Ethanol stimulates shape change in human platelets by activation of phosphoinositide-specific phospholipase C

Protein changes during ethanol induced seed germination in Aconitum heterophyllum

Aconitum heterophyllum is a high altitude medicinal plant that has become endangered due to overexploitation for their aconitins. The most effective, conventional propagation method for any plant species is by seed. However, in Aconitum seed germination is erratic, and seedling survival is low. In the present study results have been discussed on the possible implication of ethanol treatment on removal of barriers on radical emergence in terms of protein changes. Eighty seven percent of seed germination was achieved in Aconitum with ethanol treatment. Comparative 2-DE analysis of ethanol treated and untreated seed protein profiles in Phase II of germination revealed 40 differentially expressed proteins. Twenty-seven out of 40 proteins were induced, 5 were increased and 8 were repressed. Mass spectrometry and subsequent identification confirmed that these proteins were involved in metabolism, DNA regulation, stress tolerance and plasmamembrane/cell wall biosynthesis/extension processes. These protein changes might be responsible for physiological and physical changes, respectively, resulted in increase in germination percentage. Further, characterization of these proteins will be of great help in understanding the molecular mechanism lying behind enhanced germination in response to ethanol treatment.

Inhibition of PAR4 Signaling Mediates Ethanol-Induced Attenuation of Platelet Function In Vitro

BACKGROUND

Reduction in coronary heart disease morbidity in response to moderate consumption of alcoholic beverages may be partly mediated by ethanol-induced inhibition of platelet function. However, the precise mechanisms by which ethanol modulates platelet activation induced by thrombin, which plays a central role in hemostasis, remain unclear. The goal of this study was to investigate ethanol-induced changes in platelet function and clarify the underlying mechanisms including PAR1 and PAR4 activity and [Ca2+]i dynamics in vitro.

METHODS

Platelet aggregation, increase in intracellular calcium ([Ca2+]i), and release of platelet factor 4 and beta-thromboglobulin induced by alpha-thrombin, PAR1-agonist peptide (AP), or PAR4-AP were assessed in the presence or absence of ethanol.

RESULTS

Ethanol exposure inhibited low-dose thrombin (0.5 nM)-induced aggregation but not an increase in [Ca2+]i. In contrast, ethanol had no effect on high-dose thrombin (10 nM)-induced aggregation or the [Ca2+]i increase. Ethanol did not significantly inhibit thrombin-induced release of platelet factor 4 and beta-thromboglobulin. Ethanol reduced PAR1-AP-induced aggregation, but did not affect the spike form of [Ca2+]i increase. In contrast, ethanol inhibited the increase in [Ca2+]i as well as the aggregation in response to PAR4-AP and resulted in delayed [Ca2+]i peak time. Furthermore, ethanol inhibited both PAR1-AP- and PAR4-AP-induced platelet factor 4 and beta-thromboglobulin release.

CONCLUSIONS

These data suggest that ethanol inhibits platelet aggregation via inhibition of PAR4 signaling and subsequent inhibition of Ca2+ influx and granule release. This phenomenon may contribute to the reduction in coronary heart disease morbidity in response to consumption of alcoholic beverages.

Effects of alcohol on hemostasis

Several epidemiologic studies have shown that moderate intake of alcohol is associated with a lower risk of cardiovascular disease (CVD), but the mechanism is not fully elucidated. One of the proposed mechanisms of the protective effect of moderate alcohol intake is its beneficial effect on hemostasis. The aim of this review is to summarize the effect of ethanol intake on platelet aggregation and activation, coagulation factors including von Willebrand factor (vWF), and the fibrinolytic system. With regard to the effect of alcohol on platelet function, evidence in the literature suggests both platelet activation and platelet inhibition by ethanol. A unifying hypothesis is that platelets are partially activated by ethanol, with partial degranulation allowing for continued circulation of platelets with impaired function. Evidence also exists showing that ethanol intake decreases fibrinogen, factor VII, and vWF levels. In addition, alcohol intake has been found to increase fibrinolysis by increasing tissue plasminogen activator activity. The effect of ethanol on platelets, coagulation factors, and the fibrinolytic system is likely to contribute to protection against CVD.

