Studies of nicotinic acetylcholine receptor protein from rat brain.

Specific binding of 125I-labeled alpha-bungarotoxin to a 34800 X g pellet of a whole rat brain homogenate has been obtained at levels of 2 pmol toxin per g of whole brain with a Kd of 8-10(-9) M. Binding is reduced 90% by 10(-5) M (+)-tubocurarine chloride and 10(-4) M nicotine, whereas concentrations of 10(-4) M choline chloride, atropine sulfate and eserine sulfate have essentially no effect on toxin binding. These results compare closely with those obtained from binding studies with 125I-labeled alpha-bungarotoxin and soluble acetylcholine receptor protein preparations from Torpedo nobiliana; suggesting that this mammalian receptor protein is nicotinic in character. Extraction of the 34800 X g pellet with 1% Emulphogene yields a soluble fraction with specifically binds 125I-labeled alpha-bungarotoxin with a Kd of 5-10(-9) M. Nicotine and alpha-bungarotoxin at concentrations of 10(-5) M abolish toxin-receptor complex formation and carbachol and (+)-tubocurarine chloride reduce complex formation 35-40% at similar concentrations. Eserine sulfate, atropine sulfate, decamethonium, and pilocarpine had no effect on complex formation at concentrations of 10(-5) M.