Single-Molecule and Super-Resolution Diffusion Quantification Unveils Reversible Enhancement of Lipid-Membrane Diffusivity by General Anesthetics

The molecular mechanism of general anesthesia remains a mystery. While many small molecules, ranging from xenon to diethyl ether, act as general anesthetics, few similarities exist in their chemical structures or properties. Utilizing single-molecule displacement/diffusivity mapping (SM<i>d</i>M), a diffusion-quantifying single-molecule and super-resolution microscopy tool, we unveil that at clinical concentrations, general anesthetics rapidly and reversibly enhance the lateral diffusivity of both model lipid bilayers and live-cell plasma membranes in a dose-dependent fashion based on the anesthetic potency. With <i>in situ</i> fluorescence microscopy, we next show that the partitioning of anesthetics into the lipid bilayer causes fast dilation and area expansion. Employing a liposome-based fluorescence quenching assay, we further unveil enhanced lipid-bilayer permeability to the chloride ion (Cl^-) in an anesthetic-concentration-dependent fashion. Together, our results indicate that the reversible insertion of anesthetic molecules into the lipid bilayer enhances the diffusivity and permeability of the lipid membrane, thus compromising neural functions.