Brain synaptosomal (Na+ and K+)ATPase activity as an index of tolerance to ethanol

Effect of exogenous melatonin on ethanol-induced changes in Na(+),K(+)- and Ca(2+)-ATPase activities in rat synaptosomes

In the present study, the effects of acute ethanol (EtOH) toxicity and of exogenous melatonin (MLT) on this toxicity were examined by measuring membrane-bound ATPases and acetylcholinesterase activities in rat synaptosomal membranes. The concentrations of plasma alpha-tocopherol and adrenal ascorbic acid (AA) were also measured. Synaptosomal Na(+),K(+)-ATPase and Ca(2+)-ATPase activities were significantly depressed in acute EtOH-intoxicated rats compared with controls, while acetylcholinesterase activity remained unaltered. Pretreatment with MLT (10 mg/kg) prior to acute EtOH administration prevented EtOH-induced inhibition of ATPases. Adrenal AA and plasma alpha-tocopherol levels were also depressed regardless of MLT pretreatment. MLT treatment alone affected neither membrane-bound enzyme activities nor tissue and blood levels of vitamins C and E. It is concluded that acute EtOH intoxication disturbs neural transport functions through the membrane-bound ATPase activity depression. Reduced AA and alpha-tocopherol levels may contribute to the neurodegenerative effects of EtOH. However, pretreatment with a high dose of MLT before EtOH administration may be beneficial to prevent EtOH-induced toxicity on ATPase-mediated neural transport functions.

Enhanced (Na+K)-ATPase activity and expression in mouse brain after chronic ethanol administration

It is the general hypothesis that the primary mode of action of ethanol is the alteration of membrane structure and function including the conformation of receptors and ion channels essential for neurotransmission and signal transduction. However, the issue of whether ethanol affects (Na+K)-ATPase under physiological conditions remains unsettled. In this study, adult mice were treated with a daily dose of 5 g/kg of ethanol for 28 days. The RNA was isolated from brain and the (Na+K)-ATPase mRNA level was determined using Northern blot analysis. We have found an increased expression of (Na+K)-ATPase alpha-subunit in the chronically treated alcohol group as compared with that of controls. This result was further substantiated by increased protein phosphorylation as well as increased specific activity of this enzyme in the synaptosomal plasma membrane after chronic ethanol administration. Thus we have demonstrated that ethanol may directly affect (Na+K)-ATPase in vivo, leading to the increased synthesis of this enzyme through adaptive mechanisms.

Effects of in vitro ethanol on the brain cation pump in alcoholics and controls

In vivo ethanol exposure reduces in vitro Na+,K(+)-adenosine triphosphatase (Na+,K(+)-ATPase) sensitivity to ethanol in some animal models, but very little is known about the effects of ethanol on human brain Na+,K(+)-ATPase. Cerebral cortex homogenates from 13 male alcoholic and 9 control subjects were assayed for K(+)-p-nitrophenylphosphatase (K(+)-pNPPase, a measure of Na+,K(+)-ATPase) and Mg(2+)-pNPPase activities at 37 degrees for 20 min in 75 mM imidazole-HCl (pH 7.4), 5 mM p-nitrophenylphosphate, 5 mM MgCl2, and 20 mM KCl, with or without 1 mM ouabain. Native K(+)-pNPPase activites were similar in control and alcoholic brains (61.5 +/- 3.5 vs 55.3 +/- 3.1 nmol/mg/min). In vitro exposure to a near lethal ethanol level (0.5%, or 110 mM) was without effect, whereas 5% ethanol inhibited K(+)-pNPPase activity by about 28% (P < 0.001) in both groups. Both 0.5 and 5% ethanol in vitro significantly stimulated Mg(2+)-pNPPase activity (1-2% and 19-20%, respectively). By comparison, mouse brain K(+)-pNPPase was inhibited significantly by in vitro ethanol, and Mg(2+)-pNPPase activity was unaffected. Ethanol levels attainable in humans may not be sufficient to alter significantly brain Na+,K(+)-ATPase activity.

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.

