Brain (Na+,K+)-ATPase. Opposite effects of ethanol and dimethyl sulfoxide on temperature dependence of enzyme conformation and univalent cation binding

Effect of Temperature and Ionic Substitutions on the Tegumental Potentials of Protoscoleces of Echinococcus granulosus

The protoscolex (PSC) is generated by asexual reproduction at the larval stage of taeniid Echinococcus granulosus that causes cystic echinococcosis or hydatidosis, a worldwide zoonosis. The PSC is enveloped by a complex cellular syncytial tegument responsible for ionic movements and the hydroelectrolytic balance of the parasite. We recently reported on two electrical potentials in bovine lung protoscoleces (PSCs) that reflect differences in ionic movements between the parasite's invaginated and evaginated developmental stages. Here, we explored the effect of temperature and ionic substitutions on the tegumental potentials of bovine lung PSCs of Echinococcus granulosus by microelectrode impalements. We observed that the transient peak potential was temperature-dependent, consistent with an active transport component in the invaginated state only. Further changes in the electrical potentials by high K⁺ depolarization, low external Ca²⁺, and addition of the diuretic amiloride are in agreement with the presence of a Ca²⁺-sensitive cation-selective electrodiffusional pathway in the outer surface of the parasite. Variations in electrical potential differences through the tegument provide an accessible and valuable parameter for studying ionic transport mechanisms and, therefore, potential targets for developing novel antiparasitic drugs.

Simulation of alcohol action upon a detailed Purkinje neuron model and a simpler surrogate model that runs >400 times faster

BACKGROUND

An approach to investigate brain function/dysfunction is to simulate neuron circuits on a computer. A problem, however, is that detailed neuron descriptions are computationally expensive and this handicaps the pursuit of realistic network investigations, where many neurons need to be simulated.

RESULTS

We confront this issue; we employ a novel reduction algorithm to produce a 2 compartment model of the cerebellar Purkinje neuron from a previously published, 1089 compartment model. It runs more than 400 times faster and retains the electrical behavior of the full model. So, it is more suitable for inclusion in large network models, where computational power is a limiting issue. We show the utility of this reduced model by demonstrating that it can replicate the full model's response to alcohol, which can in turn reproduce experimental recordings from Purkinje neurons following alcohol application.

CONCLUSIONS

We show that alcohol may modulate Purkinje neuron firing by an inhibition of their sodium-potassium pumps. We suggest that this action, upon cerebellar Purkinje neurons, is how alcohol ingestion can corrupt motor co-ordination. In this way, we relate events on the molecular scale to the level of behavior.

Alcohol excites cerebellar Golgi cells by inhibiting the Na+/K+ ATPase

Alcohol-induced alterations of cerebellar function cause motor coordination impairments that are responsible for millions of injuries and deaths worldwide. Cognitive deficits associated with alcoholism are also a consequence of cerebellar dysfunction. The mechanisms responsible for these effects of ethanol are poorly understood. Recent studies have identified neurons in the input layer of the cerebellar cortex as important ethanol targets. In this layer, granule cells (GrCs) receive the majority of sensory inputs to the cerebellum through the mossy fibers. Information flow at these neurons is gated by a specialized pacemaker interneuron known as the Golgi cell, which provides divergent GABAergic input to thousands of GrCs. In vivo electrophysiological experiments have previously shown that acute ethanol exposure abolishes GrC responsiveness to sensory inputs carried by mossy fibers. Slice electrophysiological studies suggest that ethanol causes this effect by potentiating GABAergic transmission at Golgi cell-to-GrC synapses through an increase in Golgi cell excitability. Using patch-clamp electrophysiological techniques in cerebellar slices and computer modeling, we show here that ethanol excites Golgi cells by inhibiting the Na(+)/K(+) ATPase. Voltage-clamp recordings of Na(+)/K(+) ATPase currents indicated that ethanol partially inhibits this pump and this effect could be mimicked by low concentrations of ouabain. Partial inhibition of Na(+)/K(+) ATPase function in a computer model of the Golgi cell reproduced these experimental findings. These results establish a novel mechanism of action of ethanol on neuronal excitability, which likely has a role in ethanol-induced cerebellar dysfunction and may also contribute to neuronal functional alterations in other brain regions.

