Anesthetics may restructure the hydrogen belts of membranes

Differences in the fatty acid composition of KB-cells and gingival keratinocytes is culture medium additive dependent

The influence of culture medium additives foetal bovine serum (FBS), serum effective substitutes (SES) and human autologous serum on the fatty acid profile of KB-cells and human gingival keratinocytes was examined. The KB-cells were cultivated in RPMI medium added with FBS or SES and the gingival keratinocytes in D-MEM added with FBS or human autologous serum. Two days before the cells were prepared for gas chromatography (GC), the media were changed to serum- and antibiotic-free media. Whole fatty acids of the cells were analysed using GC and the fatty acid profiles were compared. KB-cells as well as gingival keratinocytes changed their fatty acid composition, according to the medium additive used. Significant differences were observed. In the case of KB-cells cultivated with SES the fatty acid changes suggest an increase of the membrane fluidity. Corresponding and significant differences were observed with gingival keratinocytes cultivated in medium added with human autologous serum: the membrane fluidity of the gingival keratinocytes was increased. It is supposed that an increased membrane fluidity caused by a different fatty acid spectrum of the host cell may relate to mechanisms of bacterial adhesion. Consequently, in vitro studies on invasion and adhesion of bacteria or virus are dependent on the medium used. Further analyses are necessary of the functional effects caused by differences in the content of specific FAs, especially with regard to the application of cultivated cells in the field of tissue engineering.

Liposome fluidization and melting point depression by pressurized CO2 determined by fluorescence anisotropy

The influence of CO2 on the bilayer fluidity of liposomes, which are representative of model cellular membranes, was examined for the first time at the elevated pressures (up to 13.9 MPa) associated with CO2-based processing of liposomes and microbial sterilization. Fluidization and melting point depression of aqueous dipalmitoylphosphatidylcholine (DPPC) liposomes by pressurized CO2 (present as an excess phase) were studied by steady-state fluorescence anisotropy using the membrane probe 1,6-diphenyl-1,3,5-hexatriene (DPH). Isothermal experiments revealed reversible, pressure-dependent fluidization of DPPC bilayers at temperatures corresponding to near-gel (295 K) and fluid (333 K) phases at atmospheric pressure, where the gel-to-fluid phase transition (Tm) occurs at approximately 315 K. Isobaric measurements (PCO2 =1.8, 7.0, and 13.9 MPa) of DPH anisotropy demonstrate substantial melting point depression (DeltaTm = -4.8 to -18.5 K) and a large broadening of the gel-fluid phase transition region, which were interpreted using conventional theories of melting point depression. Liposome fluidity is influenced by CO2 accumulation in the hydrocarbon core and polar headgroup region, as well as the formation of carbonic acid and/or the presence of buffering species under elevated CO2 pressure.

Interactions between cholesterol and lipids in bilayer membranes. Role of lipid headgroup and hydrocarbon chain-backbone linkage

