Perturbation of membrane fluidity

Effect of dietary fatty acids on metabolic rate and nonshivering thermogenesis in golden hamsters

Hibernating rodents prior to winter tend to select food rich in polyunsaturated fatty acids (PUFA). Several studies found that such diet may positively affect their winter energy budget by enhancing torpor episodes. However, the effect of composition of dietary fatty acids (FA) on metabolism of normothermic heterotherms is poorly understood. Thus we tested whether diets different in FA composition affect metabolic rate (MR) and the capacity for nonshivering thermogenesis (NST) in normothermic golden hamsters (Mesocricetus auratus). Animals were housed in outdoor enclosures from May 2010 to April 2011 and fed a diet enriched with PUFA (i.e., standard food supplemented weekly with sunflower and flax seeds) or with saturated and monounsaturated fatty acids (SFA/MUFA, standard food supplemented with mealworms). Since diet rich in PUFA results in lower MR in hibernating animals, we predicted that PUFA-rich diet would have similar effect on MR of normothermic hamsters, that is, normothermic hamsters on the PUFA diet would have lower metabolic rate in cold and higher NST capacity than hamsters supplemented with SFA/MUFA. Indeed, in winter resting metabolic rate (RMR) below the lower critical temperature was higher and NST capacity was lower in SFA/MUFA-supplemented animals than in PUFA-supplemented ones. These results suggest that the increased capacity for NST in PUFA-supplemented hamsters enables them lower RMR below the lower critical temperature of the thermoneural zone.

Diet affects resting, but not basal metabolic rate of normothermic Siberian hamsters acclimated to winter

We examined the effect of different dietary supplements on seasonal changes in body mass (m(b)), metabolic rate (MR) and nonshivering thermogenesis (NST) capacity in normothermic Siberian hamsters housed under semi-natural conditions. Once a week standard hamster food was supplemented with either sunflower and flax seeds, rich in polyunsaturated fatty acids (FA), or mealworms, rich in saturated and monounsaturated FA. We found that neither of these dietary supplements affected the hamsters' normal winter decrease in m(b) and fat content nor their basal MR or NST capacity. NST capacity of summer-acclimated hamsters was lower than that of winter-acclimated ones. The composition of total body fat reflected the fat composition of the dietary supplements. Resting MR below the lower critical temperature of the hamsters, and their total serum cholesterol concentration were lower in hamsters fed a diet supplemented with mealworms than in hamsters fed a diet supplemented with seeds. These results indicate that in mealworm-fed hamsters energy expenditure in the cold is lower than in animals eating a seed-supplemented diet, and that the degree of FA unsaturation of diet affects energetics of heterotherms, not only during torpor, but also during normothermy.

Structural and functional modifications induced by ketamine on synaptosomes in the rat

This study correlates previous observations on the effects of a general anaesthetic (2-chlorophenyl-2-methylaminocyclohexanone, trade name Ketalar), administered in vivo on the functional properties of synaptosomes from the brain of the rat, with structural modifications detected using freeze-fracture electron microscopy. The anaesthetized rats exhibited a fluidization of the synaptic membranes, as probed by stearic acid spin labels, accompanied by a decrease in the activity of acetylcholinesterase. The freeze-fracture images of synaptosomes from anaesthetized rats showed a clear statistical increase in the number of vesicles with aggregated intramembrane particles, without any significant change of the particle diameter. The hypothesis that a perturbation of the lipid protein interaction is a primary effect, in the mechanism of action of anaesthetics, is supported at present only by indirect evidence.

Evaluation of antiepileptic drug effect on membrane fluidity

Many drugs and chemicals have been shown to induce modifications of the physicochemical properties of cellular membranes. In this study we investigated the changes in fluidity of erythrocyte membrane from epileptic patients under different pharmacological treatments, with respect to healthy controls, by using trimethylammonium-1,6-diphenyl-1,3,5-hexatriene (TMA-DPH) fluorescence polarization. The increase in TMA-DPH fluorescence polarization values observed in epileptic patients indicated a decrease in membrane fluidity. Since the analysis of erythrocyte membrane composition did not reveal significant differences between the two groups studied, a correlation with membrane lipoperoxide content was tried, as different drugs and chemicals elicit in vivo alterations resulting in peroxidation of membrane lipids. Therefore the presence of peroxidation products in the blood and the possible correlation with membrane lipoperoxide were studied. Although a direct causal linkage cannot be proved we can hypothesize that exogenous compounds such as antiepileptic drugs could modify membrane fluidity by increasing membrane lipid peroxidation. Moreover the increase of peroxidative products in the blood could indicate that the peroxidative damage might propagate through the formation of new free radical species. The possibility of using erythrocyte membrane as a model system to analyze antiepileptic drug side effects is advanced.

