DISTRIBUTION OF GENERAL-ANESTHETICS IN PHOSPHOLIPID-BILAYERS DETERMINED USING H-2 NMR AND H-1-H-1 NOE SPECTROSCOPY

The effect of the general anesthetics halothane, enflurane, and isoflu rane on hydrocarbon chain packing in palmitoyl(d(31))oleoylphosphatidy lcholine membranes in the liquid crystalline phase was investigated us ing H-2 NMR. Upon the addition of the anesthetics, the first five meth ylene units near the interface generally show a very small increase in segmental order, while segments deeper within the bilayer show a smal l decrease in segmental order. From the H-2 NMR results, the chain len gth for the perdeuterated palmitoyl chain in the absence of anesthetic was found to be 12.35 Angstrom. Upon the addition of halothane enflur ane, or isoflurane, the acyl chain undergoes slight contractions of 0. 11, 0.20, or 0.16 Angstrom, respectively, at 50 mol % anesthetic. A si mple model was used to estimate the relative amounts of anesthetic loc ated near the interface and deeper in the bilayer hydrocarbon region, and only a slight preference for an interfacial location was observed. Intermolecular H-1-H-1 nuclear Overhauser effects (NOEs) were measure d between phospholipid and halothane protons. These NOEs are consisten t with the intramembrane location of the anesthetics suggested by the H-2 NMR data. In addition, the NOE data indicate that anesthetics pref er the interfacial and hydrocarbon regions of the membrane and are not found in high concentrations in the phospholipid headgroup.