Interactive effects of dietary (n-3) polyunsaturated fatty acids and chronic ethanol intoxication on synaptic membrane lipid composition and fluidity in rats

The influence of dietary polyunsaturated fatty acids on fatty acid composition, cholesterol and phospholipid content as well as 'fluidity' (assessed by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) probes) of brain synaptic plasma membranes (SPM) and their interactions with chronic ethanol effects were studied in rats fed for two generations with diets either devoid of (n-3) fatty acids (sunflower oil diet), rich in alpha-linolenic acid (soya oil diet) or in long chain (n-3) fatty acids (sunflower + cod liver oil diet). Results were compared with rats fed standard lab chow. Sunflower oil led to an increase in the (n-6)/(n-3) ratio in the membranes with an increase of the 'fluidity' at membrane apolar level; sunflower + cod liver oil decreased the (n-6)/(n-3) ratio without affecting membrane 'fluidity' while no difference was seen between the SPM of rats fed soya oil and standard diet. After 3 weeks alcohol intoxication in rat fed the standard diet: oleic alpha-linoleic acids and cholesterol levels were increased, arachidonic acid and the double bond index/saturated fatty acids were decreased and there was a decrease of 'fluidity' in the lipid core of the SPM. Soya oil almost totally abolished these usually observed changes in the SPM fatty acids composition but increased oleic acid and cholesterol without any change in fluidity. Sunflower oil led to the same general alterations of fatty acid as seen with standard diet but to a greater extent, with decrease of the 'fluidity" at the apolar level and in the region probed by TMA-DPH. When sunflower oil was supplemented with cod liver oil, oleic and alpha-linoleic acids were increased while the 'fluidity' of the apolar core of SPM was decreased. So, the small changes in fatty acid pattern seem able to modulate neural properties i.e. the responses to a neurotoxic like ethanol. A structurally specific role of PUFA is demonstrated by the pernicious effects of the alpha-linolenic acid deficient diet which are not totally prevented by the supply of long chain (n-3) PUFA.

[Biophysical membrane correlates of tolerance and dependence on alcohol]

A large number of studies have given clear indications that ethanol does affect the physicochemical properties of the membrane. Membrane reorganization and adaptation can develop against the acute disordering effect of ethanol during chronic intoxication. Nevertheless, there has been so far no direct evidence of correlations between functional tolerance or dependence and membrane physical states. Membrane physical state can be assessed by fluorescence polarization of DPH in the absence (measure of membrane 'fluidity') or presence (measured of membrane sensitivity) of ethanol added in vitro. Functional tolerance has been already correlated with a reduced synaptic membrane sensitivity to ethanol (membrane tolerance). Behavioural dependence was shown to be quantifiable by measurement of alcohol intake in a free choice situation (water/alcohol) solution). This dependence model allowed us to define a membrane dependence which consists in an increased membrane rigidity (or decrease in 'fluidity') persistent after withdrawal, and which was correlated to the intensity of the behavioural dependence. This biophysical expression of dependence seems rather independent of the biophysical membrane tolerance (resistance to the acute ethanol fluidizing effect), which was found to be rapidly reversible after withdrawal and re-induced by alcohol re-intake, requiring recent periods of current abuse to be expected.

Differential response of adenylate cyclase and ATPase activities after chronic ethanol exposure of PC12 cells

The direct effects of chronic ethanol administration on adenylate cyclase, Na,K-ATPase, and Mg-ATPase activities in a cell containing neuronal characteristics were investigated using PC12 pheochromocytoma cells. Exposure of PC12 cells to 0, 75, and 150 mM ethanol for 4 days caused a dose-dependent increase in the stimulation of adenylate cyclase by in vitro ethanol without altering activation of the enzyme by GTP, NaF, MnCl2, or 2-chloroadenosine. Conversely, a 4-day treatment with 150 mM ethanol increased Na,K-ATPase and Mg-ATPase activities without altering the inhibitory effects of in vitro ethanol. The increase in Na,K-ATPase activity was associated with an increase in Vmax without any change in the Km for KCl. Chronic ethanol exposure also increased the amount of [3H]ouabain specifically bound to PC12 cell membranes. Except for the increase in Mg-ATPase activity, the above results were also observed when chronic ethanol treatment was carried out in the presence of pyrazole. Although ethanol slowed PC12 cell growth, observed changes were not due to an ethanol-induced reduction in cellular density. A 4-day exposure of a nonneuronal cell line (Madin Darby canine kidney cell) to 150 mM ethanol did not alter adenylate cyclase or ATPase activities. The present study indicates that the direct effects of chronic ethanol exposure of a neuronal-like cell involve an increase in the density of sodium pumps per cell and an enhanced sensitivity of adenylate cyclase to activation by ethanol.