Chronic alcohol exposure alters transcription broadly in a key integrative brain nucleus for homeostasis: the nucleus tractus solitarius

Chronic exposure to alcohol modifies physiological processes in the brain, and the severe symptoms resulting from sudden removal of alcohol from the diet indicate that these modifications are functionally important. We investigated the gene expression patterns in response to chronic alcohol exposure (21–28 wk) in the rat nucleus tractus solitarius (NTS), a brain nucleus with a key integrative role in homeostasis and cardiorespiratory function. Using methods and an experimental design optimized for detecting transcriptional changes less than twofold, we found 575 differentially expressed genes. We tested these genes for significant associations with physiological functions and signaling pathways using Gene Ontology terms and the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, respectively. Chronic alcohol exposure resulted in significant NTS gene regulation related to the general processes of synaptic transmission, intracellular signaling, and cation transport as well as specific neuronal functions including plasticity and seizure behavior that could be related to alcohol withdrawal symptoms. The differentially expressed genes were also significantly enriched for enzymes of lipid metabolism, glucose metabolism, oxidative phosphorylation, MAP kinase signaling, and calcium signaling pathways from KEGG. Intriguingly, many of the genes we found to be differentially expressed in the NTS are known to be involved in alcohol-induced oxidative stress and/or cell death. The study provides evidence of very extensive alterations of physiological gene expression in the NTS in the adapted state to chronic alcohol exposure.

Selectivity of pyruvate kinase for Na+ and K+ in water/dimethylsulfoxide mixtures

In aqueous media, muscle pyruvate kinase is highly selective for K+ over Na+. We now studied the selectivity of pyruvate kinase in water/dimethylsulfoxide mixtures by measuring the activation and inhibition constants of K+ and Na+, i.e. their binding to the monovalent and divalent cation binding sites of pyruvate kinase, respectively [Melchoir J.B. (1965) Biochemistry 4, 1518-1525]. In 40% dimethylsulfoxide the K0.5 app for K+ and Na+ were 190 and 64-fold lower than in water. Ki app for K+ and Na+ decreased 116 and 135-fold between 20 and 40% dimethylsulfoxide. The ratios of Ki app/K0.5 app for K+ and Na+ were 34-3.5 and 3.3-0.2, respectively. Therefore, dimethylsulfoxide favored the partition of K+ and Na+ into the monovalent and divalent cation binding sites of the enzyme. The kinetics of the enzyme at subsaturating concentrations of activators show that K+ and Mg2+ exhibit high selectivity for their respective cation binding sites, whereas when Na+ substitutes K+, Na+ and Mg2+ bind with high affinity to their incorrect sites. This is evident by the ratio of the affinities of Mg2+ and K+ for the monovalent cation binding site, which is close to 200. For Na+ and Mg2+ this ratio is approximately 20. Therefore, the data suggest that K+ induces conformational changes that prevent the binding of Mg2+ to the monovalent cation binding site. Circular dichroism spectra of the enzyme and the magnitude of the transfer and apparent binding energies of K+ and Na+ indicate that structural arrangements of the enzyme induced by dimethylsulfoxide determine the affinities of pyruvate kinase for K+ and Na+.

Dual inhibitory effects of dimethyl sulfoxide on poly(ADP-ribose) synthetase

Dimethyl sulfoxide (DMSO), a solvent popularly used for dissolving water-insoluble compounds, is a weak inhibitor of poly(ADP-ribose) synthetase, that is a nuclear enzyme producing (ADP-ribose)n from NAD+. The inhibitory mode and potency depend on the concentration of substrate, NAD+, as well as the temperature of the reaction; at micromolar concentrations of NAD+, the inhibition by DMSO is biphasic at 37 degrees C, but is monophasic and apparently competitive with NAD+ at 25 degrees C. DMSO, on the other hand, diminishes dose-dependently and markedly the inhibitory potency of benzamide and other inhibitors. Other organic solvents, ethanol and methanol, also show a biphasic effect on the synthetase activity at different concentrations.