We have employed four lipids in the present study, of which two are cationic and two bear phosphatidylcholine (PC) headgroups. Unlike dipalmitoylphosphatidylcholine, the other lipids employed herein do not have any ester linkage between the hydrocarbon chains and the respective lipid backbones. Small unilamellar vesicles formed from each of the PC and cationic lipids with or without varying amounts of cholesterol have been examined using the steady-state fluorescence anisotropy method as a function of temperature. The anisotropy data clearly indicate that the order in the lipid bilayer packing is strongly affected upon inclusion of cholesterol. This effect is similar irrespective of the electrostatic character of the lipid employed. The influence of cholesterol inclusion on multi-lamellar lipid dispersions has also been examined by 1H-nuclear magnetic resonance spectroscopy above the phase transition temperatures. With all the lipids, the line widths of (CH2)n protons of hydrocarbon chains in the NMR spectra respond to the addition of cholesterol to membranes. The influence on the bilayer widths of various lipids upon inclusion of cholesterol was determined from X-ray diffraction studies of the cast films of the lipid-cholesterol coaggregates in water. The effect of cholesterol on the efflux rates of entrapped carboxyfluorescein (CF) from the phospholipid vesicles was determined. Upon incremental incorporation of cholesterol into the phospholipid vesicles, the CF leakage rates were progressively reduced. Independent experiments measuring transmembrane OH- ion permeation rates from cholesterol-doped cationic lipid vesicles using entrapped dye riboflavin also demonstrated that the addition of cholesterol into the cationic lipid vesicles reduced the leakage rates irrespective of lipid molecular structure. It was found that the cholesterol induced changes on the membrane properties such as lipid order, linewidth broadening, efflux rates, bilayer widths, etc., did not depend on the ability of the lipids to participate in the hydrogen bonding interactions with the 3beta-OH of cholesterol. These findings emphasize the importance of hydrophobic interaction between lipid and cholesterol and demonstrate that it is not necessary to explain the observed cholesterol induced effects on the basis of the presence of hydrogen bonding between the 3beta-OH of cholesterol and the lipid chain-backbone linkage region or headgroup region.

Liposome-induced release of cell membrane proteins from intact tissue epithelium

During extraction and purification, membrane proteins very often undergo denaturation and deactivation. To overcome this problem, the authors have tried to establish a better methodology to make the study at in vivo tissue level, not at the isolated cellular level, possible and easier. This is in vivo direct exposure of animal tissue to the liposome that contains an artificial boundary lipid (D14DPC, 1,2-dimyristamido-1,2,-deoxyphosphatidylcholine). Bullfrog and rat tongues were used. To confirm the reasonableness of this methodology, several different techniques were adopted; the nerve response study, gel electrophoretic analysis, quartz crystal microbalance (QCM) measurement and the affinity gelchromatography. When the tongue was exposed to the D14DPC-containing DMPC liposome, a significant amount of membrane protein was found in the recovered liposome (this was the production of proteoliposome). The nerve response in the neurophysiological measurement to several taste stimuli, such as L-alanine, L-leucine, sucrose and quinine hydrochloride significantly decreased when the tongue was exposed to the same liposome. These phenomena were common to both bullfrog and rat tongues. The nerve response to the stimulation with L-alanine was the most remarkably affected in the liposomal treatment. Therefore, the L-alanine-binding protein was focused upon to confirm the reasonableness of the QCM measurement and the affinity gelchromatography. The D14DPC-containing proteoliposome always showed significant binding to both the L-alanine affinity gel and the L-alanine-conjugated QCM. The results revealed that membrane proteins can be directly and effectively released, even from intact animal tissue epithelium, using the artificial boundary lipid-containing liposome.

Minimum structural requirement for an inhalational anesthetic binding site on a protein target

The present study makes use of direct photoaffinity labeling and fluorescence and circular dichroism spectroscopy to examine the interaction of the inhalational anesthetic halothane with the uncharged alpha-helical form of poly(L-lysine) over a range of chain lengths. Halothane bound specifically to long chain homopolymers (190 to 1060 residues), reaching a stable stoichiometry of 1 halothane to 160 lysine residues in polymers longer than 300 residues. Halothane bound only non-specifically to an alpha-helical 30 residue polymer and to all of the polymers in their charged, random coil form. The data suggest that halothane binding is a function of supersecondary structure whereby intramolecular helix-helix clusters form in the longer polymers, resulting in the creation of confined hydrophobic domains. Circular dichroism spectroscopy cannot demonstrate changes in poly(L-lysine) secondary structure at any chain length with up to 12 mM halothane, suggesting that extensive hydrogen bond disruption by the anesthetic does not occur.

