Effects of ethanol and calcium on lipid order of membranes from mice selected for genetic differences in ethanol intoxication

Effects of acute alcohol exposure and chronic alcohol use on neurite orientation dispersion and density imaging (NODDI) parameters

RATIONALE

Little is known about how acute and chronic alcohol exposure may alter the in vivo membrane properties of neurons.

OBJECTIVES

We employed neurite orientation dispersion and density imaging (NODDI) to examine acute and chronic effects of alcohol exposure on neurite density.

METHODS

Twenty-one healthy social drinkers (CON) and thirteen nontreatment-seeking individuals with alcohol use disorder (AUD) underwent a baseline multi-shell diffusion magnetic resonance imaging (dMRI) scan. A subset (10 CON, 5 AUD) received dMRI during intravenous infusions of saline and alcohol during dMRI. NODDI parametric images included orientation dispersion (OD), isotropic volume fraction (ISOVF), and corrected intracellular volume fraction (cICVF). Diffusion tensor imaging metrics of fractional anisotropy and mean, axial, and radial diffusivity (FA, MD, AD, RD) were also computed. Average parameter values were extracted from white matter (WM) tracts defined by the Johns Hopkins University atlas.

RESULTS

There were group differences in FA, RD, MD, OD, and cICVF, primarily in the corpus callosum. Both saline and alcohol had effects on AD and cICVF in WM tracts proximal to the striatum, cingulate, and thalamus. This is the first work to indicate that acute fluid infusions may alter WM properties, which are conventionally believed to be insensitive to acute pharmacological challenges. It also suggests that the NODDI approach may be sensitive to transient changes in WM. The next steps should include determining if the effect on neurite density differs with solute or osmolality, or both, and translational studies to assess how alcohol and osmolality affect the efficiency of neurotransmission.

Biological water and its role in the effects of alcohol

Alcohol and water compete with each other on target membrane molecules, specifically, lipids and proteins near the membrane surface. The basis for this competition is the hydrogen bonding capability of both compounds. But alcohol's amphiphilic properties give it the capability to be attracted simultaneously to both hydrophobic and hydrophilic targets. Thus, alcohol could bind certain targets preferentially and displace water, leading to conformational consequences. This article reviews the clustering and organized character of biological water, which modulates the conformation of membrane surface molecules, particularly receptor protein. Any alcohol-induced displacement of biological water on or inside of membrane proteins creates the opportunity for allosteric change in membrane receptors. This interaction may also prevail in organelles, such as the Golgi apparatus, which have relatively low concentrations of bulk water. Target molecules of particular interest in neuronal membrane are zwitteronic phospholipids, gangliosides, and membrane proteins, including glycoproteins. FTIR and NMR spectroscopic evidence from model membrane systems shows that alcohol has a nonstereospecific binding capability for membrane surface molecules and that such binding occurs at sites that are otherwise occupied by hydrogen-bonded water. The significance of these effects seems to lie in the need to learn more about biological water as an active participant in biochemical actions. Proposed herein is a new working hypothesis that the molecular targets of ethanol action most deserving of study are those where water is trapped and there is little bulk water. Proteins (enzymes and receptors) certainly differ in this regard, as do organelles.

Neurochemical bases of locomotion and ethanol stimulant effects

The locomotor stimulant effect produced by alcohol (ethanol) is one of a large number of measurable ethanol effects. Ethanol-induced euphoria in humans and locomotor stimulation in rodents, a potential animal model of human euphoria, have long been recognized and the latter has been extensively characterized. Since the euphoria produced by ethanol may influence the development of uncontrolled or excessive alcohol use, a solid understanding of the neurochemical substrates underlying such effects is important. Such an understanding for spontaneous locomotion and for ethanol's stimulant effects is beginning to emerge. Herein we review what is known about three neurochemical substrates of locomotion and of ethanol's locomotor stimulant effects. Several lines of research have implicated dopaminergic, GABAergic, and glutamatergic neurotransmitter systems in determining these behaviors. A large collection of work is cited, which strongly implicates the above-mentioned neurotransmitter substances in the control of spontaneous locomotion. A smaller, but persuasive, body of evidence suggests that central nervous system processes utilizing these transmitters are involved in determining the effects of ethanol on locomotion. Particular emphasis has been placed on the mesolimbic ventral tegmental area to nucleus accumbens dopaminergic pathway, and on the ventral pallidum/substantia innominata, where GABA and glutamate have been found to play a role in altering the activity of this dopaminergic pathway. Research on ethanol and drug locomotor sensitization, increased responsiveness to the substance with repeated administration, is also reviewed as a process that may be important in the development of drug addiction.

