Detection of low-affinity alpha-bungarotoxin binding sites in the rat central nervous system

The curaremimetic neurotoxin, alpha-bungarotoxin, is shown to interact with two classes of binding sites on rat brain crude mitochondrial fraction membranes. Toxin binding sites are characterized by descriptive, preequilibrium dissociation constants of about 5 and 400 nM. There are at least as many low-affinity toxin binding sites as high-affinity sites. The existence of low- and high-affinity sites is confirmed by experiments with native toxin. Low- and high-affinity toxin binding sites are copurified as judged by sedimentation velocity and density gradient analysis, consistent with the presence of low- and high-affinity toxin binding sites on the same subcellular membrane fragments. The results may offer an explanation for the relatively low antagonistic potency of curaremimetic neurotoxins at acetylcholine-sensitive sites in the vertebrate central nervous system.