Effects of non-electrolyte molecules with anesthetic activity on the physical properties of DMPC multilamellar liposomes

Temperature dependence of thermodynamic activity in volatile anesthetics: correlation between anesthetic potency and activity

Temperature dependence of the saturated concentration and the activity coefficient of anesthetics (1-propanol, diethyl ether, chloroform, and halothane) in water were evaluated using vapor pressure and H NMR measurement. We found that these physical values (quantities) correlate with anesthetic potencies estimated according to the thermodynamic equilibrium model. The anesthetic potency for hydrophilic anesthetic (diethyl ether) decreased with decreasing temperature because of the temperature specificity of this saturated concentration. In contrast, potencies of hydrophobic anesthetics (chloroform and halothane) increased with decreasing temperature because of the temperature specificity of those activity coefficients. By assuming that anesthetics interact with hydrated water of cell membranes, the temperature dependence of anesthetic potencies in vivo is qualitatively explicable.

Action mechanism of water soluble ethanol on phospholipid monolayers using a quartz crystal oscillator

Interaction between phospholipid monolayers (dihexadecyl phosphate: DHP, dipalmitoyl phosphatidyl choline: DPPC) and water soluble ethanol has been studied using quartz crystal microbalance (QCM) method and quartz crystal impedance (QCI) method. The quartz crystal oscillator was attached horizontally on the DHP and DPPC monolayers that were formed on the water surface. At low concentration, increased ethanol concentration decreased the frequency for QCM and increased the resistance for QCI. Both frequency and resistance approached asymptotically to a saturation value. A further increase in ethanol concentration induced a sudden and discontinuous linear change (a decrease in frequency and an increase in resistance). Based on these results, we propose the following action mechanism of ethanol on phospholipid monolayers: at low concentration, the ethanol hydrates adsorb into the monolayer/water interface and saturate on the interface. The monolayer viscosity also increases with the adsorption of hydrates. A further increase in concentration causes multilayer formation of hydrates and/or penetration of hydrates into the monolayer core. The viscosity of the interfacial layer (monolayer and interfacial structured water) changes dramatically according to the action of ethanol hydrates.

Low-level hyperbaric exposure antagonizes locomotor effects of ethanol and n-propanol but not morphine in C57BL mice

Low-level hyperbaric exposure antagonizes a broad range of behavioral effects of ethanol in a direct, reversible, and competitive manner. This study investigates the selectivity of the antagonism across other drugs. C57BL/6 mice were injected with saline, ethanol, n-propanol, or morphine sulfate, and then were exposed to 1 atmosphere absolute (ATA) air, 1 ATA helium-oxygen gas mixture (heliox), or 12 ATA heliox. Locomotor activity was measured from 10 to 40 min following injection. N-propanol produced a dose-dependent depression of locomotor activity from 1.0 g/kg. Morphine produced a dose-dependent stimulation of locomotor activity at doses of 3.75-12.0 mg/kg. Exposure to 12 ATA heliox significantly antagonized the locomotor depressant effects of 1.0 g/kg n-propanol and 2.5 g/kg ethanol, without significantly affecting blood concentrations of these drugs measured at 40 min postinjection. Exposure to 12 ATA heliox did not significantly antagonize the locomotor-stimulating effects of the two morphine doses tested (3.75 and 7.5 mg/kg). These findings suggest that exposure to 12 ATA heliox antagonizes the behavioral effects of intoxicant-anesthetic drugs like ethanol and n-propanol, which are believed to act via perturbation or allosteric modulation of functional proteins, but does not antagonize the effects of drugs like morphine, which act via more direct mechanisms. This demonstration of selective antagonism adds important support for the hypothesis that low-level hyperbaric exposure is a direct mechanistic ethanol antagonist, with characteristics similar to a competitive pharmacological antagonist.

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.