Effect of low doses of ethanol on platelet function in long-life abstainers and moderate-wine drinkers

In vitro, high concentrations of ethanol (EtOH) reduce platelet aggregation. Less is known about the effect of low EtOH doses on platelet function in a selected human population of long-life abstainers and low moderate-wine drinkers to avoid rebound effect of EtOH on platelet aggregation. Results of our experiments suggest that moderate-wine drinkers have higher levels of high density lipoprotein (HDL) than long-life abstainers while fibrinogen levels are unchanged. Furthermore, platelets obtained from these individuals do not differ in their response when stimulated by agonists such as AA and collagen. The effect of in vitro exposure of low doses of EtOH has been studied in PRP and in washed platelets. EtOH (0.1-10 mM) inhibits platelet aggregation induced by collagen at its ED50 while is ineffective when aggregation was triggered by U-46619 and by 1 microM adenosine diphosphate (ADP). 5-10 mM EtOH partially reduces the second wave of aggregation induced by 3 microM ADP. 0.1-10 mM EtOH dose-dependently lowers the aggregation induced by AA at its ED50 but it is less effective at ED75 of AA. The antiaggregating effect of EtOH on aggregation induced by AA is unchanged by inhibitor of nitric oxide synthase. In addition, 10 mM EtOH reduces thromboxane (Tx) formation. In washed platelets, 1-10 mM EtOH partially inhibits platelet aggregation induced by thrombin. In washed resting platelets, 10 mM EtOH does not change the resting [Ca++]i while significantly reduces the increase in [Ca++]i triggered by AA. The results of ex vivo experiments have demonstrated that wine increases the HDL. However, this observation may or may not influence the response of platelets to agonists. Results of our studies demonstrate that low doses of alcohol reduces platelet function.

Molecular modelling of specific and non-specific anaesthetic interactions

There has been rapid progress in molecular modelling in recent years. The convergence of improved software for molecular mechanics and dynamics, techniques for chimeric substitution and site-directed mutations, and the first x-ray structures of transmembrane ion channels have made it possible to build and test models of anaesthetic binding sites. These models have served as guides for site-directed mutagenesis and as starting points for understanding the molecular dynamics of anaesthetic-site interactions. Ligand-gated ion channels are targets for inhaled anaesthetics and alcohols in the central nervous system. The inhibitory strychnine-sensitive glycine and gamma-aminobutyric acid type A receptors are positively modulated by anaesthetics and alcohols; site-directed mutagenesis techniques have identified amino acid residues important for the action of volatile anaesthetics and alcohols in these receptors. Key questions are whether these amino acid mutations form part of alcohol- or anaesthetic-binding sites or if they alter protein stability in a way that allows anaesthetic molecules to act remotely by non-specific mechanisms. It is likely that molecular modelling will play a major role in answering these questions.

Staurosporine and H7 attenuate ethanol-induced elevation in [Ca2+]i in cultured canine cerebral vascular smooth muscle cells

Chronic exposure of cultured canine cerebral vascular smooth muscle cells to ethanol (10-400 mM) for 1-5 days resulted in significant concentration-dependent elevation in resting intracellular free calcium ([Ca2+]i) levels. Preincubation of these cultured vascular cells with inhibitors of protein kinase C (PKC), staurosporine and H7, induced no apparent changes from the control resting levels of [Ca2+]i. However, the increases of [Ca2+]i due to ethanol treatment were attenuated markedly by staurosporine and H7. Our data suggest that activation of PKC plays an important role in ethanol's action in producing a sustained rise in [Ca2+]i in cerebral vascular smooth muscle cells. Activation of PKC could thus play a crucial role in the pathogenesis of alcohol-induced cerebral ischemia and stroke.

Intracellular mechanisms of constriction of rat aorta by ethanol

The intracellular mechanisms mediating vasoconstriction by ethanol are poorly understood. This investigation was designed to provide evidence on the role of protein kinase C (PKC) and calmodulin in vasoconstriction by ethanol. We studied helically cut strips of rat aorta that were exposed to ethanol before and in the presence of the PKC inhibitors calphostin C (79, 239, and 798 nM) or 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7, 10 microM), and the calmodulin inhibitor, trifluoperazine (TFP, 10 microM). To test for the specificity of the PKC inhibitors, we measured the responses of aortas to potassium and phorbol 12-myristate 13-acetate (PMA) in the absence and presence of calphostin C and H7. To test for the specificity of TFP, we measured the responses of aortas to serotonin, potassium, PMA, and the thromboxane A2 mimic. 9,11-dideoxy-11 alpha, 9 alpha-epoxy-methanoprostaglandin F2a (U46619), in the absence and presence of TFP. We also studied the effect of the combination of calphostin C and TFP on constriction of the aorta by ethanol. We also measured the importance of intracellular and extracellular calcium in constriction of the aorta by ethanol. Force generation was measured before, and then during exposure of the strips to calcium-free buffer with EGTA, or calcium-free buffer with EGTA plus caffeine. We found that both PKC inhibitors antagonized vasoconstriction by ethanol and PMA. However, H7 antagonized contractions by potassium, but calphostin C did not. We found that TFP caused 99 +/- 1% inhibition of maximum contraction to serotonin, 90 +/- 4% inhibition of maximum contraction to potassium, 63 +/- 6% inhibition of maximum contraction to PMA, and 8 +/- 5% inhibition of maximum contraction to U46619. TFP caused a 22 +/- 8% inhibition of contraction to ethanol. The combination of TFP and calphostin C antagonized vasoconstriction by ethanol to a degree similar to that of calphostin C alone. We also found that contractions to ethanol were only 16 +/- 7% of control values in a calcium-free plus EGTA buffer. Contractions to ethanol were 0 +/- 1% of control values in calcium-free buffer with EGTA plus caffeine. We conclude that: 1-vasoconstriction by ethanol is, at least in part, mediated by PKC; 2-constriction by ethanol is mediated to a minimal extent by calmodulin, and 3-part of the constriction by ethanol of the aorta is mediated by a caffeine-sensitive pool of intracellular calcium.

