Insights into Distinct Modulation of α7 and α7β2 Nicotinic Acetylcholine Receptors by the Volatile Anesthetic Isoflurane

Background: What determines hypersensitivity or insensitivity of 2-containing or 7 nAChRs to volatile anesthetics remains unclear. Results: Isoflurane binds to the EC end of the TM domain, modulates channel dynamics, and inhibits channel current in 2 not 7. Conclusion: The dynamic and structural differences between 2 and 7 affect isoflurane binding and inhibition. Significance: Both structure and dynamics are critical for drug action. Nicotinic acetylcholine receptors (nAChRs) are targets of general anesthetics, but functional sensitivity to anesthetic inhibition varies dramatically among different subtypes of nAChRs. Potential causes underlying different functional responses to anesthetics remain elusive. Here we show that in contrast to the 7 nAChR, the 72 nAChR is highly susceptible to inhibition by the volatile anesthetic isoflurane in electrophysiology measurements. Isoflurane-binding sites in 2 and 7 were found at the extracellular and intracellular end of their respective transmembrane domains using NMR. Functional relevance of the identified 2 site was validated via point mutations and subsequent functional measurements. Consistent with their functional responses to isoflurane, 2 but not 7 showed pronounced dynamics changes, particularly for the channel gate residue Leu-249(9). These results suggest that anesthetic binding alone is not sufficient to generate functional impact; only those sites that can modulate channel dynamics upon anesthetic binding will produce functional effects.