Comparison of perturbation effect of propranolol, verapamil, chlorpromazine and carbisocaine on lecithin liposomes and brain total lipid liposomes. An EPR spectroscopy study

Effect of verapamil, propranolol, chlorpromazine and carbisocaine on dynamics and/or order of liposomes (perturbation effect), prepared from different molar ratios of lecithin (PC) and rat brain total lipids (TL) was studied by EPR spectroscopy using spin probes 16-doxyl stearic acid and 14-doxyl phosphatidylcholine. The PC liposomes had higher dynamics and/or lower order than the TL liposomes. The perturbation effect of the drugs depended largely on the lipid composition of the liposomes. The drugs at the drug/lipid molar ratios from 0.1 to 1 increased membrane dynamics and/or decreased membrane order. The drugs had the most pronounced perturbation effect in the liposomes prepared from brain total lipids. The effect of the drugs decreased with decreasing the TL/PC ratio in the liposomes and was lowest, almost diminished, in the PC liposomes. Increasing concentration of the drugs decreased the difference between the dynamics and/or order of the PC and TL liposomes and so eliminated the influence of lipid composition on these membrane parameters. The results emphasize the role of lipid composition in studies concerning drug-lipid interactions in model and biological membranes.

Interaction of the herbicide atrazine with model membranes. II: Effect of atrazine on fusion of phospholipid vesicles

The effect of atrazine on Ca2+ induced fusion of cardiolipin(CL) and phosphatidylserine (PS) vesicles is studied by Tb3+/dipicolinic acid fluorescence and turbidity measurements. The interaction of herbicide with CL and PS membranes is studied by DPH fluorescence polarization. At low concentrations the pesticide partially inhibits fusion, especially in CL vesicles. Higher concentrations of atrazine decrease inhibition of fusion in CL, while fusion is slightly increased in PS. The Ca2(+)-induced increase of turbidity is not affected by atrazine in both PS and CL aggregation experiments. DPH polarization measurements show a perturbation only of the membrane hydrophobic core of PS, in presence of Ca2+. It is hypothesized that this biphasic effect shown by low and high atrazine concentrations on Ca2(+)-induced fusion of vesicles is due to a different localization of the pesticide in the membrane.

Progesterone enhances inhibitory responses of cerebellar Purkinje cells mediated by the GABAA receptor subtype

Previous studies from this laboratory have indicated that the sex steroid progesterone (P) is able to augment inhibitory responses of cerebellar Purkinje cells to the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) in the urethane anesthetized adult female rat. Because both GABAA and GABAB receptors are localized in this CNS area, agonist/antagonists for these receptors were utilized in the present evaluation in order to delineate the specific receptor subtype involved in P-GABA interactions. Systemically administered P was found to augment GABA-mediated inhibition by an average of 80%. Concomitant application of the GABAA blocker, bicuculline, greatly reduced this modulatory effect of the steroid. In contrast, P administration had no effect on baclofen-induced inhibition. These data suggest that P effects on GABA physiology are mediated predominantly at the GABAA receptor.

Influence of beta-adrenoceptor blocking drugs on lipid-protein interaction in synaptosomal membranes. An ESR study

The influence of the beta-adrenoceptor blocking drugs atenolol, doberol, propranolol and exaprolol on synaptosomal membranes was studied using ESR spectroscopy of stearic acid spin labeled at the 16th position. The drugs changed the ESR spectra of the label in the membranes, where in addition to changes of a fluid lipid component they increased the proportion of a motionally-restricted component. No motionally-restricted component was found in the samples prepared from brain total lipid liposomes treated with the drugs. The drug propensities at 20 mmol/l concentration to increase the proportion of the motionally-restricted component in the following order, control less than doberol approximately atenolol less than or equal to propranolol less than exaprolol did not correlate with their potency to influence the dynamics of the bulk lipid membrane phase. The motionally-restricted component induced by exaprolol increased with raising temperature and prolongation of time of the sample incubation. The results indicate that the beta-adrenoceptor blocking drugs influence lipid-protein interaction in the synaptosomal membranes, which could be important for elucidation of their mechanism of biological membrane activities.