Effects of ethanol on VIP-and/or noradrenaline-stimulated cAMP formation in mouse brain

Among several effects, ethanol (EtOH) interferes with membrane fluidity and lipid-protein interactions. As proteins are influenced by surrounding lipids, the activity of membrane-bound enzymes such as adenylate cyclase (AC) could be modulated by EtOH, as shown in potentiating, at toxic concentrations, the stimulating effect of hormones or neurotransmitters. We have also found that EtOH potentiates in a dose-dependent manner (EC50 = 100 mM) the cAMP production elicited by vasoactive intestinal peptide (VIP), already noticeably at 70 mM, without affecting basal cAMP levels (up to 400 mM). Propanol produces a similar potentiation, whereas methanol was inactive. Butanol (200 mM) displays toxic effects. The potentiation induced by EtOH is similar for peptide- (VIP) or monoamine- (noradrenaline) stimulated cAMP formation, suggesting a primary action at a interaction between VIP and NA in stimulating cAMP formation.

Critical temperatures for the interaction of free fatty acids with the erythrocyte membrane

Non-esterified long-chain fatty acids reduce the extent of hypotonic hemolysis at a certain low concentration range but cause hemolysis at higher concentrations. This biphasic behavior was investigated at different temperatures (0-37 degrees C) for lauric (12:0), myristic (14:0), palmitoleic (16:1), oleic (cis-18:1) and elaidic (trans-18:1) acids. The results are summarized as follows: (A) the fatty acids examined exhibit a high degree of specificity in their thermotropic behavior; (B) oleic acid protects against hypotonic hemolysis even at the highest concentrations, up to 15 degrees C, when it becomes hemolytic, but only in a limited concentration range; (C) elaidic acid does not affect the osmotic stability of erythrocytes up to 20 degrees C, when it starts protecting: above 30 degrees C, it becomes hemolytic at the highest concentrations; (D) palmitoleic acid is an excellent protecting agent at all temperatures in a certain concentration range, becoming hemolytic at higher concentrations; (E) lauric acid protects up to 30 degrees C and becomes hemolytic only above this temperature; (F) myristic acid exhibits an extremely unusual behavior at 30 and 37 degrees C by having alternating concentration ranges of protecting and hemolytic effects; (G) there is a common critical temperature for hemolysis at 30 degrees C for saturated and trans-unsaturated fatty acids; (H) the initial slope of Arrhenius plots of percent hemolysis at the concentration of maximum protection is negative for cis-unsaturated fatty acids and positive for saturated and trans-unsaturated fatty acids.

Phosphatidylcholine and phosphatidylethanolamine derivatives, membrane fluidity and changes in the lipolytic activity of ram spermatozoa plasma membranes during cryoconservation

1. A decrease of the alkenyl-acyl derivatives and an increase of the diacyl derivatives of PC and PE were observed after cryoconservation. 2. A diminution of membrane-bound phospholipase A2 activity was observed after cryoconservation. The activity of neutral sphingomyelinase remained unchanged. 3. The enrichment of plasma membranes with DPPC as well as the addition of the cryoprotector of Nagase-Niwa were observed to protect the membranes from fluidization.

Effects of some alcohols on the conformation of mitochondrial H+-ATPase complex and F1-ATPase from pig heart

The conformations of the H+-ATPase complex and F1-ATPase in low concentrations of methanol, ethanol, n-propanol, iso-propanol and t-butanol were studied by circular dichroism. For F1-ATPase, all but methanol first increased and then decreased the circular dichroism magnitude of helical bands as the alcohol concentration was increased. With ethanol, n-propanol, iso-propanol and t-butanol, the alpha-helix content reached a maximum at about 5% alcohol and began to decrease at 10%. The content of beta-sheet showed the opposite effect, reaching a minimum at 5% and increasing slightly at higher concentrations. None of the alcohols studied had a significant effect on the conformation of the H+-ATPase complex. This difference implies that the alcohols had a greater effect on free F1-ATPase than on the membrane-bound F1-ATPase. The hydrophobic protein F0 and the membrane lipids in the H+-ATPase complex may stabilize and protect F1 from the effects of the alcohols.