Effect of administered ethanol on protein kinase C in human platelets

There are numerous reports of the effect of ethanol on protein kinase C (PKC) in animals or with in vitro systems. However, the effect of ethanol on PKC in humans has not been extensively investigated despite the large number of studies involving PKC and human platelets. In this study, we administered ethanol to human volunteers and determined the level of PKC before and after a 0.4 g/kg dose of ethanol. We studied Native Americans and Caucasians of both sexes. There was an increases in PKC activity 60 min after ethanol administration. There were no ethnic, age, nor gender differences detected, nor was there any correlation between family history of alcoholism and the basal or stimulated platelet PKC levels. Neither was there any correlation of basal or stimulated PKC activity with the genotypes for ADH2, ADH3, ALDH2, CYP2E1, and CYP1A2.

Wines and grape juices as modulators of platelet aggregation in healthy human subjects

To test the hypothesis that red wine, by virtue of its relatively high concentration of polyphenols, is more protective against atherosclerosis and coronary heart disease (CHD) than white wine, and that grape juice enriched in one of these, trans-resveratrol, may share some of these properties, studies were performed on 24 healthy males aged 26-45 years. Each consumed the following beverages for periods of 4 weeks: red wine, white wine, commercial grape juice and the same grape juice enriched with trans-resveratrol. Apart from the last beverage, 2 weeks abstinence was maintained before commencing the schedule. Blood was taken at the beginning and end of each schedule to determine plasma thromboxane B2 (TxB2) concentration and the IC50 (concentration required for 50% aggregation) for ADP and thrombin-induced platelet aggregation. White wine (P < 0.05) but not red wine increased the IC50 for ADP. Both wines increased the IC50 for thrombin (P < 0.02 and P < 0.001, respectively) and also lowered plasma TxB2 concentrations (P < 0.01 and P < 0.025, respectively). Neither grape juice altered ADP-induced aggregation or TxB2 concentrations, but the commercial juice lowered the IC50 for thrombin (P < 0.001) whereas the resveratrol-enriched juice caused a dramatic increase (P < 0.001). In vitro experiments demonstrated that the aggregation of fresh washed human platelets by ADP and thrombin was moderately reduced by both grape juices, strongly by red wine and not at all by white wine. The synthesis of TxB2 by platelets from labelled arachidonate was stimulated by commercial grape juice, slightly enhanced by resveratrol-enriched juice and strongly inhibited by red wine with white wine having little effect. Platelets from subjects consuming the commercial juice had a higher ratio of cyclo-oxygenase to lipoxygenase product formation and those consuming the resveratrol-enriched juice a lower ratio than during the control period. We conclude that trans-resveratrol can be absorbed from grape juice in biologically active quantities and in amounts that are likely to cause reduction in the risk of atherosclerosis. The failure of red wines (which have a 20-fold excess of polyphenols over white wines) to show any advantage suggests that, in vivo, ethanol is the dominant anti-aggregatory component in these beverages which are more potent than grape juices in preventing platelet aggregation in humans.

Different pathways of in vitro ethanol-induced apoptosis in thymocytes and splenic T and B lymphocytes

To investigate the intracellular pathways leading to ETOH-induced apoptosis, thymocytes and splenic T and B cells were cultured 16 h with or without ETOH and different stimuli, and apoptotic cell death was determined. At concentrations of 0.4%-2% in culture, ETOH induced apoptosis in all three types of cells, but it had a more profound effect on thymocytes and B cells as compared with its effect on T cells. In thymocytes, ETOH-induced apoptosis was abrogated by chelation of extracellular calcium with EGTA, and inhibition of protein synthesis with CHX, or of PKC with H7 but not of PKA with HA 1004. ETOH potentiated the apoptosis of thymocytes induced with the calcium ionophore A23187 and suboptimal doses of PMA, but it had negligible effect on dAMP- and PGE2-induced apoptosis of thymocytes. In contrast to findings in thymocytes, the ETOH-induced apoptosis of T and B cells was almost completely abrogated by PMA, but not by H7 or CHX. In spleen cells, calcium chelation with EGTA triggered apoptosis. ETOH significantly inhibited EGTA-induced apoptosis of B cells but had little effect on EGTA-induced apoptosis of T cells. IL-4 reduced the ETOH-induced apoptosis of B and T cells, but it was not effective in the prevention of apoptosis of thymocytes. Inhibition of the calcium-dependent neutral protease calpain I did not rescue cells from apoptosis. Moreover, treatment with CI-I potentiated ETOH-induced apoptosis in T cells. These results suggest that both thymocytes and splenic T and B cells have relevant apoptotic pathways that can be induced by ETOH, but the mechanisms of ETOH-induced apoptosis differ in these cells.

