[H-3] MAZINDOL BINDING ASSOCIATED WITH NEURONAL DOPAMINE AND NOREPINEPHRINE UPTAKE SITES

Abstract

[3H]Mazindol labels neuronal dopamine uptake sites in corpus striatum membranes (Kd = 18 nM) and neuronal norepinephrine uptake sites in cerebral cortex and submaxillary/sublingual gland membranes (Kd = 4 nM). Potencies of various inhibitors of biogenic amine uptake in reducing [3H]mazindol binding in striatal membranes correlate with their potencies for inhibition of neuronal [3H]dopamine accumulation; their potencies in reducing [3H]mazindol binding to cortical and salivary gland membranes correlate with their potencies for inhibition of neuronal [3H]norepinephrine accumulation. Similar to the dopamine and norepinephrine uptake systems, [3H]mazindol binding in all 3 tissues is dependent upon Na (with K, Li, Rb and Tris being ineffective substitutes) and Cl (with SO42- and Pi being ineffective substitutes). In membranes of the cerebral cortex and salivary gland, half-maximal stimulation is observed at 50-80 mM NaCl; in membranes of the corpus striatum half-maximal stimulation occurs at 240 mM NaCl. In striatal membranes NaCl increases the affinity of [3H]mazindol binding with no effect on the maximal number of sites. Enhancement of affinity is due to a selective slowing of the dissociation of the ligand from its binding site. Association of [3H]mazindol binding sites with neuronal dopamine uptake sites in the corpus striatum is further supported by the reduction of [3H]mazindol binding sites in striatal membranes following destruction of dopaminergic neurons by 6-hydroxydopamine. Association of [3H]mazindol binding sites with neuronal norepinephrine uptake sites in cerebral cortex is supported by the reduction of [3H]mazindol binding to cortical membranes following destruction of noradrenergic neurons by N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine.