Membrane structural perturbations caused by anesthetics and nonimmobilizers: A molecular dynamics investigation

The structural perturbations of the fully hydrated dimyristoyl-phosphatidyl choline bilayer induced by the presence of hexafluoroethane C-2F6, a "non i mmobilizer," have been examined by molecular dynamics simulations and compa red with the effects produced by halothane CF3CHBrCl, an "anesthetic," on a similar bilayer (DPPC) (Koubi et al., Biophys. J. 2000.78:800). We find th at the overall structure of the lipid bilayer and the zwitterionic head-gro up dipole orientation undergo only a slight modification compared with the pure lipid bilayer, with virtually no change in the potential across the in terface. This is in contrast to the anesthetic case in which the presence o f the molecule led to a large perturbation of the electrostatic potential a cross to the membrane interface. Similarly, the analysis of the structural and dynamical properties of the lipid core are unchanged in the presence of the nonimmobilizer although there is a substantial increase in the microsc opic viscosity for the system containing the anesthetic. These contrasting perturbations of the lipid membrane caused by those quite similarly sized m olecules may explain the difference in their physiological effects as anest hetics and nonimmobilizers, respectively.