Action of detergents and pre- and postsynaptic localization of 3H-naloxone binding in synaptosomal membranes. A structural approach.

3H-naloxone specific binding was carried out on synaptosomal membranes isolated from basal ganglia of the cat brain. A high- and a low-affinity site with Kd1 = 3.7 nM and Kd2 = 35 nM having B max 1 = 79 pmole/g protein and B max 2 = 224 pmole/g protein were found. The Hill number for the high- and low-affinity sites were, respectively, 1.01 and 0.86. Digitonin and Triton X-100 had an inhibitory effect on the binding at concentrations between 10(-5) and 10(-1)% (w/v). Deoxycholate and Nonidet P-40 also inhibited the binding of 3H-naloxone, but at 10(-4)% produced a 50% enhancement. After the binding to membranes, the 3H-naloxone receptor complex is stable to the action of Triton X-100 and dissociates slowly. In membranes bound with 10 nM 3H-naloxone and then submitted to 0.1-0.2% Triton X-100, in which only the presynaptic membrane disintegrates, the specific radioactivity is decreased. With a more drastic treatment that disintegrates the postsynaptic membrane, the 3H-naloxone binding to synaptosomal membranes is almost completely abolished. These results suggest that opiate receptors may be localized both pre- and postsynaptically in central synapses.