IDENTIFICATION OF AN IMIDAZOLINE-GUANIDINIUM RECEPTIVE SITE IN MITOCHONDRIA FROM RABBIT CEREBRAL-CORTEX

In the present report, we used [H-3]idazoxan to characterize imidazoline-guanidinium receptive sites (IGRS) in mitochondria from rabbit cerebral cortex. When compared to the starting homogenate, [H-3]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 [H-3]idazoxan binding sites positively correlates with cytochrome oxidase activity in different membrane preparations (r = 0.977, P < 0.001). In competition studies, [H-3]idazoxan binding was completely inhibited by imidazoline and granidinium derivatives but not affected by 10-mu-M epinephrine. Taken together, these data show the localization of IGRS in the mitochondria from rabbit cerebral cortex.