AGONIST-INDUCED AFFINITY ALTERATIONS OF A CENTRAL NERVOUS-SYSTEM ALPHA-BUNGAROTOXIN RECEPTOR

Abstract— The ability of cholinergic agonists to block the specific interaction of α‐bungarotoxin (α‐Bgt) with membrane‐bound sites derived from rat brain is enhanced when membranes are preincubated with agonist. Thus, pretreatment of α‐Bgt receptors with agonist (but not antagonist) causes transformation of sites to a high‐affinity form toward agonist. This change in receptor state occurs with a half‐time on the order of minutes, and is fully reversible on dilution of agonist. The results are consistent with the identity of α‐Bgt binding sites as true central nicotinic acetylcholine receptors. Furthermore, this agonist‐induced alteration in receptor state may represent an in vitro correlate of physiological desensitization. As determined from the effects of agonist on toxin binding isotherms, and on the rate of toxin binding to specific sites, agonist inhibition of toxin binding to the high‐affinity state is non‐competitive. This result suggests that there may exist discrete toxin‐binding and agonist‐binding sites on central toxin receptors. Copyright © 1979, Wiley Blackwell. All rights reserved