Depth-dependent change in membrane fluidity by phenolic compounds in bovine platelets and its relationship with their effects on aggregation and adenylate cyclase activity

The effects of phenolic compounds on membrane fluidity of bovine blood platelets were investigated by studies on the fluorescence anisotropies of diphenylhexatriene (DPH) and its ionic derivatives to clarify the relationship of these effects with the inhibitory effects of the compounds on aggregation. Among the phenolic compounds tested, monohydric phenols (phenol and two monosubstituted derivatives) decreased the fluorescence anisotropy of DPH, which is thought to be located within the hydrophobic core of the membrane, in concentration ranges in which they inhibited platelet aggregation. On the other hand, they had little or no effects on the fluorescence anisotropies of the ionic derivatives of DPH, which are thought to be located in the interfacial region of the lipid bilayer. Consistent with their effects on the fluorescence anisotropy of DPH, these monohydric phenols increased the intracellular cAMP concentration. Thus, these monohydric phenols may inhibit platelet function by stimulation of adenylate cyclase mediated by perturbation of the central region of the membrane lipid bilayer. On the other hand, pyrocatechol and pyrogallol, which have two and three phenolic hydroxyl groups and have much larger electron donor activities than the monohydric phenols tested, inhibited platelet function by a different mechanism, because they did not cause increase in either membrane fluidity or the cAMP concentration of platelets.

Alcohols produce reversible and irreversible acceleration of phospholipid flip-flop in the human erythrocyte membrane

The slow, non-mediated transmembrane movement of the lipid probes lysophosphatidylcholine, NBD-phosphatidylcholine and NBD-phosphatidylserine in human erythrocytes becomes highly enhanced in the presence of 1-alkanols (C2-C8) and 1,2-alkane diols (C4-C8). Above a threshold concentration characteristic for each alcohol, flip rates increase exponentially with the alcohol concentration. The equieffective concentrations of the alcohols decrease about 3-fold per methylene added. All 1-alkanols studied are equieffective at comparable calculated membrane concentrations. This is also observed or the 1,2-alkane diols, albeit at a 5-fold lower membrane concentration. At low alcohol concentrations, flip enhancement is reversible to a major extent upon removal of the alcohol. In contrast, a residual irreversible flip acceleration is observed following removal of the alcohol after a treatment at higher concentrations. The threshold concentrations to produce irreversible flip acceleration by 1-alkanols and 1,2-alkane diols are 1.5- and 3-fold higher than those for flip acceleration in the presence of the corresponding alcohols. A causal role in reversible flip-acceleration of a global increase of membrane fluidity or membrane polarity seems to be unlikely. Alcohols may act by increasing the probability of formation of transient structural defects in the hydrophobic barrier that already occur in the native membrane. Membrane defects responsible for irreversible flip-acceleration may result from alterations of membrane skeletal proteins by alcohols.

Alcohols dehydrate lipid membranes: an infrared study on hydrogen bonding

The effects of alcohols (methanol, ethanol, and n-butanol) on the hydrogen bonding of dipalmitoylphosphatidylcholine (DPPC) were studied by Fourier-transform infrared spectroscopy (FTIR) in water-in-oil (carbon tetrachloride) reversed micelles. The bound O-H stretching mode of water, bonded to DPPC, appeared as a broad band at around 3400 cm-1. The O-H bending mode of this complex appeared as a weak broad band at 1644 cm-1. No free O-H signal was observed. When alcohols were added, a part of DPPC-bound water was replaced by the alcohols. The released 'free' water appeared at 3680 cm-1. This free O-H stretching band represents water-alcohol complex. A new broad band of O-H stretching appeared at 3235 cm-1, which represents the alcohol molecules bound to the phosphate moiety of DPPC. When the alcohol concentration was increased, the intensities of the free O-H stretching and bending bands increased. The P = O- antisymmetric stretching band at 1238 cm-1 became broader and shifted to lower frequencies. This means that alcohols interacted with the phosphate moiety and replaced the bound water. In the deconvoluted spectra of the C = O stretching mode, the ratio between the free sn-2 and the hydrogen-bonded sn-2 bands increased; a part of the bound water at the sn-2 carbon in the glycerol skeleton is also released and the free sn-2 signal increased. From the change in the intensity of the P = O- stretching band, the partition coefficients of alcohols between the phosphate region of DPPC and water were estimated: methanol 7.8, ethanol 16.7 at 22.0 degrees C in mole fraction bases. In molality, these values translates into methanol 0.21 and ethanol 0.45. These results indicate that short-chain alcohols interact with lipid membranes at the phosphate moiety at the hydrophilic head, weaken the membrane-water interaction, and destabilize membranes.