Inhibitory effect of alcohol on cyclic GMP accumulation in human platelets

The effects of ethanol on cyclic GMP (cGMP) in washed human platelets were studied in the presence and absence of sodium nitroprusside (SNP), nitric oxide donor which stimulates guanylate cyclase. SNP stimulated cGMP accumulation in a dose-dependent fashion. After 1 min exposure to 100 microM SNP, the level of cGMP was approximately four-fold that in vehicle-treated platelets. Alcohol had no effect on basal cGMP, but inhibited SNP-induced cGMP accumulation at 17, 85 and 170 mM. In further experiments, platelets were incubated for 0, 0.5, 1 2 or 5 min with 10 microM SNP, with or without 100 microM zaprinast, a selective cGMP-phosphodiesterase (PDE) inhibitor and 85 mM ethanol. In the presence of zaprinast but not alcohol, cGMP levels rose continuously, to 10-fold the basal level at 5 min. Without zaprinast, cGMP levels were lower and reached a plateau by 2 min. Accumulation of cGMP was attenuated by alcohol 2 and 5 min after SNP addition, both in zaprinast-treated platelets and those without zaprinast. Thus, alcohol inhibits platelet cGMP accumulation stimulated by nitric oxide donor. Its mechanism probably does not involve a major effect on PDE, because the inhibition was observed in the presence or absence of zaprinast. We hypothesize that alcohol inhibits guanylate cyclase, contributing to its complex functional effects in platelets.

Alcohol and platelet function

Epidemiological studies have shown that moderate consumption of alcoholic beverages is inversely related to the incidence of the complications of coronary artery disease. The protective effect of ethanol may be partially attributable to an inhibitory effect of ethanol on platelets. This article summarizes the experimental observations that ethanol inhibits platelet responses to specific physiological agonists. In alcoholics, various platelet defects have been observed, but these may be influenced by metabolic factors rather than the presence of ethanol alone. The acute effects of ethanol on platelet functions both in vivo and ex vivo will be reviewed. Evidence will be presented demonstrating that ethanol added acutely in vitro inhibits phospholipase A2 in stimulated platelets. The interaction of ethanol with other signal transduction pathways will also be discussed.

Organic Solvents Activate Human Platelets Through the Inositol Lipid-linked Signal Transduction System

It has recently been proposed that occupational exposure to organic solvents in vivo may lead to platelet activation and this has been substantiated by exposure of platelets to solvents in vitro. The present work was undertaken to study the effects of organic solvents on the platelet inositol lipid signal transduction system. Human platelets that had been prelabelled with [(32)P] P, were exposed to a saturated atmosphere of the organic solvents toluene, xylene or hexane. Extracts were analyzed for metabolites of the polyphosphoinositide cycle and ATP. All solvents studied induced a decrease in radioactivity in phosphatidylinositol 4,5-bisphosphate together with an increase in radioactivities in phosphatidylinositol 4-phosphate and phosphatidic acid. This is compatible with solvent-induced activation of the cells through the inositol lipid pathway. In cells exposed to toluene or xylene we could detect an increased level in inositol trisphosphates at 3 min of exposure. The solvent-induced changes in metabolic ATP could not explain the solvent-induced effects on the inositol lipid metabolism. It is concluded that the organic solvents toluene, xylene and hexane can activate human platelets through the inositol lipid-linked transmembrane signal system.

Ethanol exposure increases total protein kinase C activity in human lymphocytes

Human circulating lymphocytes were isolated and incubated with ethanol. Cytosolic, membrane-bound and total detergent extractable protein kinase C (PKC) activities were measured. Exposure to ethanol (100 mm) resulted in an increase in PKC activity, with membrane-associated PKC activity increasing with respect to cytosolic activity at 5 min of exposure. Higher concentrations of ethanol up to 200 mm were associated with increases in total detergent extractable PKC activity. Ethanol was the most potent of a series of straight chain alcohols studied for their effects on detergent-extractable PKC activity.

