Identification of an imidazoline-guanidinium receptive site in mitochondria from rabbit cerebral cortex

In the present report, we used [3H]idazoxan to characterize imidazoline-guanidinium receptive sites (IGRS) in mitochondria from rabbit cerebral cortex. When compared to the starting homogenate, [3H]idazoxan binding was higher (1.161 +/- 0.159 vs. 0.102 +/- 0.024 pmol/mg of protein) in a membrane fraction 6-fold enriched in cytochrome oxidase activity, a specific marker for mitochondria. In addition, the enrichment of [3H]idazoxan binding sites positively correlates with cytochrome oxidase activity in different membrane preparations (r = 0.977, P less than 0.001). In competition studies, [3H]idazoxan binding was completely inhibited by imidazoline and guanidinium derivatives but not affected by 10 microM epinephrine. Taken together, these data show the localization of IGRS in the mitochondria from rabbit cerebral cortex.