Nicotinic receptor pore mutations create a sensitive inhibitory site for ethanol

Area of Science:

• Neuroscience
• Pharmacology
• Molecular Biology

Background:

• Ethanol (EtOH) affects ligand-gated ion channels, but its precise interaction sites and mechanisms remain unclear.
• Peripheral nicotinic receptors exhibit low sensitivity to EtOH, suggesting specific structural requirements for inhibition.
• This study investigates whether mutations in the nicotinic receptor pore can confer sensitivity to physiological EtOH concentrations.

Purpose of the Study:

• To determine if increasing hydrophobicity and/or size of nicotinic receptor pore sites can lead to EtOH inhibition at physiological concentrations.
• To elucidate the roles of residue size versus hydrophobicity in determining EtOH sensitivity at the alpha252 position.

Main Methods:

• Utilized patch-clamp electrophysiology to study recombinant mouse muscle nicotinic receptors.
• Measured EtOH effects on single-channel conductance and multichannel currents.
• Investigated pairs of mutants with similar residue sizes but differing hydrophobicity at alpha252.

Main Results:

• Wild-type receptors are inhibited by EtOH only at concentrations >300 mM.
• Mutations alphaS252I and betaT263I significantly increase EtOH sensitivity, with 50 mM EtOH inhibiting mutated receptors.
• Hydrophobic side-chain alterations at alpha252, not size, were found to be critical for enhanced EtOH sensitivity.
• EtOH inhibition correlates with reduced open-state conductance of single nicotinic channels.

Conclusions:

• Nicotinic receptors possess low EtOH affinity, but pore mutations can confer sensitivity to physiological EtOH levels.
• Ethanol inhibition primarily involves interactions with the open state of the channel.
• Side-chain hydrophobicity at alpha252 is the key determinant of EtOH sensitivity, not residue size.
• Similar EtOH-sensitive sites may exist in other ion channels like NMDA and neuronal nicotinic receptors.