Mechanism of anesthesia: Anesthetics may restructure the hydrogen belts of membranes

The cut-off effect of n-alcohols in lipid rafts: A lipid-dependent phenomenon☆

n-Aliphatic alcohols act as anesthetics only up to a certain chain length, beyond which its biological activity disappears. This is known as the 'cut-off' phenomenon. Although the most accepted explanation is based on action sites in membrane proteins, it is not well understood why alcohols alter their functions. The structural dependence of these protein receptors to lipid domains known as 'lipid rafts', suggests a new approach to tackle the puzzling phenomenon. In this work, by performing molecular dynamic simulations (MDS) to explore the lipid role, we provide relevant molecular details about the membrane-alcohol interaction at the cut-off point regime. Since the high variability of the cut-off points found on protein receptors in neurons may be a consequence of differences in the lipid composition surrounding such proteins, our results could have a clear-cut importance.

Electrophysiological-mechanical coupling in the neuronal membrane and its role in ultrasound neuromodulation and general anaesthesia

The current understanding of the role of the cell membrane is in a state of flux. Recent experiments show that conventional models, considering only electrophysiological properties of a passive membrane, are incomplete. The neuronal membrane is an active structure with mechanical properties that modulate electrophysiology. Protein transport, lipid bilayer phase, membrane pressure and stiffness can all influence membrane capacitance and action potential propagation. A mounting body of evidence indicates that neuronal mechanics and electrophysiology are coupled, and together shape the membrane potential in tight coordination with other physical properties. In this review, we summarise recent updates concerning electrophysiological-mechanical coupling in neuronal function. In particular, we aim at making the link with two relevant yet often disconnected fields with strong clinical potential: the use of mechanical vibrations-ultrasound-to alter the electrophysiogical state of neurons, e.g., in neuromodulation, and the theories attempting to explain the action of general anaesthetics. STATEMENT OF SIGNIFICANCE: General anaesthetics revolutionised medical practice; now an apparently unrelated technique, ultrasound neuromodulation-aimed at controlling neuronal activity by means of ultrasound-is poised to achieve a similar level of impact. While both technologies are known to alter the electrophysiology of neurons, the way they achieve it is still largely unknown. In this review, we argue that in order to explain their mechanisms/effects, the neuronal membrane must be considered as a coupled mechano-electrophysiological system that consists of multiple physical processes occurring concurrently and collaboratively, as opposed to sequentially and independently. In this framework the behaviour of the cell membrane is not the result of stereotypical mechanisms in isolation but instead emerges from the integrative behaviour of a complexly coupled multiphysics system.

Electron spin changes during general anesthesia in Drosophila

We show that the general anesthetics xenon, sulfur hexafluoride, nitrous oxide, and chloroform cause rapid increases of different magnitude and time course in the electron spin content of Drosophila. With the exception of CHCl3, these changes are reversible. Anesthetic-resistant mutant strains of Drosophila exhibit a different pattern of spin responses to anesthetic. In two such mutants, the spin response to CHCl3 is absent. We propose that these spin changes are caused by perturbation of the electronic structure of proteins by general anesthetics. Using density functional theory, we show that general anesthetics perturb and extend the highest occupied molecular orbital of a nine-residue α-helix. The calculated perturbations are qualitatively in accord with the Meyer-Overton relationship and some of its exceptions. We conclude that there may be a connection between spin, electron currents in cells, and the functioning of the nervous system.

Molecular and cellular mechanisms of general anaesthesia

General anaesthetics are much more selective than is usually appreciated and may act by binding to only a small number of targets in the central nervous system. At surgical concentrations their principal effects are on ligand-gated (rather than voltage-gated) ion channels, with potentiation of postsynaptic inhibitory channel activity best fitting the pharmacological profile observed in general anaesthesia. Although the role of second messengers remains uncertain, it is now clear that anaesthetics act directly on proteins rather than on lipids.

Effect of organic solvents on nervous cell membrane as measured by changes in the (Ca2+/Mg2+) ATPase activity and fluidity of synaptosomal membrane

The effect of various solvents on the central nervous system was studied by using rat brain synaptosomal membranes as an in vitro model. The activity of (Ca2+/Mg2+) ATPase and the membrane fluidity was determined. The alteration of the ATPase activity depended on the physio-chemical characteristics of the solvent in question. Incubation with aliphatic alkanes caused a stimulation of the ATPase activity whereas mixed hydrocarbons as kerosene, white spirit and gasoline inhibited the enzyme. Incubation with chlorinated hydrocarbons caused a biphasic response dependent on the concentration. Oxygen-containing hydrocarbons exhibited various effects as found after incubation with hydrocarbons. The different effects of the solvents on the ATPase activity suggest that the lipophilicity of the solvents is one of more parameters affecting the membrane. Furthermore, the biphasic response following the incubation with chlorinated hydrocarbons indicates that more mechanisms are involved in the enzyme effect. The membrane fluidity is increased with higher concentrations of the solvents. From the results it is concluded that the ATPase activity depends not only on the membrane fluidity and volume, but also on the hydrophilic vicinity of the enzyme molecule.