A structure-based approach to nicotinic receptor pharmacology

Infrared difference spectroscopy has been used to examine the structural effects of local anesthetic (LA) binding to the nicotinic acetylcholine receptor (nAChR). Several LAs induce subtle changes in the vibrational spectrum of the nAChR over a range of concentrations consistent with their reported nAChR-binding affinities. At concentrations of the desensitizing LAs prilocaine and lidocaine consistent with their binding to the ion channel pore, the vibrational changes suggest the stabilization of an intermediate conformation that shares structural features in common with both the resting and desensitized states. Higher concentrations of prilocaine and lidocaine, as well as the LA dibucaine, lead to additional binding to the neurotransmitter-binding site, the formation of physical interactions (most notably cation-tyrosine interactions) between LAs and neurotransmitter-binding-site residues, and the subsequent formation of a presumed desensitized nAChR. Although concentrations of the LA tetracaine consistent with binding to the ion channel pore elicit a reversed pattern of spectral changes suggestive of a resting state-like nAChR, higher concentrations also lead to neurotransmitter site binding and desensitization. Our results suggest that LAs stabilize multiple conformations of the nAChR by binding to at least two conformationally sensitive LA-binding sites. The spectra also reveal subtle differences in the strengths of the physical interactions that occur between LAs and binding-site residues. These differences correlate with LA potency at the nAChR.