Alcohol-induced alterations in phosphoinositide hydrolysis in astrocytes

Cultured astrocytes exposed to ethanol were prelabeled with [3H]inositol and the accumulation of [3H]inositol phosphates was determined following stimulation with norepinephrine (NE). Acute doses of alcohol (25-200 mM) had little effect on phosphoinositide (PI) hydrolysis. However, chronic exposure for 7 days produced significant increases in hydrolysis with ethanol concentrations as low as 50 mM. The onset of alcohol-induced increases occurred within 4 hr of exposure, reaching maximum values by Days 3 to 5. Withdrawal resulted in the return of stimulated PI hydrolysis to pre-alcohol exposure levels after 2 days. The evidence provided suggests that chronic exposure of ethanol alters the alpha-adrenergic receptor characteristics of astrocytes and/or enhances the effector pathway leading to PI hydrolysis at a site distal to the receptor.

2,4-D-n-butyl ester (2,4-D ester) induced ataxia in rats: role for n-butanol formation

Three formulations of 2,4-D were tested in rats for their ability to increase landing foot splay, a measure of ataxia. When administered for three to four consecutive days, 2,4-D-n-butyl ester (150 mg/kg/day SC) produced significant increases in landing foot splay while 2,4-D acid (120 mg/kg/day SC) and 2,4-D mixed butyl esters (150 mg/kg/day SC) did not. The ability of acute n-butanol, 2-butanol, and a 50:50 mixture of both (2.13 mM/kg SC) to increase landing foot splay was then assessed. Only n-butanol significantly increased landing foot splay. Similarly, when n-butanol was administered daily, at doses corresponding to 150 mg/kg/day of the 2,4-D-n-butyl ester, significant increases in landing foot splay were evident. The pattern of splay increases was remarkably similar to that observed for 2,4-D-n-butyl ester. When locomotor activity was the dependent variable, daily n-butanol had no effect. These results suggest that in vivo formation of n-butanol after administration of 2,4-D-n-butyl ester is responsible for the motor incoordination but not the depression of locomotor activity observed following 2,4-D-n-butyl ester administration. These data demonstrate that different formulations of the same herbicide can produce differential behavioral effects.

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)

Membrane fluidity and alcohol dependence

Rats were chronically intoxicated with alcohol by exposing them to increasing concentrations of ethanol vapor over a 4-week period. They were tested for alcohol consumption in a free choice situation of water and 10% (v/v) alcohol. On the basis of their intakes they were divided into alcohol-dependent and nondependent groups. Synaptosome membrane fluidity evaluated by fluorescence polarization was compared between the two groups and against nonintoxicated controls. The intoxicated animals had a lower membrane fluidity than controls, mainly because of a highly significant increase of rigidity in the alcohol-dependent group. Furthermore, membrane fluidity was found to be correlated with the degree of behavioral dependence (i.e., alcohol intake during the free choice period).

Abnormal fluidity and surface carbohydrate content of the erythrocyte membrane in alcoholic patients

Erythrocyte membranes from 11 healthy individuals and 11 alcoholic patients, examined within 24 hr of withdrawal, were studied for membrane fluidity as assessed by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene and for the concentrations of sialic acid and galactose in the membrane surface. Basal fluorescence polarization was significantly higher in the alcoholics and the membranes were clearly more resistant to the fluidizing effect of ethanol added in vitro. The concentrations of sialic acid as well as galactose were significantly reduced in the patients. The increased resistance to the fluidizing effect of ethanol added in vitro appeared to be functionally related to reduced concentrations of terminal sialic acid and terminal and sialic acid-bound beta-galactose in the membrane surface. The increased basal rigidity is probably due to concomitant changes in the lipid bilayer of the membrane. The results also showed, for the first time, that similar perturbations of membrane fluidity occur in human alcoholics as have been found previously in chronically ethanol-treated animals.

