Macromolecules from Lobster Axon Membranes That Bind Cholinergic Ligands and Local Anesthetics

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Abstract
The technique of reversible equilibrium dialysis has been applied to the study of macromolecules that are essential for axonal conduction. A binding component from a preparation of an axon-plasma membrane has been characterized and shown to bind nicotine with a K(D) = 0.42 +/- 0.04 muM and to the extent of 0.7 nmol/g of wet nerve. This binding was competitively blocked by acetylcholine (K(i) = 43 +/- 7 muM) and procaine (K(i) = 2.9 +/- 0.2 muM). This axonal macromolecule exhibits several of the properties of cholinergic postsynaptic receptors including its concentration in the tissue, blockade of its binding of nicotine by cholinergic drugs and alpha-bungarotoxin, and its phospholipoprotein nature. Some important differences are a lower affinity for acetylcholine and its binding of procaine. It is suggested that this nicotine receptor is on the internal surface of the axon plasma membrane and is a component common to both the Na(+) and K(+) gates.