title: alpha-Bungarotoxin binds to low-affinity nicotine binding sites in rat brain.
abstract: Reported differences in the pharmacology and distribution of [3H]nicotine and [125I]alpha-bungarotoxin binding sites in mammalian brain suggest that these ligands label separate receptor sites. Affinity purification of an alpha-bungarotoxin binding protein from rat brain failed to copurify the high-affinity nicotine binding site, which remained in the nonbound soluble fraction after the affinity chromatography step. This confirms the independence of these putative receptor sites. Nevertheless, the binding of [125I]alpha-bungarotoxin to P2 membranes was inhibited by (-)-nicotine (Ki = 9 X 10(-6) M), and this sensitivity was preserved after affinity purification. It is proposed that alpha-bungarotoxin binds to a population of low-affinity nicotine binding sites. Comparison of the enantiomers of nicotine in competition studies at both radioligand binding sites revealed an 80-fold preference for the (-) form at the high-affinity [3H]nicotine binding site, whereas the site labelled by [125I]alpha-bungarotoxin displayed little stereoselectivity. In this respect, the brain alpha-bungarotoxin binding site resembles the nicotinic acetylcholine receptor from Torpedo electric organ.
mesh_terms: D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D002038:Bungarotoxins / Q000378:metabolism*; D008297:Male; D009538:Nicotine / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011978:Receptors, Nicotinic / Q000378:metabolism*; D013570:Synaptic Membranes / Q000378:metabolism; D014101:Torpedo
chemical_list: D002038:Bungarotoxins; D011978:Receptors, Nicotinic; D009538:Nicotine