Chronic ethanol consumption alters effects of ethanol in vitro on brain membrane structure of high alcohol sensitivity and low alcohol sensitivity rats

In this study, we examined if differences in initial membrane sensitivity to ethanol were associated with development of membrane tolerance to ethanol. High Alcohol Sensitivity (HAS) and Low Alcohol Sensitivity (LAS) rats were administered a 15% ethanol solution in water as the sole source of fluid for 30 days. The amount of ethanol consumed per day did not significantly differ between the HAS and LAS rats. Development of membrane tolerance to in vitro effects of ethanol has been previously reported for bulk membrane fluidity and protein-lipid interaction. Our data expands the understanding of "membrane tolerance" phenomenon to protein distribution and bilayer interdigitation. We also introduce genotype-dependent and genotype-independent properties of the membrane tolerance to ethanol. ethanol treatment produced genotype-dependent and genotype-independent membrane tolerance to ethanol. The in vitro effects of ethanol on synaptic plasma membrane (SPM) protein distribution and lipid bilayer interdigitation were abolished or decreased in the SPM of chronic ethanol-treated HAS rats, as compared with the SPM of HAS control rats (genotype-dependent tolerance). Protein distribution and bilayer interdigitation were not affected by ethanol in vitro in either chronic ethanol-treated or control LAS rats. Genotype-independent tolerance to ethanol in vitro was observed for SPM annular and bulk bilayer fluidity in chronic ethanol-treated HAS and LAS rats. It is concluded that initial sensitivity to ethanol contributes to the development of membrane tolerance to ethanol in HAS and LAS rats.

Chronic ethanol consumption affects cholinoceptor- and purinoceptor-mediated contractions of the isolated rat bladder

Isolated bladder strips from 12-week ethanol-fed, pair-fed and control adult male rats were investigated. Contractile responses to carbachol (CCh; 0.1-300 microM) were statistically significantly potentiated in the ethanol-fed group compared to pair-fed and control. Contractions to beta,gamma-methylene ATP (beta,gamma-MeATP; 1-300 microM) were statistically significantly potentiated in the ethanol-fed group at the highest concentration tested (300 microM). Neurogenic contractions (0.5-32 pps) from the ethanol-fed group in the absence of atropine and after desensitisation by alpha,beta-methylene ATP (alpha,beta-MeATP; 3 microM), were significantly potentiated compared to the pair-fed and control groups; in the presence of atropine (1 microM), neurogenic contractions were significantly augmented at the higher frequencies. It is concluded that chronic ethanol treatment affects both cholinoceptor- and purinoceptor-mediated contractions of the rat bladder.

Characterization of a GM1-dependent surface interaction for alcohol with DPPC membranes

A unique surface interaction for perdeuterated ethanol and 1-butanol with dipalmitoylphosphatidylcholine (DPPC)/monosialoganglioside (GM1) multilamellar vesicles can be detected from the fast exchange averaging of the nuclear quadrupole coupling constant of the alcohol in the free and bound states using deuterium NMR. At 1.0% perdeuterated ethanol or 0.5% perdeuterated 1-butanol, a small splitting of the alcohol resonance(s) was detected in the liquid-crystalline phase, but not in the gel phase of the bilayer. The observed splitting is proportional to the fraction of alcohol bound and is dependent on temperature, alcohol, and GM1 concentrations. The splitting was only observed in the presence of negatively charged GM1 but not neutral asialoganglioside (asialo-GM1) in DPPC multilamellar vesicles. The observed splitting decreased with the addition of Ca2+ or Mg2+ ions. This effect was reversed upon the addition of chelating agents. It is proposed that the unique surface interaction for alcohol may result from small surface perturbations of the phosphatidylcholine head groups by the negatively charged sialic moieties of neighboring GM1 molecules in the bilayer.