Regulation of Na+, K(+)-ATPase by chronic ethanol exposure of PC 12 cells

The effects of chronic ethanol exposure on Na+, K(+)-ATPase were investigated in PC 12 cells. Inclusion of ethanol in the Na+, K(+)-ATPase assay (i.e. in vitro addition of ethanol) inhibited enzyme activity. Conversely, intrinsic Na+, K(+)-ATPase activity was increased after chronic ethanol exposure of the cells. This increase in Na+, K+ pumps occurred without any alteration in the inhibitory effects of in vitro ethanol. A similar response was observed when the chronic treatments were carried out using serum-free defined medium. The effects of other agents, which like ethanol decrease membrane order, were investigated. The addition of ketamine and tert-butanol in vitro caused a concentration-dependent inhibition of Na+, K(+)-ATPase activity. However, chronic exposure of the PC 12 cells to tert-butanol or ketamine did not alter either intrinsic Na+, K(+)-ATPase activity or the inhibitory effects of ethanol in vitro. Maintenance of PC 12 cells in medium containing ethanol resulted in an increase in the intracellular content of Na+ without any change in the K+ levels. In contrast, maintenance of the cells in medium containing tert-butanol did not alter intracellular levels of Na+ or K+. The present study shows that the ethanol-induced increase in Na+, K+ pumps involved an increase in the intracellular content of Na+. This increase in Na+ content did not appear to be secondary to an inhibition of Na+, K(+)-ATPase activity.

Opposite effects of dimethyl sulfoxide and ethanol on synaptic membrane fluidity

Dimethyl sulfoxide (DMSO) is an organic solvent with myriad biological actions, including actions on synaptic membrane transport processes. In this study, fluorescence polarizations of the probes diphenylhexatriene (DPH: a probe of the hydrophobic membrane core), trimethylammonium-diphenylhexatriene (a probe of the superficial domain of the cytofacial synaptic membrane leaflet) and diphenylhexatriene propionic acid (a probe of the superficial domain of the exofacial synaptic plasma membrane leaflet) were measured in isolated rat cerebral synaptic plasma membranes. DMSO, added in vitro, increased fluorescence polarization of all of these intramembranous probes, an effect opposite that observed with the addition of ethanol. The fluorescence polarization increase appeared at lower concentrations of DMSO for the superficial membrane region probes (6% vol/vol DMSO) than for the membrane core probe (10% vol/vol DMSO). This is again in contrast to the effects of ethanol, which required lesser concentrations to decrease fluorescence polarization of DPH (50 mM ethanol) than that of the derivative probes (200 mM ethanol). The enhancement of DPH fluorescence polarization produced by DMSO was antagonized by the concomitant addition of ethanol. These results suggest an ordering effect of DMSO on synaptic plasma membranes, with greater effects in superficial membrane domains.

Role of protein conformation changes and transphosphorylations in the function of Na+/K(+)-transporting adenosine triphosphatase: an attempt at an integration into the Na+/K+ pump mechanism