Binding of [14C] DDT by submitochondrial particles

1. Binding of [14C] DDT by submitochondrial particles and by liposomes prepared from lipids extracted from the particles was studied by the discontinuous sucrose gradient method. 2. Binding of the insecticide was a biphasic linear function of the biomembrane- and liposome-concentration with a break in the binding curve occurring at identical concentrations of phospholipid for both the biomembrane and vesicle. The biphasic binding curve is interpreted in terms of decreased availability of binding sites as a result of particle-particle interaction. 3. [14C] DDT was bound mainly by the membrane lipids and only negligible binding was detected for the delipidated membrane. 4. A 100-200-fold excess of unlabeled DDT had no effect on the binding of [14C] DDT and a 600-fold excess of unlabeled DDT reduced the binding by 20% suggesting that binding of [14C] DDT by lipids was nonspecific. 5. These results are discussed in relation to the strong inhibition by DDT of mitochondrial bioenergetics.

Enzymatic reconstitution of brain membrane and membrane opiate receptors

A new method using lysophosphatide and acyl-CoA as detergents has been used to solubilize the rat brain opiate receptor. After solubilization, lysophosphatide and acyl-CoA can be almost completely removed by an enzymatic reaction that uses an acyltransferase from rat liver microsomes and reconstitutes the solubilized receptor in membranous vesicles. Morphological studies performed with negative staining and freeze-fracture electron microscopy revealed that the general appearance and intramembrane particle distribution of fracture faces in the reconstituted membrane are similar to those of the native membrane; this indicates that hydrophobic protein components of the original membrane were incorporated during reconstitution. Reconstituted membrane, however, contained higher levels of phosphatidylcholine and lower levels of cholesterol. The activities of the membrane-bound enzymes Na+, K+-ATPase and Ca2+, Mg2+-ATPase in the reconstituted system were 24 and 3%, respectively, those of the native membrane. Although binding of opiate ligands to the reconstituted membrane was stereospecific and saturable, higher concentrations of some of the unlabeled ligands were required to inhibit binding of the radiolabeled ligands. These changes in receptor characteristics are likely due to changes in lipid composition, physical state, and/or distribution of the lipids in the reconstituted membrane bilayer. This conclusion is supported by an increase in the affinity of opiate ligands for reconstituted membrane after adjustment of the latter's lipid composition to match more closely that of the original membrane. This was accomplished by treatment with phospholipid exchange protein to remove the excess phosphatidylcholine and by incorporation of cholesterol into the reconstituted membrane.

Ethanol's effects on cortical adenylate cyclase activity

The effects of ethanol on beta-adrenergic receptor-coupled adenylate cyclase (AC) of mouse cerebral cortex were examined. The addition of ethanol (20-500 mM) to incubation mixtures containing cortical membranes demonstrated that ethanol could increase AC activity and potentiate the stimulatory effects of guanylyl-imidodiphosphate [Gpp(NH)p] on AC activity. Ethanol increased the rate of activation of AC by guanine nucleotides and concomitantly decreased the EC50 for magnesium required to achieve maximal stimulation of cortical AC. The EC50 values for Gpp(NH)p and isoproterenol stimulation of AC activity were also altered by ethanol. Ethanol was capable of stimulating AC extracted by use of digitonin. The AC activity in the digitonin extract was no longer sensitive to the addition of Gpp(NH)p or NaF, but was still stimulated by ethanol. We propose multiple sites of action for ethanol in stimulating cortical AC activity. These sites include actions at the beta-adrenergic receptor, at the G/F coupling proteins, and at the catalytic unit of cortical AC. Comparison of ethanol's actions on cortical beta receptor coupled AC activity with prior reported actions of ethanol on striatal dopamine (DA)-sensitive AC indicated differential sensitivities of these two AC systems to ethanol. These differences may be determined by specific coupling characteristics of the striatal and cortical AC systems or by differences in the plasma membranes in which striatal and cortical AC systems are located.

Chronic ethanol exposure alters dopaminergic signal transduction processes

A number of data suggest that the chronic ethanol treatment induces derangements of cell membrane structure leading to modifications of membrane related processes. In particular, alterations have been observed in the mechanisms of neurotransmitter recognition and in the coupling of the receptor with the effector system. Phosphorylation of specific proteins by cyclic AMP stimulated protein kinases represent the final step in the biological response in several distinct functional processes. Ethanol neurotoxic action therefore may affect neurotransmitter availability and release as well as receptors effector systems and protein phosphorylation. In this line, chronic ethanol treatment in rats decreases cyclic AMP dependent protein kinase activity in rat striatal membrane fractions. When lysine rich histone type III was used as exogenous substrate, cyclic AMP stimulated 32P incorporation was still decreased in the ethanol group. These data favor the hypothesis of a decreased capability of the enzyme to phosphorylate in response to cAMP.