Ethanol disordering of GM1-enriched short-sleep synaptosomal plasma membranes

The Long-Sleep (LS) and Short-Sleep (SS) mouse synaptosomal plasma membranes differ in ethanol sensitivity at superficial membrane regions, which corresponds with the behavioral response of the mice to ethanol hypnosis. The only significant difference between these synaptosomal plasma membranes is the synaptosomal monosialoganglioside (GM1) content, LS > SS. Here, GM1 was examined as a parameter for increasing membrane sensitivity to ethanol effects in the ethanol-resistant SS membranes. Synaptosomal plasma membranes from SS mice were allowed to incorporate exogenous GM1. Membrane order was then studied at the surface, intermediate, and interior regions of the membranes by delayed Fourier transform proton NMR in the presence and absence of perdeuterated ethanol. Differences in membrane order were observed in all three membrane regions with increasing perdeuterated ethanol concentrations depending on the synaptosomal GM1 content.

Effects of ethanol on structural parameters of rat brain membranes: relationship to genetic differences in ethanol sensitivity

Fluorescent probes located in different membrane regions were used to evaluate effects of ethanol (50 and 100 mM) on structural parameters (protein distribution, fluidity of total and annular lipid, and thickness of the bilayer) of synaptic plasma membranes (SPMs) from brain cortex of High-Alcohol Sensitivity (HAS) and Low-Alcohol Sensitivity (LAS) rats. An experimental procedure based on radiationless energy transfer from tryptophan of membrane proteins to pyrene, 1,3-bis-(1-pyrene)propane(pyr-C3-pyr), or 1,6-diphenyl-1,3,5-hexatriene (DPH), as well as pyr-C3-pyr monomer-eximer formation and DPH polarization, and energy transfer from pyrene monomers to 1-anilinonaphthalene-8-sulfonic acid (ANSA) was utilized. The efficiency of energy transfer from tryptophan to pyrene was sensitive to protein clustering induced in SPMs by concanavalin A. Efficiency of energy transfer from pyrene monomers to ANSA was different for vesicles of dimyristoyl phosphatidyl choline, dipalmitoyl phosphatidyl choline, and distearoyl phosphatidyl choline, consistent with differences in the thickness of these lipid bilayers. Without ethanol, there were no significant differences between the structural parameters of SPMs from HAS and from LAS rats. Addition of ethanol (50 mM) changed protein distribution (increased clustering) only in membranes from HAS rats and had no effect on the structure of membranes from LAS rats. A larger concentration of ethanol (100 mM) changed the fluidity of annular and total lipid in both lines of rats, but changed protein distribution and decreased thickness of the membranes from HAS rats with no effect on these parameters in SPMs from LAS animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective breeding for initial sensitivity to ethanol

Selective breeding for initial sensitivity to ethanol has been carried out by a number of investigators in order to investigate the mechanisms by which ethanol brings about a myriad of effects on the mammalian central nervous system. In addition the availability of these selectively bred animals provides clues to the causes of the genetic predisposition of humans to alcoholism. Eventually it is envisioned that the synteny between the mouse and human genomes will allow identification of specific genes responsible for acute effects of ethanol in both species as well as clues as to how alcoholism in humans can be better identified, prevented, and treated.