The particular aim of the review on some basic facets of the mechanism of Na+/K(+)-transporting ATPase (Na/K-ATPase) has been to integrate the experimental findings concerning the Na(+)- and K(+)-elicited protein conformation changes and transphosphorylations into the perspective of an allosterically regulated, phosphoryl energy transferring enzyme. This has led the authors to the following summarizing evaluations. 1. The currently dominating hypothesis on a link between protein conformation changes ('E1 in equilibrium with E2') and Na+/K+ transport (the 'Albers-Post scheme') has been constructed from a variety of partial reactions and elementary steps, which, however, do not all unequivocally support the hypothesis. 2. The Na(+)- and K(+)-elicited protein conformation changes are inducible by a variety of other ligands and modulatory factors and therefore cannot be accepted as evidence for their direct participation in effecting cation translocation. 3. There is no evidence that the 'E1 in equilibrium with E2' protein conformation changes are moving Na+ and K+ across the plasma membrane. 4. The allosterically caused ER in equilibrium with ET ('E1 in equilibrium with E2') conformer transitions and the associated cation 'occlusion' in equilibrium with 'de-occlusion' processes regulate the actual catalytic power of an enzyme ensemble. 5. A host of experimental variables determines the proportion of functionally competent ER enzyme conformers and incompetent ET conformers so that any enzyme population, even at the start of a reaction, consists of an unknown mixture of these conformers. These circumstances account for the occurrence of contradictory observations and apparent failures in their comparability. 6. The modelling of the mechanism of the Na/K-ATPase and Na+/K+ pump from the results of reductionistically designed experiments requires the careful consideration of the physiological boundary conditions. 7. Na+ and K+ ligandation of Na/K-ATPase controls the geometry and chemical reactivity of the catalytic centre in the cycle of E1 in equilibrium with E2 state conversions. This is possibly effected by hinge-bending, concerted motions of three adjacent, intracellularly exposed peptide sequences, which shape open and closed forms of the catalytic centre in lock-and-key responses. 8. The Na(+)-dependent enzyme phosphorylation with ATP and the K(+)-dependent hydrolysis of the phosphoenzyme formed are integral steps in the transport mechanism of Na/K-ATPase, but the translocations of Na+ and K+ do not occur via a phosphate-cation symport mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)

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)

Ethanol and (Na+,K+)-ATPase: alteration of Na(+)-K+ selectivity

Relative internal concentrations of Na+ and K+ are important in regulating (Na+,K+)-ATPase in situ. Ethanol is known to inhibit (Na+,K+)-ATPase and to reduce K+ affinity, but the concentrations required for these effects in vitro are large compared with those probably attainable in vivo. Yet, there is evidence suggesting that ethanol has physiologically relevant effects on (Na+,K+)-ATPase. We have investigated the effects of ethanol on selectivity for Na+ versus K+. At 150 mM, ethanol had little effect on (Na+,K+)-ATPase activity under the usual assay conditions, slightly (but nonsignificantly) reduced K+ affinity, and had no effect on extrapolated Na+ affinity in the absence of K+. However, ethanol had marked effects on cation selectivity, doubling the Ki for K+ on Na+ affinity and halving the Ki for Na+ on K+ affinity. These data show that ethanol, at concentrations too small for effects on (Na+,K+)-ATPase activity under optimal assay conditions, can alter its responses to changes in Na+ or K+.

Inhibition of (Na+, K+)-ATPase by fluoride: evidence for a membrane adaptation to ethanol

Fluoride ions inhibit several membrane enzymes in a manner that is dependent on membrane fluidity. Inhibition of (Na+, K+)-ATPase by fluoride ions may be a model for membrane effects on (Na+, K+)-ATPase. Therefore, we have examined properties of fluoride inhibition relative to interactions with ethanol and to ligands that alter sensitivity of (Na+, K+)-ATPase to ethanol. Fluoride ion reduced the K0.5 and Hill coefficient for K+ activation of p-nitrophenylphosphatase. Ethanol decreased the Hill coefficient and apparent affinity for inhibition of phosphatase activity by fluoride ion while dimethylsulfoxide had the opposite effects. Chronic ethanol treatment in vivo, which produced behavioral tolerance, had effects on fluoride inhibition opposite to those of ethanol in vitro. Inhibition by fluoride therefore may provide a useful marker for physiologic or pharmacologic conditions that alter regulation of (Na+, K+)-ATPase by membrane properties.