Age related differences in dopamine-stimulated adenylate cyclase sensitivity to "in vivo" chronic ethanol treatment

The effect of chronic ethanol consumption on adenylate cyclase activity was measured in striatal membranes derived from aged male rats. The results indicate that the cyclic AMP generating system of old rats has a different sensitivity to ethanol effect compared to the adult animals. In young animals the basal adenylate cyclase activity was enhanced by alcohol consumption while the DA stimulated cyclic AMP production was reduced. In contrast, in 24 months old rats ethanol reduced the basal adenylyl cyclase and enhanced the response to DA indicating a supersensitivity of adenylate cyclase linked DA receptors. This observation was further supported by 3H-Spiperone binding studies. In fact, a higher Bmax was measured in striatal membranes of aged ethanol-dependent rats in comparison to control.

Effects of ammonia on synaptosomal membranes

Acute and sustained hyperammonemia in mice resulted in a decrease of the transition temperature of Arrhenium plots of synaptosomal (Na+-K+)ATPase. The activation energies in both phases of the plots were increased. "In vitro" addition of ammonia produced similar changes. This seems to indicate that ammonia alters the physical properties of synaptosomal membranes. The "in vitro" interaction of ammonia and ethanol at the membrane level was also investigated. Both agents together produced a further shift in the transition temperature and affected the activation energies. The relevance of these findings regarding the mechanism of ammonia toxicity and the protective effect of ethanol thereon is discussed.

Effect of temperature on kinetics of hexose uptake by human placental plasma membrane vesicles

Initial rates of passive and carrier-mediated D-galactose and D-glucose uptake were measured in membrane vesicles derived from the maternal surface of the human placental syncytiotrophoblast. Passive diffusion, as measured by L-glucose uptake, was slightly and continuously temperature-sensitive over a range 0-40 degrees C (Q10 = 1.1). Below approx. 26 degrees C, passive diffusion measured by D-galactose uptake in the presence of the inhibitor, cytochalasin B, was quantitatively similar to L-glucose uptake. Above this temperature, however, cytochalasin B appeared not to be as effective an inhibitor of carrier-mediated uptake. The initial rates of D-galactose carrier-mediated transport, generated at low concentration (10 microM) were very temperature-sensitive and yielded a non-linear Arrhenius plot. An Arrhenius plot of Vmax, generated with higher concentrations, was linear. The linearity of the Vmax Arrhenius plot, in conjunction with the high cholesterol content of this membrane preparation, suggests that a membrane lipid phase transition is not responsible for the non-linearity of the low concentration Arrhenius plot. A discontinuous temperature sensitivity of the interaction between D-galactose and the hexose transport system, as reflected by a marked sensitivity in Km, appears responsible for the non-linearity in this Arrhenius plot.

Phenobarbital modulates the (Na+, K+)-stimulated ATPase and Ca2+-stimulated ATPase activities by increasing the bilayer fluidity of dog brain synaptosomal plasma membranes

The binding of [14C]phenobarbital into synaptosomal plasma membranes of dog brain follows a sigmoid path. The "best fit" curve of this binding is the one described by the Hill equation (r2 less than 0.93 and Hill coefficient, n = 1.32). (Na+, K+)-stimulated ATPase and Ca2+-stimulated ATPase activities are modulated by phenobarbital. Arrhenius plots of (Na+, K+, Mg2+)-dependent ATPase revealed that phenobarbital (2 mM) lowered the transition temperature and altered the Arrhenius activation energies of this enzyme. The allosteric inhibition by F- of the (Na+, K+)-stimulated ATPase was studied in control and phenobarbital-treated membranes. The lowering of the transition temperature and changes in Arrhenius activation energy about the transition temperature in combination with changes observed in the allosteric properties of the (Na+, K+)-stimulated ATPase by F-, produced by phenobarbital, would be expected if it is assumed that phenobarbital "fluidizes" synaptosomal plasma membranes.