The relationship between brain temperature during intoxication and ethanol sensitivity in LS and SS mice

The present study characterized the relationship between brain temperature, rectal temperature, and ethanol sensitivity in the selectivity bred long-sleep (LS) and short-sleep (SS) mice. Radiotelemetric brain probe implanted and nonimplanted LS/lbg and SS/lbg male mice were injected with 2.5 and 4.9 g/kg ethanol, respectively, before exposure to ambient temperatures of 15 degrees C, 22 degrees C, or 34 degrees C. Ambient temperature significantly affected rectal temperature, brain temperature, and ethanol sensitivity, measured by impairment of righting reflex. Brain and rectal temperatures at return of righting reflex (RORR) were highly correlated. In SS mice brain and rectal temperatures at RORR were significantly positively correlated with loss of righting reflex (LORR) duration and significantly negatively correlated with blood ethanol concentration (BEC) at RORR. In LS mice rectal temperature at RORR was significantly negatively correlated with LORR duration, while both brain and rectal temperature at RORR were significantly positively correlated with BEC at RORR. The strength of the correlations and r2 values generated from linear regression analysis indicates that body temperature during intoxication can explain up to 52% of the variability in ethanol sensitivity in SS mice, but only 19% of the variability in ethanol sensitivity in LS mice. The correlational analyses are consistent with previous results based on comparisons between rectal temperature and ethanol sensitivity and extend to direct brain temperature measurement the evidence that decreasing temperature during intoxication decreases ethanol sensitivity in SS mice and increases ethanol sensitivity in LS mice.(ABSTRACT TRUNCATED AT 250 WORDS)

High pressure antagonism of alcohol effects on the main phase-transition temperature of phospholipid membranes: biphasic response

The combined effects of high pressure (up to 300 bar) and a homologous series of 1-alkanols (ethanol C2 to 1-tridecanol C13) were studied on the main phase-transition temperature of dipalmitoylphosphatidylcholine (DPPC) vesicle membranes. It is known that short-chain alkanols depress and long-chain alkanols elevate the main transition temperature. The crossover from depression to elevation occurs at the carbon-chain length about C10-C12 in DPPC vesicle membranes coinciding with the cutoff chain-length where anesthetic potency suddenly disappears. Alkanols shorter than C8 linearly decreased the transition temperature and high pressure antagonized the temperature depression. Alkanols longer than C10 showed biphasic dose-response curves. High pressure enhanced the biphasic response. In addition, alkanols longer than the cutoff length depressed the transition temperature under high pressure at the low concentration range. These non-anesthetic alkanols may manifest anesthetic potency under high pressure. At higher concentrations, the temperature elevatory effect was accentuated by pressure. This biphasic effect of long-chain alkanols is not related to the 'interdigitation' associated with short-chain alkanols. The increment of the transition temperature by pressure was 0.0242 K bar-1 in the absence of alkanols. The volume change of the transition was estimated to be 27.7 cm3 mol-1. This value stayed constant to the limit of the present study of 300 bar.

Membranes and the genetics of ethanol response

A combination of fluorescence polarization (FPZ) and nuclear magnetic resonance (NMR) techniques have revealed that ethanol has diverse and domain dependent effects on membrane order. Under some conditions, in the more superficial membrane domains, ethanol actually orders rather disorders membrane structure. Using 1H-NMR we have examined in synaptic membranes from LS and SS mice the effects of ethanol-d6 on membrane order. The lines differ most significantly in terms of the ethanol effects on the choline methyl resonances. Ethanol was significantly more potent in increasing choline methyl resonance intensity in LS synaptic membranes than in SS synaptic membranes; these data are interpreted to show a significantly greater disordering of the superficial domains in the LS membranes. The maximum ethanol effect was observed between 0.3% and 0.5% for the concentration range studied (0.1 to 1.0%). The methylene resonance data in general paralleled the choline methyl resonance data but with a somewhat attenuated response. Ethanol had only small effects on the terminal methyl resonance in both lines. Overall, we conclude that the LS and SS mice differ in the ethanol-induced perturbation of membrane structure, primarily at more superficial membrane domains.