Ethanol may stimulate or inhibit (Na+ + K+)-ATPase, depending upon Na+ and K+ concentrations

The influence of varying the ratios of [Na+]/[K+] on the effects of alcohol (500 mg/dl) on brain (Na+ + K+)-ATPase, using a commercial porcine enzyme preparation, showed that, generally, activity was stimulated by ethanol when [Na+] less than [K+], but inhibited when [Na+] greater than [K+] (with sum kept constant at 150 mM). In addition, when [Na+]/[K+] was 15/90 mM, representative of normal intracellular levels, ethanol (500 mg/dl) stimulated the porcine enzyme, but inhibited it when [Na+]/[K+] was 144/6 mM, representative of normal extracellular levels. Similarly, in freshly prepared enzyme from highly purified rat brain synaptic membranes, ethanol (100, 300, and 450 mg/dl) stimulated when [Na+]/[K+] was 15/88 mM (representing intracellular levels), but inhibited when [Na+]/[K+] was 142/4 mM (extracellular levels).

Solvent effects on substrate and phosphate interactions with the (Na+ + K+)-ATPase

(Na+ + K+)-ATPase activity of a dog kidney enzyme preparation was markedly inhibited by 10-30% (v/v) dimethyl sulfoxide (Me2SO) and ethylene glycol (Et(OH)2); moreover, Me2SO produced a pattern of uncompetitive inhibition toward ATP. However, K+-nitrophenylphosphatase activity was stimulated by 10-20% Me2SO and Et(OH)2 but was inhibited by 30-50%. Me2SO decreased the Km for this substrate but had little effect on the Vmax below 30% (at which concentration Vmax was then reduced). Me2SO also reduced the Ki for Pi and acetyl phosphate as competitors toward nitrophenyl phosphate but increased the Ki for ATP, CTP and 2-O-methylfluorescein phosphate as competitors. Me2SO inhibited K+-acetylphosphatase activity, although it also reduced the Km for that substrate. Finally, Me2SO increased the rate of enzyme inactivation by fluoride and beryllium. These observations are interpreted in terms of the E1P to E2P transition of the reaction sequence being associated with an increased hydrophobicity of the active site, and of Me2SO mimicking such effects by decreasing water activity: (i) primarily to stabilize the covalent E2P intermediate, through differential solvation of reactants and products, and thereby inhibiting the (Na+ + K+)-ATPase reaction and acting as a dead-end inhibitor to produce the pattern of uncompetitive inhibition; inhibiting the K+-acetylphosphatase reaction that also passes through an E2P intermediate; but not inhibiting (at lower Me2SO concentrations) the K+-nitrophenylphosphatase reaction that does not pass through such an intermediate; and (ii) secondarily to favor partitioning of Pi and non-nucleotide phosphates into the hydrophobic active site, thereby decreasing the Km for nitrophenyl phosphate and acetyl phosphate, the Ki for Pi and acetyl phosphate in the K+-nitrophenylphosphatase reaction, accelerating inactivation by fluoride and beryllium acting as phosphate analogs, and, at higher concentrations, inhibiting the K+-nitrophenylphosphatase reaction by stabilizing the non-covalent E2.P intermediate of that reaction. In addition, Me2SO may decrease binding at the adenine pocket of the low-affinity substrate site, represented as an increased Ki for ATP, CTP and 3-O-methylfluorescein phosphate.

Interaction of alcohol and protein deficiency on rat brain synaptosomal (Na+-K+)-ATPase

Administration of low amounts of ethanol for a prolonged period increases rat brain synaptosomal (Na+-K+)-ATPase activity, the increase being less in the protein deficient rats. The adaptive mechanism to offset the stress imposed by the continued presence of ethanol seems to be depressed by low plane of nutrition. In vivo and in vitro effects of ethanol on (Na+-K+)ATPase seems to be different.

Effects of ethanol on rat brain (Na + K)ATPase from native and delipidized synaptic membranes

