Unraveling the Disruptive Mechanism of Local Anesthetics on Raft-Like Ordered Membranes: Simulation Studies

The membrane perturbation of local anesthetics (LAs) with distinct steric differences─dibucaine (Dib), tetracaine (Tet), and lidocaine (Lid)─as well as their behavior in different regions of the raft-like ordered (Lo) membrane, were investigated using umbrella sampling molecular dynamics (MD) simulations. Both uncharged (-u) and protonated (-p) forms were considered. Our findings from potential mean force (PMF), z-axis diffusion, and area per lipid (APL) confirmed that Dib-u preferentially located at the hydrophobic core, whereas Lid-u shows no specific localization preference and exhibits rapid diffusion across the Lo membrane. The steric effect drives the distinct translocation behavior of LAs-u but has no significant impact on LAs-p. These two factors─bulky properties and high affinity for the hydrophobic core, as observed in Dib-u─contribute to the membrane disruption. This observation is evidenced by the significantly lower PMF profile at the deep hydrophobic core, the greatest lipid packing disorder, and high steric bulk, which is in reasonable agreement with experimental observations. Three-dimensional reference interaction-site model (3D-RISM) analysis further supports the amphiphilic nature of LAs-u and an increase in hydrophilicity of LAs-p. This difference is a key factor modulating the action of LAs-u and LAs-p forms in different membrane environments. Our findings on the distinct behavior governing the Lo membrane translocation of LAs-u are influenced by preferred localization within the Lo membrane and the steric effect. These insights offer valuable insights for the anesthetic design and membrane-based biosensor development.