A STUDY OF THE EFFECT OF GENERAL-ANESTHETICS ON LIPID PROTEIN INTERACTIONS IN ACETYLCHOLINE-RECEPTOR ENRICHED MEMBRANES FROM TORPEDO-NOBILIANA USING NITROXIDE SPIN-LABELS

Stearic acid, phosphatidylcholine, and phosphatidylglycerol nitroxide spin-labels were used to probe the effect of 1-hexanol, urethane, diethyl ether, and ethanol on lipid-protein interactions in nicotinic acetylcholine receptor (nAcChoR) rich membranes from Torpedo nobiliana. For stearic acid spin-labeled at the C-14 position of the sn-l acyl chain, 1-hexanol induced little change (over a wide concentration range, 0–16.7 mM) in either the ESR line shape or the proportion of motionally restricted spectral component from labels probing the protein interface. The main effect of 1-hexanol was limited to an increase in the mobility of stearic acid spin-labels probing the non-protein-associated environment. In contrast, for C-14 phosphatidylcholine spin-la bel, 1-hexanol decreased the fraction of spin-labels motionally restricted at the protein interface from 0.33 without 1-hexanol to 0.20 with 16.7 mM 1-hexanol, with no change in the line shape of the spectral component of these labels. The ESR spectral line shape of the fluid component due to phosphatidylcholine labels in sites away from the protein interface displayed a gradual decrease in spectral anisotropy on addition of increasing amounts of 1-hexanol. At a concentration of 1-hexanol that desensitizes half the receptors, the fraction of motionally restricted phosphatidylcholine spin-label is reduced by approximately 15%. The effect of 1-hexanol on phosphatidylglycerol spin-labels was intermediate between these two cases. Similar effects were measured with other general anesthetics, including urethane, diethyl ether, and ethanol. Thus, action at the lipid-protein interface by general anesthetics provides a plausible alternative molecular mechanism for desensitization of the nAcChoR, and possibly general anesthesia, but does not preclude some synergistic lipid disordering by anesthetics of the surrounding bilayer. © 1990, American Chemical Society. All rights reserved.