Electron spin resonance studies of the effects of lipids on the environment of proteins in mitochondrial membranes

The physical state of mitochondrial membranes has been investigated by means of stearic acid spin labels and of a maleimide spin label covalently bound to protein sulfhydryl groups. Stearic acid spin labels 5-NS and 16-NS show that n-butanol enhances the lipid fluidity of mitochondrial membranes in the whole temperature range between 4 and 37 degrees C; the effects in the hydrophobic membrane core, probed by 16-NS, are already apparent at 10 mM butanol. In liposomes formed of mitochondrial phospholipids, a fluidizing effect appears only at much higher concentration. Such results are compatible with the idea that butanol destabilizes lipid-protein interactions. On the other hand, the ratio between weakly and strongly immobilized SH groups probed by maleimide spin label is only slightly affected in the temperature range of 4-37 degrees C by addition of high concentrations of n-butanol, indicating that the environments probed are stable to agents inducing fluidity changes in the lipids. There are, however, indications that the environment probed by maleimide is affected by lipids, since the spin label, when bound to lipid-depleted mitochondria, becomes more immobilized, reconstitution of such lipid-depleted membranes with phospholipids restores the original spectra.

Ethanol effects on striatal dopamine receptor-coupled adenylate cyclase and on striatal opiate receptors

The perturbation of neuronal cell membranes by ethanol may result in specific functional changes through modification of the activity of various membrane-bound proteins. In mouse striatum, adenylate cyclase, a membrane-bound enzyme, is coupled to dopamine, as well as to opiate, receptors. Ethanol stimulates striatal adenylate cyclase activity by modifying the regulatory protein ("G-protein")-adenylate cyclase interaction to produce an increased amount of activated enzyme. This action is additive with the effects of dopamine on adenylate cyclase. Ethanol also modifies striatal opiate receptor-effector coupling processes. In the presence of ethanol, opiate receptor affinity is altered, and this alteration is modified by GTP, suggesting that ethanol influences the interaction of the opiate receptor complex with the G-protein. Our results suggest that ethanol can affect receptor-effector coupling, including the binding of opiate agonists to their receptors, through its membrane-disordering capacity, and that particular systems may react in a relatively specific manner with ethanol.

Effects of ethanol on Arrhenius parameters and activity of mouse striatal adenylate cyclase

Arrhenius plots of basal and dopamine (DA)-stimulated adenylate cyclase activities exhibited discontinuities at 20 degrees, while the plot of fluoride-stimulated adenylate cyclase activity was linear over the studied temperature range. None of the Arrhenius parameters were altered by in vitro addition of ethanol (75 or 750 mM) to enzyme assay mixtures, and Arrhenius parameters were found to be unchanged when enzyme obtained from animals rendered tolerant to, and physically dependent on, ethanol was assayed. The differences between the response to ethanol of adenylate cyclase and the response of other membrane-bound enzymes [e.g. (Na+-K+)ATPase], as measured by Arrhenius plots, may indicate different sites of action of ethanol. When the specific activity of adenylate cyclase was examined, ethanol was found to stimulate activity at all temperatures tested. The dose-response curve for ethanol activation of basal adenylate cyclase activity was shifted to the right for enzyme obtained from mice chronically treated with ethanol. Analysis of the data indicated that activation of adenylate cyclase by ethanol (as well as by DA) was an entropy-driven process. Since ethanol treatment did not affect the Arrhenius parameters, which appear to be associated with membrane lipids, it is suggested that enzyme activation by ethanol results from direct effects on the enzyme or regulatory protein. Resistance to this effect occurs through changes in protein conformation following chronic ethanol treatment.

Evidence against a generalized membrane defect in dystrophic mice platelets

The response of the membrane-bound enzyme AChE to changes in temperatures was investigated to test the applicability of the "generalized membrane defect" hypothesis proposed for human myotonic and Duchenne muscular dystrophies to the two forms of muscular dystrophy expressed in mice. For intact platelets from homozygous normal and dystrophic mice of both strains, a break (Tc) occurred in the Arrhenius plot of AChE activity at approximately 22 C. Solubilization of membrane-bound AChE by Triton X-100 produced a nonlinear Arrhenius plot over the temperature range (7.7 C to 37 C) in normal and dystrophic mice of both strains. However, in the presence of phospholipase A2 + C and Triton X-100, a linear Arrhenius plot was produced indicating that the membrane-bound enzyme is normally modulated by a bulk lipid domain as well as by a tightly bound (immobilized) phospholipid domain. The temperature response of platelet AChE from normal and dystrophic mice of both strains was not significantly different. These results showing normal temperature kinetics of AChE do not lend support to the theory of a membrane defect in the platelets of dystrophic mice.

