The effects of volatile anesthetics on the binding of 1-anilino-8-naphthalene sulphonate to biological membranes and lipid vesicles: the role of cholesterol.

The effects of volatile anesthetics on the properties of membrane surfaces were studied using the negatively charged fluorescent probe 1-anilino-8-naphthalene sulphonate (ANS). Although the addition of the anesthetics caused no change of the fluorescence quantum yield of ANS bound to the biological membranes, there was a significant increase of the number of binding sites (n) for ANS to the membranes. This increase was also found after treating the membranes with either trypsin or neuraminidase and with vesicles of total lipids extracted from erythrocytes. With phosphatidylcholine (PC) vesicles, the fluorescence increase by the addition of anesthetics was observed only when the vesicle contained cholesterol. The greater increase of the n value was seen in vesicles containing a higher concentration of cholesterol. When the neutral probe, N-phenyl-1-naphthylamine (NPN) was used instead of ANS, this fluorescence increase was not seen. These results were interpreted in terms of the electrostatical change of the membrane lipid region. That is, a change of the surface potential of the membrane is possibly caused by the anesthetics through the interaction with lipid components. Cholesterol plays a critical role in this interaction.