Ethanol and membrane lipids

Although ethanol is known to exert its primary mode of action on the central nervous system, the exact molecular interaction underlying the behavioral and physiological manifestations of alcohol intoxication has not been elucidated. Chronic ethanol administration results in changes in organ functions. These changes are reflective of the adaptive mechanisms in response to the acute effects of ethanol. Biophysical studies have shown that ethanol in vitro disorders the membrane and perturbs the fine structural arrangement of the membrane lipids. In the chronic state, these membranes develop resistance to the disordering effects. Tolerance development is also accompanied by biochemical changes. Although ethanol-induced changes in membrane lipids have been implicated in both biophysical and biochemical studies, measurements of membrane lipids, such as cholesterol content, fatty acid unsaturation, phospholipid distribution, and ganglioside profiles, have not produced conclusive evidence that any of these parameters are directly involved in the action of ethanol. On the other hand, there is increasing evidence indicating that although ethanol in vitro produces a membrane-fluidizing effect, the chronic response to this effect is not to change the membrane bulk lipid composition. Instead, changes in membrane lipids may pertain to small metabolically active pools located in certain subcellular fractions. Most likely, these lipids are involved in important membrane functions. For example, the increase in PS in brain plasma membranes may provide an explanation for the adaptive increase in synaptic membrane ion transport activity, especially (Na,K)-ATPase. There is also evidence that the lipid pool involved in the deacylation-reacylation mechanism (i.e., PI and PC with 20:4 groups) is altered after ethanol administration. An increase in metabolic turnover of these phospholipid pools may have important implications for the membrane functional changes. Obviously, there are other lipid-metabolizing enzyme systems that may exert similar effects but have not yet been investigated in detail. From the results of these studies, it is concluded that the multiple actions of ethanol are associated with changes in enzymic systems important in the functional expression of the membranes.

Changes in (Na+ + K+) ATPase activity and the composition of surface carbohydrates in erythrocyte membranes in alcoholics

(Na+ + K+)ATPase activity and sensitivity to the inhibitory effect of ethanol and noradrenaline in vitro as well as the concentrations of sialic acid, galactose, and hexosamine were determined in erythrocyte membranes in 20 healthy controls and in 20 alcoholic patients within 24 hr of withdrawal. Basal (Na+ + K+)ATPase activity, the sensitivity of the enzyme to inhibition by ethanol and noradrenaline added in vitro, and the concentrations of sialic acid and galactose were significantly reduced in the patients (p less than 0.0005). All of these abnormalities were significantly correlated to each other as well as to the estimated daily quantity of ethanol consumed. After enzymatic removal of terminal sialic acid and terminal and sialic acid-bound beta-galactose, the (Na+ + K+)ATPase differences between the patients and the controls were eliminated. The results showed that the previously reported reduced inhibition of (Na+ + K+)ATPase by ethanol in the presence of noradrenaline in brain membranes in chronically ethanol-fed animals is also found in erythrocyte membranes in alcoholic humans. Abnormal carbohydrate composition of glycolipids and/or glycoproteins of the membrane surface appeared to be related to the (Na+ + K+)ATPase changes, possibly due to interference either with K+ transport or surface electrostatics or, directly or indirectly, with the conformation of (Na+ + K+)ATPase.

Brain membrane sensitivity to ethanol during development of functional tolerance to ethanol in rats

Adult male rats were rendered progressively tolerant to ethanol by daily intragastric administration of doses of 3-6 g/kg body weight. Functional tolerance assessed by the hypothermic effect after injection of a challenge dose of ethanol developed slowly and was demonstrable after 2 weeks of treatment. Intrinsic crude synaptosomal membrane fluidity, as assessed by fluorescence polarization of DPH, as well as (Na+ + K+)ATPase activity, did not change significantly during the whole treatment. However, the extra addition of ethanol (0.175-0.700 M) in vitro to the membranes of rats, having received ethanol over a period of at least 2 weeks, fluidized less and inhibited the (Na+ + K+)ATPase activity less than in starch-fed controls. The time-course for the appearance of this membrane hyposensitivity was found to be the same as the time course for the development of functional tolerance to ethanol. The correlation between the degree of functional tolerance and the (Na+ + K+)ATPase sensitivity to ethanol appeared very significant, highlighting the sensitivity of membrane-bound enzymes to detecting adaptive changes in complex biological membranes tolerance.