Effect of an homologous series of aliphatic alcohols on neuronal and smooth muscle voltage-dependent Ca2+ channels

The acute inhibitory actions of alcohol on K(+)-stimulated 45Ca2+ uptake into synaptosomes shows regional variation in sensitivity throughout the brain, suggesting the possibility of a selective action on a specific Ca2+ channel subtype. This was examined by comparing the effects of a homologous series of aliphatic alcohols on synaptosomal Ca2+ channels with their actions on K(+)-stimulated Ca2+ channels in guinea-pig intestinal longitudinal muscle, which have been demonstrated to be of the L-type. K(+)-stimulated contraction of and [3H]nitrendipine binding to smooth muscle were both inhibited by the alcohols at similar concentrations, with the potency increasing with chain length. In synaptosomes, however, K(+)-stimulated 45Ca2+ uptake was 5-30 times more sensitive to the inhibitory actions of alcohol than were [3H]nitrendipine and [125I]omega-conotoxin binding. These observations suggest that K(+)-stimulated 45Ca2+ uptake is mediated by a non-L non-N type channel which is more sensitive to the acute effects of alcohols. This is supported by the observation that K(+)-stimulated 45Ca2+ uptake which is insensitive to L- and N-channel antagonists was inhibited by funnel web spider venom.

Surface exposure of synaptosomal gangliosides from long-sleep and short-sleep mice

A galactose oxidase/NaB[3H]4 technique was used to examine the relative surface exposure of gangliosides from whole brain synaptosomes of long-sleep (LS) and short-sleep (SS) mice. The surface exposure of the monosialoganglioside, GM1, did not differ between the two lines. Surface exposure of the polysialogangliosides GD1a, GD1b, and GT1b, however, was significantly greater in LS synaptosomes than in SS. Hydrolysis of the polysialogangliosides by neuraminidase to the end-product, GM1, at early time periods occurred more rapidly in LS than in SS synaptosomes. Upon exposure to either 250 mM or 50 mM ethanol, LS synaptosomal ganglioside surface exposure was decreased, but that of SS was increased. Pairwise comparisons of the individual ganglioside classes indicated that the decrease in LS synaptosomal ganglioside surface exposure was attributable to decreases in the polysialogangliosides, compared with controls. The ethanol-induced increase in SS synaptosomal ganglioside surface exposure, however, was mainly due to an increased surface exposure of only GD1a. These results suggest that intrinsic differences in the surface exposure of gangliosides and/or the magnitude and direction of ethanol-induced changes in ganglioside surface distribution may reflect biophysical or modulatory mechanisms by which this class of compounds modifies membrane sensitivity to ethanol. These results suggest that further studies should be performed to determine whether gangliosides are factors in genetically determined sensitivity to ethanol.

Ceramide composition of whole brain synaptosomal gangliosides from mice genetically bred for divergent ethanol sensitivities

A comparison of the two major ceramide molecular species (d18:1-C18:0 and d20:1-C18:0) of synaptosomal gangliosides GM1, GD1a+GT1a, GD1b, GT1b, revealed a difference between the ceramide composition of ethanol-sensitive LS and ethanol-insensitive SS whole brain synaptosomal gangliosides. In all comparisons, the ratio of the two major molecular species, (d18:1-C18:0/d20:1-C18:0) was less for LS than for SS mice.

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)

Biophysical and biochemical alterations in erythrocyte membranes from chronic alcoholics

Erythrocyte membranes from healthy controls and alcoholic patients, examined within 24 h of abstinence, were studied for basal membrane fluidity and membrane sensitivity to ethanol by fluorescence polarization of the apolar probe 1,6-diphenyl-1, 3,5-hexatriene (DPH) and its cationic derivative 1,4(trimethylammonium phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH). The membrane partition (Kp) of ethanol and phenobarbital, and the concentrations of membrane-bound sialic acid and galactose, were also determined. The apolar hydrocarbon region of the membrane (DPH) was less fluid, in the alcoholics than in the controls (p less than 0.005). In the patients this membrane layer, as well as the polar lipid head group region (TMA-DPH), showed reduced fluidizing effect of ethanol (p less than 0.01). This resistance or tolerance to ethanol correlated with a markedly impaired (-59%, p less than 0.025) partition of ethanol into the membrane. The low Kp of ethanol in turn was partly related to reduced concentrations of polar carbohydrates such as sialic acid and galactose (p less than 0.01) at the membrane surface. The Kp of phenobarbital was reduced in the patients (-59%, p less than 0.005) but, apparently unrelated to the carbohydrate changes. These results indicate that in man, chronic alcohol abuse is associated with complex changes of membrane properties at different membrane levels e.g. at the charged surface, in the polar lipid head group region and in the hydrocarbon core. A partial basis for biophysical membrane tolerance to ethanol is suggested, implying that apart from phospholipid alterations, structural changes in membrane-bound glycoconjugates participate in this adaptive process.

