Structural-functional correlates of the nicotinic acetylcholine receptor and its lipid microenvironment

Among the proteins specialized in signal transduction, the nicotinic acetylcholine receptor (AChR) is the best-characterized member of the superfamily of ligand-gated ion channels. Since the early finding of a motionally restricted shell of lipids (annulus) encircling the protein in its native membrane, there is growing experimental evidence supporting the notion that this interface region is the locus of a variety of pharmacologically relevant processes, including some of the actions of local anesthetics, steroids, and other lipophilic compounds. Biochemical data on the composition and metabolism of AChR-rich membranes and cells, combined with biophysical data on their structure and dynamics, are beginning to provide information on the nature of the annulus itself. Patch-clamp data on cells expressing the AChR protein add another dimension to this knowledge, enabling correlations to be established between the chemical composition of lipid-modified cells and the functional properties of the receptor protein in situ at the single-channel level. The effect of free fatty acids, alcohols, phospholipids, cholesterol, and steroid glucocorticoid hormones on the function of the AChR is reviewed. In the case of steroids, their effects at the single-channel level bear a relationship to their use in pathological conditions of medical relevance, e.g., in the treatment of the disease myasthenia gravis.