Do clinical levels of general anaesthetics affect lipid bilayers? Evidence from Raman scattering.

We have used Raman spectroscopy to investigate the effects of the general anaesthetics halothane and chloroform on lipid bilayer order. Clinical concentrations of these anaesthetics had no significant effect on the hydrocarbon chain conformation in multilamellar vesicles of dimyristoylphosphatidylcholine/cholesterol. This result was obtained with a technique sufficiently precise to monitor changes in the acyl chain trans-gauche population ratio associated with a 1-2 K alteration in temperature. Very high levels of anaesthetics caused a marked disordering of the hydrocarbon chains. The danger of inferring an effect at clinical concentrations from data obtained at much higher levels is illustrated by a statistical analysis of our dose-response curves.