The role of lipids in the effect of ethanol on synaptosomal (Na + K)ATPase was studied using native and partially delipidized synaptosomal membranes from control and alcoholic rats. A biphasic effect of alcohol was observed with the (N + K)ATPase from control membranes. Ethanol at low concentrations (less than 100 mM) appears to enhance the enzyme activity, but at higher concentrations (greater than 300 mM) was inhibitory. The biphasic response to ethanol was also observed with the (Na + K)ATPase isolated from alcoholic animals; however, in this case the enzyme showed a resistance to the inhibitory effect of ethanol. Delipidization of synaptic membranes with Lubrol WX or phospholipase A practically abolishes the effects of alcohol on (Na + K)ATPase from both control and alcoholic animals. It thus seems that the effects of ethanol are due mainly to their interaction with the lipids surrounding the enzyme. Furthermore, addition of ethanol to native membranes did not change the Vmax and Km for K+. However, when ethanol at the same concentration was added to delipidized membranes, a decrease in Km with no change in Vmax was observed. Ethanol under these conditions apparently interacts also with the enzyme protein. On the other hand, chronic ethanol intake produces an increase of both Vmax and Km for K+. However, when alcohol was added in vitro, there were no changes in the kinetic parameters of either native or delipidized membranes. These data indicate that although the effects of ethanol on synaptosomal (Na + K)ATPase are mainly due to its interaction with the lipid microenvironment of the enzyme, a direct ethanol action on the enzyme protein also occurs. Our data further suggest that chronic ethanol treatment alters enzyme sensitivity to the effect of ethanol which may be related to the membrane-lipid composition and/or to changes in the conformation of the enzyme protein.

Effects of ethanol on ouabain inhibition of mouse brain (Na+,K+)ATPase activity

Plots of ouabain inhibition of mouse cerebral cortical (Na+,K+)ATPase activity fitted a two-site model significantly better than a one-site model, consistent with the presence of two forms of the enzyme with different affinities for ouabain. The fraction of enzyme activity with high affinity for ouabain (HAO: Ki = 500 nM), suggested to be localized neuronally, constituted the major portion (60-70%) of activity. Ouabain inhibition of both components of enzyme activity was reduced as KCl concentrations were increased. In vitro, only high concentrations of ethanol affected (Na+,K+)ATPase activity and ouabain inhibition of activity. Ethanol (500 mM) selectively reduced the activity, and increased the sensitivity to ouabain inhibition, of the HAO component, with no significant effect on the low-affinity (LAO) component. On the other hand, following chronic treatment of mice with ethanol in vivo, in a paradigm that produced tolerance and physical dependence, the sensitivity to ouabain of the HAO form of the enzyme was selectively increased. The relative proportions, and the activities of the HAO and LAO components, were not altered. The effects of ethanol, added in vitro, on the HAO component were decreased in ethanol-tolerant animals. The selective effect of chronic ethanol ingestion on (Na+,K+)ATPase activity indicates the specificity of action of ethanol in the CNS.

(Na+,K+)-ATPase and noradrenergic function: effects of chronic ethanol

The experiments in this paper examined interactions between ethanol and repeated noradrenergic stimulation in vivo on regulation of (Na+,K+)-ATPase. The increase in ouabain binding and K+-phosphatase activity associated with (Na+,K+)-ATPase in rats treated with repeated yohimbine injections was prevented by chronic ethanol. Ethanol did not affect the yohimbine-induced alterations in noradrenergic receptor binding or in content of the norepinephrine metabolite 3-methoxy-4-hydroxyphenylglycol, showing that prevention of noradrenergic stimulation of (Na+,K+)-ATPase was not caused by a decrease in availability of norepinephrine. In addition, norepinephrine depletion with the neurotoxin DSP4 did not prevent the increases in (Na+,K+)-ATPase indices during chronic ethanol treatment, showing that they did not result from increased norepinephrine exposure. These results suggest that chronic ethanol reduces sensitivity of (Na+,K+)-ATPase to norepinephrine in vivo, possibly as a consequence of membrane effects of ethanol tolerance.

