The neuronal nicotinic acetylcholine receptors are likely to be oligomeric proteins composed of five subunits. If these receptors were all homo-oligomers, there might be one unique receptor that corresponded to each pentameric arrangement of each of the available subunits. The situation is more complicated than that because most of the neuronal nicotinic receptors are hetero-oligomers. These hetero-oligomeric receptors contain both alpha and beta subunits. Because individual alpha subunits can participate in the formation of functional receptors with more than one kind of beta subunit, the number of possible receptors is larger. This chapter documents several examples of the functional heterogeneity of the neuronal nicotinic receptors and presents new properties that characterize these receptors. Specifically, it reviews data showing the pharmacological diversity of neuronal nicotinic acetylcholine receptors and shows that these receptors differ from the muscle nicotinic acetylcholine receptors in their permeability to calcium and in their modulation by external calcium ions.
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