 0 degrees), AHN 086 reacted rapidly with "peripheral" benzodiazepine receptors, whereas a time-dependent inhibition of [3H]Ro 5-4864 binding by AHN 086 could be demonstrated by decreasing the pH of the reaction mixture, suggesting the presence of a histidine residue at or near the locus at which AHN 086 reacts. At concentrations up to 1 microM, AHN 086 did not inhibit [3H]flunitrazepam binding to "central-type" benzodiazepine receptors. Thus, AHN 086 appears to be a specific, high affinity, irreversible ligand of "peripheral" benzodiazepine receptors.