Cooperative effects of ethanol and protein kinase C activators on phospholipase-D-mediated hydrolysis of phosphatidylethanolamine in NIH 3T3 fibroblasts

In a previous study, ethanol was shown to enhance the stimulatory effect of phorbol 12-myristate 13-acetate (PMA), a prominent activator of protein kinase C (PKC), on phospholipase-D (PLD)-mediated hydrolysis of phosphatidylethanolamine (PtdEtn) in NIH 3T3 fibroblasts (Kiss et al. (1991) Eur. J. Biochem. 197, 785-790). Here, the mechanism and possible significance of ethanol-stimulated PtdEtn hydrolysis was further studied. In [14C]ethanolamine-labeled NIH 3T3 fibroblasts, 10 mM ethanol enhanced PMA-induced hydrolysis of PtdEtn 1.5-2.0-fold during a 2.5-15-min incubation period. Other alcohols, including glycerol, methanol, and 1-propanol, also enhanced PMA-induced PtdEtn hydrolysis. Of the other PLD activators tested, ethanol potentiated the PKC-dependent stimulatory effect of bombesin but failed to alter the apparently PKC-independent stimulatory effect of serum. Pretreatment of [14C]ethanolamine-labeled fibroblasts with 200 mM ethanol for 20 min resulted in increased (approx. 2-fold) hydrolysis of [14C]PtdEtn in isolated membranes. In membranes from ethanol-treated, but not from untreated, cells, PMA further enhanced (approx. 1.5-fold) the production of [14C]ethanolamine. Ethanol exerted none of the above stimulatory effects on phosphatidylcholine hydrolysis. These results suggest that the specific stimulatory action of ethanol on PLD-mediated PtdEtn hydrolysis can occur in vivo and may involve increased binding of a regulatory PKC-isoform to membranes.

The long-term combined stimulatory effects of ethanol and phorbol ester on phosphatidylethanolamine hydrolysis are mediated by a phospholipase C and prevented by overexpressed alpha-protein kinase C in fibroblasts

The protein kinase C (PKC) activator 12-O-tetradecanoylphorbol 13-acetate (TPA) has been shown to potentiate the stimulatory effect of ethanol on the hydrolysis of phosphatidylethanolamine (PtdEtn) in NIH 3T3 fibroblasts. Following an initial 20-min period, the main product of PtdEtn degradation in cells treated with TPA plus ethanol was ethanolamine phosphate. Here, we have examined the regulatory role of PKC and the possible catalytic role of phospholipase C in the formation of ethanolamine phosphate. TPA, bryostatin, and bombesin, direct or indirect activators of PKC, had similar potentiating effects on ethanol-induced formation of [14C]ethanolamine phosphate from [14C]PtdEtn in [14C]ethanolamine-prelabelled NIH 3T3 fibroblasts. At lower concentrations of ethanol (40-80 mM), significant stimulation of ethanolamine phosphate formation required longer treatments (2 h or longer). The combined effects of TPA (100 nM) and ethanol (50-200 mM) on ethanolamine phosphate formation were not inhibited by the PKC inhibitors staurosporine or 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7). In contrast, these inhibitors significantly inhibited TPA-induced formation of ethanolamine, catalyzed by a phospholipase-D-type enzyme. In membranes isolated from TPA+ethanol-treated cells, enhanced formation of ethanolamine phosphate was maintained for at least 20 min. Down-regulation of PKC by prolonged (24-h) treatment of NIH 3T3 fibroblasts by 300 nM TPA enhanced, while overexpression of alpha-PKC in Balb/c fibroblasts diminished, the stimulatory effect of ethanol on the formation of ethanolamine phosphate. Finally, addition of the protein phosphatase inhibitor okadaic acid (2 microM) to fibroblasts inhibited TPA+ethanol-induced formation of ethanolamine phosphate. These results suggest that alpha-PKC-mediated protein phosphorylation may negatively regulate PtdEtn hydrolysis and that the potentiating effect of TPA may result, at least partly, from increased degradation of this PKC isoform.

Ethanol exposure results in a transient decrease in human platelet cAMP levels: evidence for a protein kinase C mediated process

At concentrations between 2 and 32 mM, ethanol is shown to depress human platelet cAMP levels. The effect is biphasic, maximal at 30 sec, with platelet concentrations of cAMP returning to baseline values at higher ethanol concentrations and at longer incubation times. The cAMP lowering effect of ethanol can be blocked by a phosphodiesterase (PPDE) inhibitor, 3-isobutyl-1-methyl-xanthine (IBMX), at a concentration of 2 mM, suggesting that an increase in PPDE activity may be responsible for this effect. Exposure of platelets to 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7), a protein kinase C (PKC) inhibitor, blocks the ethanol-induced decrease in platelet cAMP, suggesting ethanol may be acting through activation of PKC.

