Presence and subcellular localization of alpha 2-adrenoceptors in dog splenic nerve.

Two weeks after denervation of the dog spleen, alpha 2-adrenoceptors labelled by [3H]rauwolscine were decreased to 44% of control. In splenic nerve, high-affinity, specific, stereoselective [3H]rauwolscine binding was observed, with a Bmax of 211 +/- 49.8 fmol/mg protein and a Kd of 4.33 +/- 0.87 nM. The [3H]rauwolscine binding sites in the splenic nerve were not co-localized with noradrenaline (NA) in the NA-storage vesicles, as revealed by sucrose density gradients. Moreover, unlike NA and its storage vesicles, no accumulation of alpha 2-adrenoceptors against a ligature could be observed. The results demonstrate the presence of alpha 2-receptors in the splenic nerve, and their localization in the axon, distinct from the large dense-cored vesicles.