Receptor binding experimental approaches

Inhaled nicotine is efficiently delivered to the brain (see chapter by Benowitz, this volume) where it selectively interacts with its central targets, the neuronal nicotinic acetylcholine receptors (nAChRs). The multiple subtypes of uAChR (see chapter by Collins et al, this volume) all bind nicotine but with different affinities, depending on the subunit composition of the uAChR. Binding may result in activation or desensitisation of uAChRs, reflecting the temporal characteristics of nicotine dehvery and local concentration of nicotine. Another level of complexity of the actions of nicotine reflects the widespread and non-uniform distribution of uAChR subtypes within the brain, such that nicotine can influence many centrally regulated functions in addition to the reward systems. In this chapter, we address the consequences of nicotine interactions with nAChRs at the molecular, cellular and anatomical levels. We critically evaluate experimental approaches, with respect to their relevance to human smoking, and contrast the acute and chronic effects of nicotine. 

In addition to the C-terminus, several other regions of Ga have been implicated in receptor binding by a variety of experimental approaches (Fig. 4). Residues in the a4//16 loop contribute to the binding surface as demonstrated by alanine-scanning mutagenesis (Onrust et al, 1997), studies with chimeric Ga proteins (Bae et al., 1997, 1999), sequence analysis of conserved amino acids in Ga subclasses (Lichtarge et al., 1996), chemical cross-linking (Cai et al, 2001), and protection from tryptic proteolysis (Mazzoni and Hamm, 1996). The C-terminal 11 amino acids of Gat and... 

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