BINDING OF [H-3] CIRAZOLINE TO AN IMIDAZOLINE SITE IN RAT-BRAIN AND KIDNEY MEMBRANES

Two classes of high-affinity sites for [H-3]cirazoline were characteri zed in rat brain and kidney membranes. In both tissues, the binding pa rameters for the high- and low-affinity sites are similar with B-max v alues of similar to 50 fmol/mg protein, K-d similar to 0.6 nM and B(ma x)similar to 470 fmol/mg protein, K-d similar to 11 nM respectively. I nhibition studies of [H-3]cirazoline binding to the lower affinity sit e revealed that only guanidinium or imidazoline derivatives compete wi th the specific binding of this radioligand. Our results suggest that [H-3]cirazoline could be used as a novel ligand to label the non-adren ergic imidazoline-preferring sites.