Mechanism of ethanol-induced aggregation in whole blood

Effects of ethanol on blood clotting and platelet aggregation have been reported in many models, but its in vitro actions in whole blood, impedance aggregometry have not been reported. We investigated the effect of ethanol in vitro in whole blood and platelet rich plasma of humans and rats, as measured by impedance aggregometry. Ethanol (34 to 170 mM) induced concentration-dependent aggregation in whole blood but not platelet rich plasma. In further studies in rats, aggregation was inhibited by pretreatment of whole blood with the prostacyclin analog iloprost or the enzyme apyrase, which degrades ADP to AMP. Levels of ethanol which produced aggregation in whole blood were also associated with concentration-dependent hemolysis. Based on the requirement for whole blood for ethanol-induced aggregation, the inhibitory effect of apyrase and our observation of hemolysis, and previous studies which have demonstrated the potential contribution of ADP from lysed red blood cells to platelet aggregation, we conclude that ethanol-induced aggregation in whole blood is mediated by erythrocyte lysis and the ADP released from these cells.

Effect of chronic ethanol treatment and selective breeding for sensitivity to ethanol on calcium release induced by inositol trisphosphate or ethanol from brain and liver microsomes

Our previous work showed that ethanol increases the resting intracellular free calcium concentration (CAi) in synaptosomes and releases calcium from an inositol trisphosphate (IP3)-insensitive calcium store of brain microsomes. In this report, we investigated the effects of chronic ethanol treatment and selective breeding for hypnotic sensitivity to ethanol on IP3 and ethanol-stimulated calcium release from brain and liver microsomes. Chronic ethanol treatment did not alter IP3-stimulated calcium release from brain microsomes or ethanol-stimulated calcium release from brain or liver microsomes. Chronic ethanol treatment increased the spontaneous release of calcium from brain but not liver microsomes. In microsomes isolated from cerebellum or cerebral cortex of long-sleep (LS) and short-sleep (SS) mice, ethanol and IP3 released calcium in a concentration dependent manner. The amount of calcium released by ethanol and IP3 was larger in microsomes isolated from cerebellum than microsomes from cerebral cortex. However, the amount of calcium released by ethanol and IP3 did not differ between the two lines in either brain area. These results do not support the idea that the hypnotic effects of ethanol are due to ethanol-induced calcium release from a nonmitochondrial intracellular calcium store in brain tissue. The development of ethanol tolerance and dependence also does not appear to be associated with altered ability of ethanol to release calcium from non-mitochondrial intracellular stores; however, effects of chronic ethanol exposure on spontaneous release of intracellular calcium could alter neuronal function in ethanol dependence.

Phospholipase C activation by ethanol in rat hepatocytes is unaffected by chronic ethanol feeding

The activation of phosphoinositide-specific phospholipase C by ethanol was compared in hepatocytes isolated from ethanol-fed rats and from pair-fed control animals. Ethanol (100-300 mM) caused a dose-dependent transient increase in cytosolic free Ca2+ levels in indo-1-loaded hepatocytes from both groups of animals. The rate of Ca2+ increase was similar in hepatocytes from control and ethanol-fed rats, but the decay of the Ca2+ increase was somewhat slower in the latter preparation. The ethanol-induced Ca2+ increase caused activation of glycogen phosphorylase, with 50% response at 50 mM-ethanol and a maximal response at 150-200 mM-ethanol, not significantly different in hepatocytes from control and ethanol-fed animals. Ins(1,4,5)P3 formation in response to ethanol (300 mM) or vasopressin (2 nM or 40 nM) was also similar in the two preparations. It is concluded that long-term ethanol feeding does not lead to an adaptive response with respect to the ethanol-induced phospholipase C activation in rat hepatocytes. The ability of ethanol in vitro to decrease membrane molecular order in liver plasma membranes from ethanol-fed and control rats was measured by e.s.r. Membranes from ethanol-fed animals had a significantly lower baseline order parameter compared with control preparations (0.313 and 0.327 respectively), indicative of decreased membrane molecular order. Addition of 100 mM-ethanol significantly decreased the order parameter in control preparations by 2.1%, but had no effect on the order parameter of plasma membranes from ethanol-fed rats, indicating that the plasma membranes had developed tolerance to ethanol, similar to other membranes in the liver. Thus the membrane structural changes associated with this membrane tolerance do not modify the ethanol-induced activation of phospholipase C. The transient activation of phospholipase C by ethanol in hepatocytes may play a role in maintaining an adaptive phenotype in rat liver.