Effect of lithium on synaptosomal brain enzymes

During 7 days of lithium administration to rats, the levels of adenylate cyclase bound to brain synaptosomes decreased, while those of acetylcholinesterase increased. Both enzyme levels returned to their initial values after 1 month of treatment. Monoamine oxidase, which is bound to a mitochondrial membrane, was not affected by lithium treatment. Arrhenius plots of the brain synaptosomal enzymes (Na + K)ATPase and acetylcholinesterase from rats treated with LiCl for 7 or 30 days showed a lower transition temperature. Also, when these synaptosomal enzymes were exposed to such exogenous agents as detergents or alcohol, the reaction of the enzymes obtained from lithium treated rats was different than that of control rats. These effects disappeared after ceasing lithium administration for one week. These data indicate changes in the structure of brain membranes after lithium administration.

The rate of osmotic hemolysis: a relationship with membrane bilayer fluidity

A first-order semilogarithmic plot of the decrease in turbidity that takes place during hemolysis is used to define an apparent rate of hemolysis. The effect on this rate of hemolysis of various membrane modifications is studied. Triton X-100, ethanol and chlorpromazine, which dissolve into the membrane, all increase the rate of hemolysis, even though the same concentration of ethanol and chlorpromazine has been shown to decrease the osmotic fragility. Glutaraldehyde, azodicarboxylic acid-bisdimethylamide (diamide) and intracellular Ca2+ are used to produce cross-links on membrane proteins. All of these reagents decrease cell deformability but have different effects on the rate of hemolysis, with Ca2+ increasing, glutaraldehyde decreasing and diamide producing almost no effect on the rate. These modifications are also found to alter the ESR spectra of the stearic acid spin-label, 2-(14-carboxytetradecyl)-2-ethyl-4,4-dimethyl-3-oxazolidinyloxyl, which probes mobility in the hydrophobic core of the lipid bilayer. A correlation between the effect of membrane modifications on bilayer fluidity and the rate of hemolysis suggests that the rate-limiting process which determines the rate of hemolysis involves rupturing of the bilayer.

On the mechanism of action of anesthetics. Direct inhibition of mitochondrial F1-ATPase by n-butanol and tetracaine

The concentrations of n-butanol and tetracaine required for 50% inhibition of the ATPase activity of F1 particles isolated from bovine heart mitochondria were 160 mM and 1.1 mM, respectively. The results are offered as evidence that the physiological effects of these anesthetics may be due to direct interaction with membrane proteins rather than with the lipids.

The effect of temperature on the growth and lipid composition of the extremely halophilic coccus, Sarcina marina

Sarcina marina (NCMB 778) grew over the temperature range 20-45 degrees C but no growth was recorded at 15 degrees C or 50 degrees C. At the optimum growth temperature of 34 degrees C the doubling time was 14.5 h. The major polar lipid components, tentatively identified as the diether analogues of phosphatidyl glycerophosphate (PGP), phosphatidyl glycerol (PG), diglycosyl diglyceride (DGD) and triglycosyl diglyceride (TGD), and the major neutral lipid components, tentatively identified as squalene, dihydrosqualene, tetrahydrosqualene, vitamin MK8, geranyl geraniol and di-O-phytanyl glycerol, are identical to those found in other extremely halophilic rods and cocci. The total lipid content varied with growth conditions from 0.6-3.2% of the dry cell weight, polar lipids accounted for between 94.3 and 83.6% of the total lipid, the remainder being neutral lipid. In response to both the transition from exponential to stationary phase and a reduction of 14 degrees C in growth temperature, batch cultures showed: (i) an increase in total lipid content; (ii) a decrease in PG and (iii) an increase in PGP. Specific responses to the temperature decrease were (i) increased total lipid content; (ii) no decrease in neutral lipids in stationary phase; (iii) marked reduction in PG and (iv) raised DGD. (i) and (ii) could be mechanisms for increasing membrane fluidity. In common with all other extreme halophiles investigated the alkyl side chains of S. marina polar lipids were identified as the phytanyl (3R, 7R, 11R, 15-tetramethylhexadecyl) group. Its structure did not appear to vary with temperature so that the normal mechanisms for modifying the structure of lipid alkyl side chains to modulate membrane fluidity in response to temperature changes probably does not occur in this group of microorganisms.

