Conversion between configurational states of the muscarinic receptor in rat brain.

Reductive alkylation of neural membranes by N-ethyl maleimide (NEM) converts muscarinic acetylcholine receptors from a state of low to high affinity for receptor agonists. Interactions of muscarinic antagonists with the receptor are unaffected by this treatment. Muscarinic receptors from the rat telencephalon in the high agonist affinity state are increased from 34.2 to 53.4% of the total receptor population and the Ki for carbamylcholine inhibition of 3-quinuclidinyl benzilate binding is decreased from 1.2 X 10(-4) to 6.9 X 10(-5) M by NEM treatment.