Effect of guanine nucleotides on polyphosphoinositide synthesis in rat liver plasma membranes

The effect of guanosine 5'-[gamma-thio]triphosphate (GTP[S]) on PtdIns and PtdIns(4)P kinase activities was measured in rat liver plasma membranes. The addition of [32P]ATP resulted in the rapid incorporation of 32P into PtdIns(4)P and PtdIns(4,5)P2, with maximal levels reached within 30 s. GTP[S] (25-500 microM) increased the rate and magnitude of [32P]PtdIns(4)P and [32P]PtdIns(4,5)P2 formation by 50 and 120% respectively. Similar stimulatory effects were induced by guanosine 5'-[beta gamma-imido]triphosphate, GTP, GDP and guanosine 5'-[beta-thio]diphosphate. The stimulation of PtdIns phosphorylation by GTP[S] occurred in the presence of 2 mM-EGTA, a condition which fully inhibited phosphoinositide-specific phospholipase C. GTP[S] did not stimulate phosphomonoesterase activity, and its action was not due to the binding of magnesium. However, the overall ATP-hydrolysing activity of the membrane preparation was inhibited by GTP[S] and the other guanine nucleotides. There was a direct correlation between the extent of this inhibition and the stimulation of polyphosphoinositide formation. The results indicate that stimulation of polyphosphoinositide formation by guanine nucleotides in rat liver plasma membranes can be accounted for by an inhibition of ATP hydrolysis. These data are inconsistent with a specific GTP-binding protein (G-protein)-mediated stimulation of PtdIns or PtdIns(4)P kinase.

Protein kinase C participates in up-regulation of dihydropyridine-sensitive calcium channels by ethanol

Exposure to ethanol for several days increases the expression of dihydropyridine-sensitive, voltage-dependent Ca2+ channels in brain and in the neural cell line PC12. Since protein phosphorylation is a major mechanism by which ion channels are regulated, we used protein kinase inhibitors to investigate whether ethanol-induced up-regulation of Ca2+ channels involves activation of a protein kinase. Sphingosine and polymixin B, which inhibit protein kinase C and calmodulin-dependent kinases, prevented the enhancement of 45Ca2+ uptake induced by exposure of PC12 cells to ethanol for 4 days. In addition, sphingosine blocked the ability of ethanol to increase the number of [3H]dihydropyridine binding sites in PC12 cell membranes. Sphingosine's effect was prevented by simultaneous exposure to phorbol 12,13-dibutyrate, a potent activator of protein kinase C. Therefore, protein kinase C appears to be involved in the up-regulation of dihydropyridine-sensitive Ca2+ channels during prolonged exposure to ethanol.

Ethanol inhibits thrombin-induced secretion by human platelets at a site distinct from phospholipase C or protein kinase C

Ethanol is known to inhibit the activation of platelets in response to several physiological agonists, but the mechanism of this action is unclear. The addition of physiologically relevant concentrations of ethanol (25-150 mM) to suspensions of washed human platelets resulted in the inhibition of thrombin-induced secretion of 5-hydroxy[14C]tryptamine. Indomethacin was included in the incubation buffer to prevent feedback amplification by arachidonic acid metabolites. Ethanol had no effect on the activation of phospholipase C by thrombin, as determined by the formation of inositol phosphates and the mobilization of intracellular Ca2+. Moreover, ethanol did not interfere with the thrombin-induced formation of diacylglycerol or phosphatidic acid. Stimulation of platelets with phorbol ester (5-50 nM) resulted in 5-hydroxy[14C]tryptamine release comparable with those with threshold doses of thrombin. However, ethanol did not inhibit phorbol-ester-induced secretion. Ethanol also did not interfere with thrombin- or phorbol-ester-induced phosphorylation of myosin light chain (20 kDa) or a 47 kDa protein, a known substrate for protein kinase C. By electron microscopy, ethanol had no effect on thrombin-induced shape change and pseudopod formation, but prevented granule centralization and fusion. The results indicate that ethanol does not inhibit platelet secretion by interfering with the activation of phosphoinositide-specific phospholipase C or protein kinase C by thrombin. Rather, the data demonstrate an inhibition of a Ca2(+)-mediated event such as granule centralization.

Inhibition of ethanol-induced platelet activation by agents that elevate cAMP

Ethanol activates phosphoinositide-specific phospholipase C in human platelets resulting in the mobilization of intracellular calcium and shape change (Arch. Biochem. Biophys. 260, 480-492, 1988). Preincubation of platelets with agents that increase levels of cAMP (i.e., forskolin, prostacyclin) inhibited these responses to ethanol in a concentration- and time-dependent manner. The inhibitory effect was potentiated by the phosphodiesterase inhibitor, isomethybutylxanthine. When added after ethanol, these agents also reversed platelet shape change and lowered cytosolic free calcium to basal levels. The results demonstrate a direct inhibitory effect of cAMP on the ethanol-induced activation of phospholipase C.