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.

The role of neuronal calcium channels in dependence on ethanol and other sedatives/hypnotics

This review discusses the importance of neuronal calcium currents in dependence on ethanol, barbiturates, benzodiazepines and opiates. The main sections describe the actions of ethanol on control of intracellular calcium and on calcium and calcium-dependent conductance mechanisms. In particular, the effects of both acute and chronic ethanol treatment on dihydropyridine-sensitive, voltage-dependent, calcium channels are described. The later sections cover the effects of barbiturates, benzodiazepines and opiates on these systems. The conclusions suggest that dihydropyridine calcium channel antagonists may offer a new therapeutic approach to the treatment of ethanol and opiate dependence.

Selected mouse lines, alcohol and behavior

The technique of selective breeding has been employed to develop a number of mouse lines differing in genetic sensitivity to specific effects of ethanol. Genetic animal models for sensitivity to the hypnotic, thermoregulatory, excitatory, and dependence-producing effects of alcohol have been developed. These genetic animal models have been utilized in numerous studies to assess the bases for those genetic differences, and to determine the specific neurochemical and neurophysiological bases for ethanol's actions. Work with these lines has challenged some long-held beliefs about ethanol's mechanisms of action. For example, lines genetically sensitive to one effect of ethanol are not necessarily sensitive to others, which demonstrates that no single set of genes modulates all ethanol effects. LS mice, selected for sensitivity to ethanol anesthesia, are not similarly sensitive to all anesthetic drugs, which demonstrates that all such drugs cannot have a common mechanism of action. On the other hand, WSP mice, genetically susceptible to the development of severe ethanol withdrawal, show a similar predisposition to diazepam and phenobarbital withdrawal, which suggests that there may be a common set of genes underlying drug dependencies. Studies with these models have also revealed important new directions for future mechanism-oriented research. Several studies implicate brain gamma-aminobutyric acid and dopamine systems as potentially important mediators of susceptibility to alcohol intoxication. The stability of the genetic animal models across laboratories and generations will continue to increase their power as analytic tools.

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

The effects of 13 non-electrolytes with moderate anesthetic potency on the order of DMPC liposomes were examined. Changes in order were monitored by steady-state fluorescence polarization techniques using 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPG). At 30 degrees C, all of the compounds tested decreased the DPH steady-state anisotropy (rs), with potencies highly correlated to their oil/water partition coefficients. However, only the most hydrophobic anesthetics decreased TMA-DPH RS. Some of the most hydrophilic compounds, including ethanol and urethane, actually increased TMA-DPH rs, suggestive of an increase in membrane order. The concept of selectivity was borrowed from partitioning theory and used to explain some effects on anesthetic potency of decreasing temperature to 18 degrees C. In the gel as opposed to the liquid crystalline phase, selectivity for decreasing membrane order (as monitored by DPH) markedly increased, suggesting that anesthetic partitioning and/or the site of anesthetic action was occurring in a more hydrophobic domain. The solute-independent difference (or capacity) between two membranes for perturbation was defined as membrane sensitivity. Sensitivity appeared to also decrease with decreasing temperature, despite the decrease in membrane partitioning. This effect is thought to result from the selective delivery of the anesthetic solute to the membrane interior and away from more hydrophilic domains where anesthetics may order membrane structure.