Anesthetic Concentrations of Halothane Change the Domain Structure of Mixed Lipid Membranes

Abstract

Binary and ternary mixtures of lipids that form separate phases (gel, fluid-ordered, and fluid disordered) may provide useful insights into the complex physics of real biological membranes. Here, we examine the mixing versus temperature of DPPC:DLPC and DPPC:DOPC:Cholesterol phase separated systems using neutron and x-ray diffraction methods. We also report the affects of inhalation anesthetics on the phase behavior of these lipid mixtures. Phase co-existence was measured by lamellar x-ray diffraction from multi-layer samples. Two distinct series of lamellar Bragg diffraction were observed demonstrating separation into distinct 3D phases. We observe a broad transition in which one phase diminishes as a function of temperature resulting in a single homogenous phase. We used isotopic contrast from chain deuterated lipids to show compositional changes in the fluid phase during the mixing transition. The changes seen in the proportion of lipids in the lamellar diffraction studies correspond to physical mixing of the lipid species shown by examining the chain diffraction at wide angles produced by deuterated lipids. Finally, we show that the anesthetic halothane shifts the temperature mixing curves and sharpens the transition of these mixtures.