Effects of temperature and pH on the water exchange through erythrocyte membranes: nuclear magnetic resonance studies

The temperature and pH dependence of water exchange has been studied on isolated erythrocytes suspended in isotonic buffered solutions. At pH 7.4 a break in the Arrhenius plot of water exchange time at around 26 degrees C was found. The mean value of the apparent activation energy of the water exchange time at temperatures higher than that of the discontinuity was 5.7 kcal/mole (+/- 0.4); at lower temperatures the values of the apparent activation energy were below 1.4 kcal/mole. The pH dependence of water exchange time of isolated erythrocytes revealed a marked increase of the water exchange time values in the acid range of pH; a much smaller variation of the same parameter occurs between pH 7.0 and 8.0. These finding could be correlated with other processes involving erythrocyte membranes that showed similar pH and temperature dependence and were considered to indicate state transitions in the membranes. It is suggested that the temperature and pH effects on water diffusion indicate that conformational changes and cooperative effects are implicated in the mechanism of this transport process.

Action of barbiturates on activity of acetylcholinesterase from synaptosomal membranes

The acetylcholinesterase from synaptosomal membranes is inhibited by anesthetics: Nembutal, brietal, and thiopental. Nembutal and brietal decrease the Km for acetylthiocholine, without changes in Vmas. A noncompetitive type of inhibition is produced by thiopental. This anesthetic decreases Arrhenius plot discontinuity by about 4 degrees C and increases activation energies. Nembutal and brietal do not change Arrhenius plot discontinuities, but they increase activation energies. These results suggest that barbiturates change lipid-protein interactions in synaptosomal membranes.

The effect of halothane on mice selectively bred for differential sensitivity to alcohol

We have investigated the response of mice to halothane that have been selectively bred for either sensitivity (long sleep, LS) or resistance (short sleep, SS) to the anesthetic effects of ethanol. While large differences in the response of the animals to ethanol were observed in sleep time, blood anesthetic concentration at time of awakening, and body temperature, the SS and LS lines did not differ in their response to halothane. We conclude that the mechanism of action of ethanol and halothane differ in a significant way from each other.

Initial membrane reaction in peptidoglycan synthesis: perturbation of lipid-phospho-N-acetylmuramyl-pentapeptide translocase interactions by n-butanol

Phospho-N-acetylmuramyl-pentapeptide translocase, the initial membrane enzyme in the biosynthesis of peptidoglycan, requires a lipid microenvironment for function. n-Butanol was reversibly intercalated into membranes to perturb the hydrophobic interactions in this microenvironment in order to define further the role of lipid. In the concentration range for maximal stimulation of enzymic activity (0.12-0.18 M), n-butanol causes a 40% decrease in the fluorescence emission of the dansylated product, undecaprenyl diphosphate-(N epsilon-dansyl)pentapeptide. Since no change in emission maximum occurs below 22 degrees C in the presence of 0.12 M n-butanol, it is concluded that intercalation of this alkanol causes an increase in fluidity. Above 22 degrees C this concentration of n-butanol causes both a decrease in the fluorescence emission and a red shift in the emission maximum. It is concluded that a polarity change as well as fluidity change occurs above 22 degrees C. n-Butanol also causes a significant change in the phase transition experienced by the dansylated lipid product. Thus, it is possible with n-alkanols, e.g. n-butanol, to perturb lipid-translocase interactions resulting in an increase in fluidity in the microenvironment of the enzyme. This change in fluidity correlates with a stimulation of enzymic activity.

Receptor and membrane function in the alcohol tolerant/dependent animal

Neurochemical changes which are associated with the development or expression of tolerance to or physical dependence on ethanol may be expected to display a time course of appearance and disappearance which correlates positively with the time course for tolerance or dependence. Previous studies of striatal dopaminergic receptor function indicated that ethanol-withdrawn mice displayed decreased physiological and biochemical responses to dopamine (DA) agonists, which could be best explained by postulating an inefficient coupling between DA receptors and various receptor-mediated processes, possibly as a result of ethanol-induced changes in neuronal membrane properties. The membrane-bound enzyme, (Na+-K+)ATPase, obtained from ethanol-withdrawn animals, displays an altered transition temperature and resistance to the effects of ethanol on enzyme activity. These changes also suggest compensatory alterations in neuronal membrane properties. All of these alterations show a time course of disappearance which corresponds to that for the disappearance of tolerance to the hypothermic and sedative effects of ethanol. Ethanol-withdrawn mice also display increased numbers of hippocampal muscarinic cholinergic receptors; however, the time course for the increase in receptor number appears to correlate with that of withdrawal symptomatology. Thus, compensatory changes in neuronal membrane properties in response to ethanol may be expressed via diverse functional changes.

