McQuarrie_1976_J.Biol.Chem_251_6335

Binding of alpha-bungarotoxin, labeled with 125I, has been studied in crude membrane preparations of rat cerebral cortex. Membrane-bound receptors appear to consist of at least two saturable subsets: one accounts for the binding of about 50 fmol of toxin/mg of protein, the other binds 120 fmol/mg. For the high affinity sites the dissociation constant for interaction of toxin and receptor extrapolated to zero protein concentration is 9.2 X 10(-10) M. Competition with a variety of agonists and antagonists indicates that toxin binding exhibits the pattern expected for nicotinic acetylcholine receptors. Toxin binding is inhibited by low concentrations of Ca2+ ions (50% inhibition at 3 mM) while higher concentrations are required for Mg2+, Na+, K+, and Li+ (50% inhibition at 0.5 M).