Calcium-dependent chloride currents elicited by injection of ethanol into Xenopus oocytes

Electrophysiological techniques were used to study the response of native Xenopus laevis oocytes to intracellular injection and bath application of ethanol. Injection of ethanol produced dose-dependent transient inward currents accompanied by large current fluctuations, with estimated intracellular concentrations ranging from 10 to 300 mM. The response duration varied between 2 and 15 min, with an onset delay of 2-15 s. The inward current sometimes consisted of a fast and a slow component. Bath application of equivalent concentrations elicited similar but considerably smaller responses. The current showed a reversal potential of -20 +/- 10 mV, corresponding to an increase in chloride permeability. The response was eliminated in the presence of low chloride saline and was blocked by the chloride channel inhibitors SITS and DIDS. Ethanol responses were inhibited by the intracellular injection of the calcium chelator EGTA and were unaffected when the extracellular calcium was lowered. It is concluded that ethanol injection into Xenopus oocytes elicits a release of calcium from intracellular stores, which then activates an increased membrane permeability to chloride.

Ethanol stimulates basal and serotonin-induced formation of [32P]phosphatidic acid in human platelets

The addition of serotonin to preparations of 32P-labelled human platelets resulted in a time- and dose-dependent hydrolysis of [32P]phosphatidylinositol 4,5-bisphosphate (PIP2) and formation of [32P]phosphatidic acid (PA). This response was inhibited by the serotonin2 receptor antagonist ritanserin, indicating that the stimulation was mediated via the serotonin2 receptor. The addition of 50-150 mM of ethanol prior to stimulation with 10(-5) M serotonin resulted in an increased accumulation of [32P]PA, but had no effect on [32P]PIP2. Ethanol stimulated [32P]PA formation at all serotonin concentrations studied (10(-7)-10(-5) M). Furthermore, in the absence of serotonin, ethanol increased basal [32P]PA formation.

Ethanol interferes with collagen-induced platelet activation by inhibition of arachidonic acid mobilization

The effect of ethanol on signal generation in collagen-stimulated human platelets was evaluated. Incubation of washed human platelets with physiologically relevant concentrations of ethanol (25-150 mM) resulted in a dose-dependent inhibition of aggregation and secretion in response to collagen (0.5-10 micrograms/ml), but did not inhibit shape change. In platelets labeled with [3H]arachidonic acid, ethanol significantly inhibited the release of arachidonic acid from phospholipids, in both the presence and the absence of indomethacin. Thromboxane B2 formation was also inhibited in proportion to the reduction in free arachidonic acid. There was a close correlation between the extent of inhibition of arachidonic acid release and secretion. The inhibition of platelet aggregation and secretion by ethanol was partially overcome by the addition of exogenous arachidonic acid. In the presence of indomethacin, ethanol had no effect on the activation of phospholipase C by collagen as determined by the formation of inositol phosphates and phosphatidic acid. Moreover, ethanol had no effect on the mobilization of intracellular calcium by collagen and only minimally inhibited the early phases of the phosphorylation of myosin light chain (20 kDa) and a 47-kDa protein, a known substrate for protein kinase C. Arachidonic acid formation was also inhibited by ethanol in response to ionomycin under conditions where phospholipase C activation was prevented. The results suggest that the functional effects of ethanol on collagen-stimulated platelets are due, at least in part, to an inhibition of phospholipase A2.

Alcohol-induced stimulation of phospholipase C in human platelets requires G-protein activation

In previous studies we have demonstrated that ethanol activates hormone-sensitive phospholipase C in intact human platelets, resulting in the mobilization of intracellular Ca2+ and platelet shape change. The present study aims to localize further this effect of ethanol by examining its interaction with the regulation of phospholipase C in a permeabilized cell system. In platelets permeabilized with a minimal concentration (18 micrograms/ml) of saponin, ethanol by itself did not activate phospholipase C. However, ethanol potentiated the activation of phospholipase C in response to the non-hydrolysable GTP analogue GTP[S] (guanosine 5'-[gamma-thio]triphosphate), an effect similar to that observed with thrombin. Ethanol also potentiated the response to fluoride, which acts directly on G-proteins. Other short-chain alcohols also stimulated phospholipase C in a synergistic manner with GTP[S]. The ability of specific alcohols to stimulate phospholipase C was directly related to their respective lipid-solubilities, as determined by their partition coefficients. Moreover, the potencies of each alcohol correlated with their ability to elicit Ca2+ mobilization and shape change in intact platelets. These effects of ethanol were eliminated by a disruption of receptor-phospholipase C coupling induced by the addition of higher concentrations of saponin. These data indicate that the activation of phospholipase C by ethanol may occur by affecting protein-protein interactions in the signal-transduction complex involving GTP-binding regulatory proteins.