Revisiting lipid - general anesthetic interactions (II): Halothane location and changes in lipid bilayer microenvironment monitored by fluorescence

A universal mechanism for the action of general anesthetics (GA) is not yet available. In this study, we investigated the interaction between halothane and 1,2-dipalmitoyl-sn-3-glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl-sn-3-glycero-3-phosphocholine (DOPC) bilayers labeled with Laurdan, Prodan, and NBD-C-6-PC as the reporter probes using steady-state fluorescence spectroscopy. We have evidence that halothane is located on the acyl chain side, near the headgroup region of the bilayer. Additionally, we find that halothane may be inhomogeneously distributed within DOPC and DPPC bilayers. We also show data that indicate halothane increases the free volume available to fluorescent probes. Differential scanning calorimetry and UV scanning calorimetry experiments were implemented to further observe the effects of halothane addition to the DPPC lipid bilayer. A significant shift of the phase-transition temperature of the DPPC system was observed. Our findings suggest that general anesthetic - lipid bilayer interactions may play a significant role in the overall mechanism of anesthetic action, and these effects should not be ignored when interactions between membrane proteins and anesthetics are considered.