title: Sodium-dependent high-affinity binding of [3H]hemicholinium-3 in the rat brain: a potentially selective marker for presynaptic cholinergic sites.
abstract: This report describes the membrane binding properties of [3H]hemicholinium-3 ([3H]HC-3), a selective inhibitor of sodium-dependent high-affinity choline uptake (SDHACU) in cholinergic nerve terminals. Under the described assay conditions, [3H]HC-3 bind with a saturable population of high-affinity (apparent Kd = 1.9 nM) CNS membrane sites having the regional distribution: striatum much greater than hippocampus greater than cerebral cortex greater than cerebellum. High-affinity [3H]HC-3 binding is entirely dependent upon the presence of sodium chloride (EC50 = 35-50 mM) and is markedly reduced when other salts of sodium or monovalent ions are substituted. [3H]HC-3 binding is inhibited by choline (Ki = 6 microM) and acetylcholine (Ki = 35 microM) but markedly less sensitive to other cholinergic agents and metabolic inhibitors. In light of the similar ionic dependencies, regional distributions and pharmacological specificities of [3H]HC-3 binding and SDHACU, closely associated sites may be involved in both processes.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002794:Choline / Q000494:pharmacology; D006426:Hemicholinium 3 / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011950:Receptors, Cholinergic / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology*; D013569:Synapses / Q000502:physiology*; D014018:Tissue Distribution
chemical_list: D011950:Receptors, Cholinergic; D006426:Hemicholinium 3; D012965:Sodium Chloride; D002794:Choline; D000109:Acetylcholine