Permeability of water and polar solutes in lipid bilayers

The three commonly used formalisms to describe water and solute permeation in lipid bilayers (namely, solubility-solute properties, activated rate processes and the thermodynamics of the irreversible process theory) are analyzed in the light of experimental results. These approaches are based on the consideration of the lipid bilayer as a composite membrane containing a hydrocarbon core, an H-bonded interfacial network and a fluctuating structure in which pores can appear. The particular structure of the lipid bilayer (i.e., a hydrophobic-hydrophilic leaflet) makes the permeation process of polar solutions more complicated than that occurring in inert polymeric membranes. Thus, the permeation theories of Fick, Henry and Kedem and Katchalsky should be adapted to introduce interfacial and elastic phenomena. A critical analysis of the experimental results available in the current literature opens the possibility to formulate a broader formalism for permeation in lipid membranes.

Spin label study of the perturbation effect of the local anaesthetics tetracaine and dibucaine on synaptosomes at pharmacological concentrations

The method of electron spin resonance spectroscopy of spin probes was used to determine the lowest concentrations of the local anaesthetics dibucaine and tetracaine exerting perturbations on synaptosome membranes. The perturbation depends on the temperature and the membrane depth, as well as on the concentration and the structure of the anaesthetics. Using spin labelled stearic acid at the 5th carbon position a negligible effect of the anaesthetics on the order parameter was found in the membrane both at 1 degree and 22 degrees, within the buffer concentration 0.01-10 mmol/l, but at 37 degrees and concentrations higher than 0.1 mmol/l the disordering effect was significant and of comparable efficiency for dibucaine and tetracaine. Employing stearic acid labelled at the 16th carbon position, disordering of the hydrocarbon core of the membrane caused by tetracaine or dibucaine was detected at 1 degree and 22 degrees, as well as at 37 degrees. The disordering effect occurred at buffer concentrations higher than 0.01 mmol/l for dibucaine, and higher than 0.1 mmol/l for tetracaine. At equal anaesthetic membrane concentrations and at the 16th carbon membrane depth, dibucaine was approximately twice as effective as tetracaine in perturbing synaptosomes. Tetracaine induced nonlamellar phases in the rat brain lipid membrane as detected by 31P NMR spectroscopy. The dynamic and structural perturbation effects of the local anaesthetics was found in that concentration range at which the anaesthetics influence various activities of biological membranes.

Locally applied progesterone metabolites alter neuronal responsiveness in the cerebellum

Ongoing studies in this laboratory have demonstrated that both systemically and locally administered sex steroids 17 beta estradiol (E2) and progesterone (P) alter cerebellar Purkinje cell responses to microiontophoretically applied amino acid neurotransmitters GABA and glutamate (GLUT) in the urethane-anesthetized, ovariectomized adult rat. In the present study, we have examined the effects of several locally pressure ejected P metabolites on Purkinje cell responsiveness to GABA and GLUT: 5 alpha-pregnane-20-one (5 alpha DHP), 5 alpha-pregnane-3 alpha-ol-20-one (3 alpha OH-DHP) and 5 alpha-pregnane-3 beta-ol-20-one (3 beta OH-DHP). GABA-induced inhibition was markedly enhanced immediately after onset of local application of 3 alpha OH-DHP or 5 alpha DHP, unaccompanied by alterations in background discharge. Both metabolites also attenuated excitatory responses to GLUT by 0-3 min after initiation of steroid application. In both cases, recovery to control levels of response was observed 6-9 min after termination of pressure application. These results are similar to those seen after local or systemic injection of P. In contrast, 3 beta OH-DHP did not produce any alteration in Purkinje cell responses to either amino acid. As 5 alpha DHP and 3 alpha OH-DHP can be localized in cerebellar tissue after P administration, the results presented here suggest that the neuronal effects of systemic P may be mediated by local membrane actions of P or its metabolites.

