Action of detergents on 3H-dihydroergokriptine binding and localization of alpha-adrenoceptors in synaptosomal membranes

3H-dihydroergokriptine (3H-DHE) binding was carried out in synaptosomal membranes from basal ganglia of the cat. A single type of binding site with Kd 3.7 nM, Hill number = 0.95 and Bmax = 1000 pmol/g protein was found. 3H-DHE bound to alpha-adrenoceptors and not to serotonin or dopamine receptors. At very low concentrations, some detergents enhanced binding, but at higher concentrations of those used (Triton X-100, Nonidet P-40, deoxycholate and digitonin), inhibited the binding of 3H-DHE. After binding to the membrane protein, the 3H-DHE-receptor complex was stable to the action of Triton X-100. At concentrations of Triton X-100. At concentrations of Triton X-100 (0.1--0.2%). in which only the presynaptic membrane disintegrated, the 3H-HDE specific radioactivity was reduced. With a more drastic treatment that disintegrated the postsynaptic membrane, 3H-DHE binding was further reduced. These results suggest that alpha-adrenergic receptors may be localized at both the pre- and postsynaptic membranes of central synapses.