Effects of anesthetics on water permeability and lipid metabolism in Acholeplasma laidlawii membranes.

The addition of tetracaine and diethyl ether to Acholeplasma laidlawii at concentrations commonly used for local anesthesia did not affect water permeability over the cell membrane, as measured by a pulsed magnetic field gradient NMR method. However, A. laidlawii changed its membrane lipid composition upon treatment with these anesthetics. Both tetracaine and diethyl ether addition resulted in a decrease in the molar ratio between the major membrane glucolipids, monoglucosyldiacylglycerol and diglucosyldiacylglycerol. The ratio between saturated and unsaturated acyl chains did not change. The results are in accordance with our proposal that A. laidlawii regulates its lipid composition in order to maintain optimal packing stability in the membrane (Wieslander, A., Christiansson, A., Rilfors. L. and Lindblom, G. (1980) Biochemistry 19, 3650--3655). Introduction of anesthetics into the hydrophobic region of a bilayer is likely to affect the lipid packing. A membrane which contains lipids like monoglucosyldiacylglycerol, which forms a reversed hexagonal phase, will be destabilized unless the amounts of such lipids are reduced. The membrane concentration of anesthetics was estimated to one molecule per 12--15 lipid molecules. The fact that A. laidlawii regulates its lipid composition as a response to these concentrations, despite their negligible effect on water permeability, indicates a high sensitivity of this regulatory system.