Properties of [³H]bunazosin binding in rat kidney

Properties of alpha₁-adrenoceptor binding in the renal cortex of rats were studied with [³H]bunazosin as the radiolabeled ligand. Both temperature and incubation time influened bunazosin receptor binding. Subcellular distribution of [³H]bunazosin binding revealed that the membrane fraction (30,000 x g pellet) had the largest proportion of total binding sites. Pretreatment of membrane preparation at 56°C for 30 minutes greatly decreased the specific binding of [³H]bunazosin, though there was no significant effect of the pretreatment at 24°C and 37°C for 30 minutes. Among various cations, some divalent ions such as Cu⁺⁺ and Zn⁺⁺ greatly decreased bunazosin binding, whereas monovalent ions had no effect on specific binding. Results of Scatchard analysis suggested that the rat renal cortex membrane has single binding sites with an apparent dissociation constant of 0.38 ± 0.06 nmol/L, though the rat medulla membrane has no potent binding activity with bunazosin. The displacement study revealed that various adrenergic agents inhibit [³H]bunazosin binding in dose-dependent fashion; the rank order of potencies was bunazosin prazosin > phentolamine >> dl-norepinephrine > clonidine, yohimbine >> pindolol, propranolol. These findings reveal that bunazosin has specific receptor binding in the rat renal cortex, indicating that alpha₁-adrenoceptors exist in the rat renal cortex.