Ethanol-induced inhibition of mouse brain adenosine triphosphatase activities: lack of interaction with norepinephrine in vitro

The in vitro effects of ethanol on C57BL/6J mouse forebrain ATPase activities were investigated in the presence and absence of norepinephrine. Three enzyme activities (Na + K-ATPase, Mg-ATPase, and low affinity Ca-ATPase) were studied in forebrain homogenates using a colorimetric assay. The effect of norepinephrine on ethanol inhibition of Sprague-Dawley rat brain Na + K-ATPase activity was examined in selected experiments for direct comparison with the results obtained using mouse brain. Ethanol (250-2000 mM) inhibited all ATPase activities in a concentration-dependent manner. In each case the IC50 was well beyond what would be a lethal concentration in vivo. Ethanol inhibition of mouse forebrain Na + K-ATPase activity was competitive with regards to K+ ion concentration, but was uncompetitive for inhibition of Mg-ATPase and Ca-ATPase activities. Norepinephrine (0.1 mM) did not sensitize mouse brain Na + K-ATPase activity to ethanol-induced inhibition. In contrast, norepinephrine sensitized rat brain Na + K-ATPase to ethanol inhibition when tested simultaneously with mouse brain under identical conditions. These results cannot be explained by differences in assay conditions and suggest that the interaction between norepinephrine and ethanol inhibition of Na + K-ATPase activity may be species specific. Norepinephrine alone stimulated mouse and rat brain Na + K-ATPase activity when assayed in imidazole buffer, but not when assayed in tris buffer. Furthermore, 0.1 mM norepinephrine slightly antagonized the inhibitory effect of ethanol on mouse brain Mg-ATPase activity, but did not affect ethanol-induced inhibition of Ca-ATPase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain Na+,K+-ATPase: alteration of ligand affinities and conformation by chronic ethanol and noradrenergic stimulation in vivo

These experiments examined effects of chronic ethanol, repeated noradrenergic stimulation or inhibition, and ethanol combined with the noradrenergic treatments on regulation of Na+,K+-ATPase. Chronic treatment with ethanol reduced the sensitivity of K+-p-nitrophenyl-phosphatase to ethanol, increased affinity for K+, reduced the sensitivity of K+ affinity to ATP or ethanol, and reduced delta H and delta S for K+ activation and for the E1-E2 transition. These effects were all opposite to those of ethanol added in vitro. Treatment with yohimbine had the opposite effects on ethanol sensitivity, K+ affinity, K+ interactions with ethanol and ATP, and thermodynamic parameters for cation activation or conformational change. These effects were similar to those of norepinephrine in vitro. The effects of yohimbine treatment were eliminated or reduced in rats also treated with ethanol. Depletion of norepinephrine had effects opposite to those of yohimbine. These data are consistent with a reduction in membrane fluidity, at least in the vicinity of Na+,K+-ATPase, during ethanol tolerance. Exposure to norepinephrine, in vitro or in vivo, had effects on Na+,K+-ATPase that were similar to those of increased membrane fluidity.

Effects of short-chain alcohols and norepinephrine on brain (Na+,K+)ATPase activity

(Na+,K+)ATPase activity in synaptic membranes from whole brains of mice was inhibited by a series of short-chain aliphatic alcohols (ethanol through pentanol). The relationship of inhibitory potency to alcohol chain length and to alcohol membrane:water partition coefficient suggested that the inhibitory effect of the alcohols does not depend totally on their interaction with neuronal membrane lipids. Although partitioning into the membranes is important for this inhibitory effect, a direct interaction of alcohol with the enzyme protein may also be involved in the inhibition. Norepinephrine did not significantly potentiate inhibition of (Na+,K+)ATPase activity by low concentrations of ethanol in preparations of either mouse or rat brain. Thus, under our conditions, ethanol, at levels which can be reached in vivo, only slightly inhibited enzyme activity, and the possible importance of this inhibition in mediating the in vivo acute or chronic effects of ethanol on the CNS remains open to question.