Lipid protein interactions in mitochondria. VII. A comparison of the effects of lipid removal and lipid perturbation of the kinetic properties of mitochondrial ATPase

We investigated the kinetics of mitochondrial ATPase in bovine heart mitochondria and submitochondrial particles upon treatment with phospholipase A2, or upon addition of n-butanol to perturb the lipid protein interactions. The changes observed are the following: (1) Lipid removal or perturbation with butanol is accompanied by loss of ATPase activity with decrease of both V and of the KM for ATP. (2) There are changes of activation energy of ATPase activity at temperatures above the discontinuity normally observed for membrane-bound enzymes in mitochondria. In particular, butanol abolishes the discontinuity, and induces a constant activation energy of about 32 kcal/mol in the range 8--37 degrees C. (3) Butanol modifies the pH dependence of ATPase shifting the pH optimum from around 10 to less alkaline values. The optimum for Mg2+ concentrations is increased by the solvent. (4) Treatment with phospholipase A2 results in a removal of oligomycin-sensitive ATPase, whereas butanol addition prevents oligomycin inhibition of ATPase. (5) In beef heart mitochondria, a spin-labelled analog of the inhibitor, dicyclohexyl carbodiimide, did not show any change in environment upon butanol addition, unlike that found in mitochondria from Saccharomyces cerevisiae.

Initial membrane reaction in peptidoglycan synthesis. Interaction of lipid with phospho-N-acetylmuramyl-pentapeptide translocase

The initial membrane reaction in the biosynthesis of peptidoglycan is catalyzed by phospho-N-acetylmuramyl (MurN Ac)-pentapeptide translocase (UDP-MurNAc-Ala-gamma DGlu-Lys-DAla-DAla undecaprenyl phosphate phospho-MurNAc-pentapeptide transferase). In addition to the transfer reaction, the enzyme catalyzes the exchange of [3H]uridine monophosphate with the uridine monophosphate moiety of UDP-MurN Ac-pentapeptide. Two distinct discontinuities are observed in the slopes of the Arrhenius plots of the exchange and transfer activities at 22 and 30 degrees C for the enzyme from Staphylococcus aureus Copenhagen. Anisotropy measurements of perylene fluorescence and electron spin resonance measurements of N-oxyl-4',4'-dimethyloxazolidine derivatives of 12- and 16-ketostearic acid intercalated into membranes from this organism define the lower (T1 = 16--22 degrees C) and upper (Th = 30 degrees C) boundaries of a phase transition. These values correlate with the discontinuities observed for the activity measurements. Thus, it is proposed that the physical state of the lipid micro-environment of phospho-MurNAc-penetapeptide translocase has a significant effect on the catalytic activity of this enzyme.

Lipid protein interactions in mitochondria. VIII. Effect of general anesthetics on the mobility of spin labels in lipid vesicles and mitochondrial membranes

We have studied the effect of general anesthetics on the mobility of two stearic acid spin labels (5-doxyl stearic acid and 16-doxyl stearic acid) in bovine heart mitochondria and in phospholipid vesicles made from either mitochondrial lipids or commercial soybean phospholipids. The general anesthetics used include nonpolar compounds (alcohols, halothane, pentane, diethyl ether, chloroform) and the amphiphatic compound, ketamine. All anesthetics tested increase the mobility of the spin labels in phospholipid vesicles to a limited extent up to a concentration where the ESR spectra become those of free spin labels. On the other hand, anesthetics have a pronounced effect on mitochondrial membranes at concentrations as low as those known to produce general anesthesia; the effect is lower near the bilayer surface (5-doxyl stearic acid) and very strong in the bilayer core (16-doxyl stearic acid). The effects of anesthetics are mimicked by the detergent, Triton X-100. We suggest that the discrepancy between the action of anesthetics in mobilizing the spin labels in lipid vesicles and in membranes results from labilization of lipid protein interactions.

Differential scanning calorimetry and enzymic activity of rat liver microsomes in the presence and absence of delta1-tetrahydrocannabinol

The thermal transitions of rat liver microsomes and isolated lipids were investigated by using differential scanning calorimetry. Endothermic transitions at approximately-5 degrees C and between approximately18 degrees and 40 degrees C were detected in the membranes and at approximately-10 degrees C and between approximately 10 degress and 20 degrees C in the extracted lipids. Interaction with delta1-tetrahydrocannabinol of microsomal membranes and of extracted lipids influences the thermotrophic behaviour as revealed by differential scanning calorimetry and eliminates the break in the Arrhenius plot of the enzymic activity of O-demethylase.