Interfacial dehydration by alcohols: hydrogen bonding of alcohols to phospholipids

The interaction between alcohols (ethanol and n-butanol) and dipalmitoylphosphatidylcholine (DPPC) in carbon tetrachloride was studied by Fourier transform infrared spectroscopy (FTIR). Upon addition of the alcohols, the P = O stretching band of DPPC at 1260 cm-1 shifted to lower frequency (red-shift). The red-shift indicates that the P = O vibration became slower possibly because the heavier alcohol molecules replaced the water molecules hydrogen bonded to the PO2 moiety. The formation constants between the PO2 group and ethanol or n-butanol (n-butanol data in parenthesis) were 19.0 M-1 (7.1 M-1) when estimated from the spectral change. A new absorbance peak appeared at 3265 cm-1 (3275 cm-1) representing the DPPC-alcohol complex. The formation constant of this complex was also 19.0 M-1 (7.1 M-1). The identical formation constant suggests that the DPPC-alcohol complex was formed at the PO2 moiety of DPPC with hydrogen bonding to the alcohol OH. At higher alcohol concentrations, the absorbance peak of DPPC-alcohol complex shifted to 3225 cm-1 (3235 cm-1). Apparently, the lower frequency shift at higher alcohol concentration occurred by the formation of alcohol multimers (dimer, trimer, and tetramer) interacting with DPPC.

Temperature alters ethanol-induced fluidization of C57 mouse brain membranes

The interaction between temperature and ethanol-induced fluidization was investigated in brain synaptic plasma membranes from C57BL/6 mice. Changes in fluidity were measured using the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene. Fluorescence polarization was tested in the presence and absence of ethanol at 25, 32 and 37 degrees C. An increase in temperature resulted in a significant increase in the baseline fluidity of the membranes and an increase in the magnitude of ethanol-induced fluidization of brain membranes. The combined effect of temperature on baseline fluidity and the magnitude of the response to ethanol resulted in a significant temperature-related increase in the relative response to ethanol (% change in polarization). The minimum concentration of ethanol required to cause a significant increase in the fluidity of the membranes was 170.7 mM at 25 degrees C and 85.3 mM at both 32 and 37 degrees C. The present results indicate that temperature-related changes in the effects of ethanol on membrane properties may underlie the effects of temperature on ethanol sensitivity in C57 mice.

A solid-solution theory of anesthetic interaction with lipid membranes: temperature span of the main phase transition

Anesthetics (or any other small additives) depress the temperature of the main phase transition of phospholipid bilayers. Certain anesthetics widen the temperature span of the transition, whereas others do not. The widening in a first-order phase transition is intriguing. In this report, the effects of additive molecules on the temperature and its span were explained by the solid-solution theory. By assuming coexistence of the liquid-crystal and solid-gel phases of lipid membranes at phase transition, the phase boundary is determined from the distribution of anesthetic molecules between the liquid-crystal membrane versus water and between the solid-gel membrane versus water. The theory shows that when the lipid concentration is large or when the lipid solubility of the drug is large, the width of the transition temperature increases, and vice versa. Highly lipid-soluble molecules, such as long-chain alkanols and volatile anesthetics, increase the width of the transition temperature when the lipid:water ratio is large, whereas highly water-soluble molecules, such as methanol and ethanol, do not. The aqueous phase serves as the reservoir for anesthetics. Depletion of the additive molecules from the aqueous phase is the cause of the widening. When the reservoir capacity is large, the temperature width does not increase. The theory also predicts asymmetry of the specific heat profile at the transition.