Interactions between volatile anesthetics and dipalmitoyl phosphatidylcholine liposomes as studied by fluorometry with a thiacarbocyanine dye

Isoflurane strongly affects the diffusion of intracellular metabolites, as shown by 1H nuclear magnetic resonance spectroscopy of the monkey brain

Isoflurane is a volatile anesthetic commonly used for animal studies. In particular, diffusion nuclear magnetic resonance (NMR) spectroscopy is frequently performed under isoflurane anesthesia. However, isoflurane is known to affect the phase transition of lipid bilayer, possibly resulting in increased permeability to metabolites. Resulting decreased restriction may affect metabolite apparent diffusion coefficient (ADC). In the present work, the effect of isoflurane dose on metabolite ADC is evaluated using diffusion tensor spectroscopy in the monkey brain. For the five detected intracellular metabolites, the ADC exhibits a significant increase when isoflurane dose varies from 1% to 2%: 13%+/-8% for myo-inositol, 14%+/-13% for total N-acetyl-aspartate, 20%+/-18% for glutamate, 27%+/-7% for total creatine and 53%+/-17% for total choline. Detailed analysis of ADC changes experienced by the five different metabolites argues in favor of facilitated metabolite exchange between subcellular structures at high isoflurane dose. This work strongly supports the idea of metabolite diffusion in vivo being significantly restricted in subcellular structures at long diffusion time, and provides new insights for interpreting ADC values as measured by diffusion NMR spectroscopy.

Effects of high pressure on polarity change of the water-liposome interface induced by volatile anesthetics

The effects of high pressure on the interactions between volatile anesthetics and three kinds of phosphatidyl choline liposomes were investigated by fluorometry, using a thiacarbocyanine dye (3,3"-dioctadecyl-2,2"-thiacarbocyanine) which is sensitive to the environmental viscosity and dielectric constant. Seven general anesthetics, halothane, enflurane, isoflurane, methoxyflurane, sevoflurane, diethylether and chloroform were used. We have previously reported that these anesthetics decreased the phase transition temperature and increased the effective dielectric constant of the water-liposome interface using dipalmitoyl-phosphatidylcholine. In this study, it was confirmed that the effects of anesthetics on the effective dielectric constant were not altered by the use of a gel or liquidcrystal membrane, and were reversed by the application of high pressure (<800 bars). The increase of the effective dielectric constant was attributed to the perturbation of hydrogen bonds at the liposomal interface. High pressure is considered to promote hydration. Our results obtained under high pressure supported previous observations made at ambient pressure, which suggested that the perturbation of hydrogen bonds at the water-liposome interface correlates with the mechanism of anesthesia.