The Hofmeister effect and the behaviour of water at interfaces

Starting from known properties of non-specific salt effects on the surface tension at an air-water interface, we propose the first general, detailed qualitative molecular mechanism for the origins of ion-specific (Hofmeister) effects on the surface potential difference at an air-water interface; this mechanism suggests a simple model for the behaviour of water at all interfaces (including water-solute interfaces), regardless of whether the non-aqueous component is neutral or charged, polar or non-polar. Specifically, water near an isolated interface is conceptually divided into three layers, each layer being I water-molecule thick. We propose that the solute determines the behaviour of the adjacent first interfacial water layer (I1); that the bulk solution determines the behaviour of the third interfacial water layer (I3), and that both I1 and I3 compete for hydrogen-bonding interactions with the intervening water layer (I2), which can be thought of as a transition layer. The model requires that a polar kosmotrope (polar water-structure maker) interact with I1 more strongly than would bulk water in its place; that a chaotrope (water-structure breaker) interact with I1 somewhat less strongly than would bulk water in its place; and that a non-polar kosmotrope (non-polar water-structure maker) interact with I1 much less strongly than would bulk water in its place. We introduce two simple new postulates to describe the behaviour of I1 water molecules in aqueous solution. The first, the 'relative competition' postulate, states that an I1 water molecule, in maximizing its free energy (--delta G), will favour those of its highly directional polar (hydrogen-bonding) interactions with its immediate neighbours for which the maximum pairwise enthalpy of interaction (--delta H) is greatest; that is, it will favour the strongest interactions. We describe such behaviour as 'compliant', since an I1 water molecule will continually adjust its position to maximize these strong interactions. Its behaviour towards its remaining immediate neighbours, with whom it interacts relatively weakly (but still favourably), we describe as 'recalcitrant', since it will be unable to adjust its position to maximize simultaneously these interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

The synthesis and secretion of gastric mucus glycoprotein by mucosal cells cultured in the presence of ethanol

The effect of ethanol on the synthesis and secretion of mucus glycoprotein in gastric mucosal cells was investigated. The mucosal cell suspensions were subjected to a short-term (4 h) culture in the presence of 0-1.5 M ethanol, with [3H]proline and [3H]palmitic acid as markers for glycoprotein synthesis and acylation. The synthesized labeled mucus glycoprotein was isolated from the incubation medium (extracellular glycoprotein) and from the mucosal cells (intracellular glycoprotein), and analyzed. Depending upon the ethanol concentration in the cell culture medium, two distinct effects on the synthesis and secretion of mucus glycoprotein were observed. The cells cultured in the presence of 0.02-0.1 M ethanol showed increased ability for the incorporation of [3H]proline and [3H]palmitic acid, and for the secretion of the newly assembled mucus glycoprotein. The synthesis of the glycoprotein increased 18-fold, acylation 5-fold, and secretion 10-fold. The synthesized glycoprotein, however, contained four to five times less of acyl-bound fatty acids. Ethanol at 0.1-1.5 M caused a marked reduction (62-64%) in the mucus glycoprotein synthesis, but the amount of glycoprotein released to the medium remained constant. This indicated that higher concentrations of ethanol caused the release of the preformed intracellular mucus glycoprotein reserves. The results demonstrate that gastric mucosal cells incubated in the presence of ethanol exhibit impaired synthesis and secretion of mucus glycoprotein, and that the severity of impairment depends upon the ethanol concentration.

Free fatty acids and (Na+,K+)-ATPase: effects on cation regulation, enzyme conformation, and interactions with ethanol

Effects of free fatty acids on parameters of (Na+,K+)-ATPase regulation related to enzyme conformation were examined. Sensitivity to inhibition by free fatty acid increased as the number of double bonds increased. Free fatty acids reduced affinity for K+ or Na+ at their regulatory sites without altering apparent K+ affinity at its high-affinity site, and increased apparent affinity for ATP. The apparent E2/E1 ratio and apparent delta H and delta S for the E1-E2 transition were reduced by fatty acid. High K+ or low temperature reduced the sensitivity of enzyme to inhibition by free fatty acid. In the presence of low K+, arachidonic acid potentiated inhibition of phosphatase activity by ethanol. Arachidonic acid alone had little effect on the rate of ouabain binding, but accelerated ouabain binding in the presence of K+. These data suggest that fatty acids alter (Na+,K+)-ATPase by preventing the univalent cation-mediated transition to E2, the K+-sensitive form of enzyme. (Na+,K+)-ATPase could potentially be influenced in vivo by free fatty acids released by phospholipases or during hypoxia, or by changes in membrane lipid saturation.