1-2-oleoylphosphatidylcholine and 1-hexanol

The trend of evidence suggests that general anesthetics act directly on proteins in the neural membrane. However, the fact that the functions of nicotinic acetylcholine receptor (sodium permeability, desensitization rate) are modulated by the composition of the membrane in which it is reconstituted has been thought to be a result of the variation of interactions between acetylcholine receptor and membrane. In this study, protein-lipid interaction at the level of the lipid headgroup was investigated using electron paramagnetic resonance (EPR) and headgroup spin label. Lipid headgroup mobility was evaluated with rotational correlation time from the EPR spectrum. Protein-lipid interaction at headgroup depth was demonstrated from the motionally restricted component of the spectrum. Rotational correlation time increased to 13 ns from 7 ns due to protein-lipid interaction. The effect of anesthetic (ethanol, 1-hexanol, and isoflurane) on protein-lipid interaction was investigated, and the correlation time was 13 ns. It is concluded that the anesthetics used in this study did not alter protein-lipid interaction at the level of the lipid headgroup, so far as observed by rotational correlation time, without excluding the possibility that anesthetics that perturb protein-lipid interactions modulate receptor functions via this mechanism.

Topics: Alcohols; Anesthetics, Inhalation; Electron Spin Resonance Spectroscopy; Ethanol; Hexanols; Isoflurane; Lipid Bilayers; Lipids; Phosphatidylcholines; Receptors, Nicotinic; Spin Labels

The interaction of general anesthetics at the lipid/protein interface of the nicotinic acetylcholine receptor reconstituted in dioleoylphosphatidylcholine bilayers at various lipid/protein ratios has been studied using the electron spin resonance spectra of phosphatidylcholine spin-labeled at the fourteenth acyl carbon (14-PCSL). In addition to the bilayer spectrum, the spin label reported a more motionally restricted environment whose contribution increased with increasing protein/lipid ratio. Exchange between these two environments occurred at a rate of approx. 6 x 10(7) s-1. The motionally restricted, protein-associated 14-PCSL had a rotational correlation time of about 10-20 ns, an order of magnitude slower than when in the bilayer. Addition of 1-hexanol (up to 16 mM) to the reconstituted receptor perturbed the acyl chains of the bulk lipid phase, but the motional properties of the lipid acyl chains at the protein/lipid interface near the membrane center were not significantly perturbed on the EPR motional time-scale. Similarly, anesthetics that were less effective at perturbing the bilayer, such as pentobarbital (up to 2 mM) and isoflurane (7 mM), did not perturb the lipid/protein interface on the conventional EPR motional time scale.

Topics: Anesthesia, General; Anesthetics; Animals; Hexanols; Lipid Bilayers; Phosphatidylcholines; Receptors, Nicotinic; Torpedo