Phenobarbital competes with diacylglycerol for protein kinase C

Phenobarbital inhibits protein kinase C of rat brain by competitively displacing the effector of the enzyme, diacylglycerol. The drug appears to occupy the triple hydrogen bonding site which bonds diacylglycerol - and also phorbol esters - to the enzyme. It remains to be seen if the effect is responsible for the pharmaceutical activity of the drug; even so, it provides an example of a restructuring of lipid-protein hydrogen bonding, in the hydrogen belt of the membrane, in a manner postulated as a mechanism of anesthesia.

Mechanism of anesthesia: the potency of four derivatives of octane corresponds to their hydrogen bonding capacity

The anesthetic potency of four derivatives of n-octane was measured by tadpole righting reflex and expressed as effective millimolar concentration of drug in membrane, EDM50. Potency diminished (ED50 increased) in this order: 1-octanol, EDM50 = 5.5; 1-(2-methoxyethoxy)octane, EDM50 = 28; 1-methoxyoctane, EDM50 = 61; and 1-chlorooctane, EDM50 greater than 100. Since the aliphatic chain length was kept constant it is concluded that the differences in anesthetic potency are a consequence of the differences in head group structure. This result is predicted by a theory (Lipids 17, 1001-1003 [1982]) which holds that anesthesia is the result of a drug-induced restructuring of the hydrogen belts, those strata of the membrane that contain the hydrogen bond receiving and donating CO and OH groups of the membrane lipids and the adjoining proteins. The Meyer-Overton rule for anesthetics should be modified: chemicals induce anesthesia at equimolar in-membrane concentration provided their hydrogen-bonding parts are identical.

Membrane protein-lipid hydrogen bonding: evidence from protein kinase C, diglyceride, and tumor promotors

Membrane-bound proteins owe their retention and conformation in the lipid bilayer to hydrophobic peptide domains. Additional fixation, by protein-lipid hydrogen bonding, has been suggested, and recent reports on protein kinase C activation by diacylglycerol (DG) provide an unambiguous model for such bonding. The sn-1,2-diacylglycerol appears to donate a hydrogen bond from the sn-3 hydroxyl to the enzyme and to receive two hydrogen bonds, in the sn-1 and sn-2 ester CO groups, from the enzyme. This arrangement is confirmed in phorbol ester, a competitive inhibitor of DG for the kinase. This tumor promotor has a nearly identical spatial arrangement of hydrogen bond donor (9 alpha-OH) and acceptors (12 and 13 ester CO); so have two other tumor promotors, teleocidin and aplysiatoxin. There are reasons to believe that protein kinase C is not the only protein that is bound to membrane lipids by hydrogen bonding, and such bonding will have to be considered in membrane-associated events such as fusion, cross-membrane transport, or anesthesia.

Interfacial properties of model membranes and plasma lipoproteins containing ether lipids

The interfacial properties of synthetic ester and ether phosphatidylcholines (PCs) were investigated by using the polarity-sensitive fluorescent probes 6-propionyl-2-(dimethylamino)naphthalene (Prodan) and pyrene. The physical state of the phospholipid matrix was determined by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH). Single-bilayer phospholipid vesicles formed by sonication and model high-density lipoproteins were studied. On the basis of a number of spectroscopic and thermodynamic criteria, the interfacial regions of PCs and their ether analogues are similar. The fluorescence properties of Prodan in model lipoproteins or single-bilayer vesicles were independent of the phospholipid fatty acyl chain length and polar head group, as well as the substitution of ether linkage for ester bonds in the phospholipid. The spectral shifts correlated mainly with the physical state of the phospholipid. The emission spectrum of Prodan appeared at shorter wavelengths upon transfer from water to liquid-crystalline phospholipid and blue shifted further when the lipid was cooled to its gel phase. The effect of cholesterol in model high-density lipoproteins on the emission spectrum of Prodan was dose dependent and, at 18 mol % cholesterol, the spectrum was similar to that observed in a pure gel-phase lipid and was independent of temperature. The quantum yield of Prodan fluorescence in an ether-PC matrix was similar to that observed in water, whereas in an ester-PC matrix it was enhanced by a factor of about 5. Phospholipid-water partition coefficients of Prodan were independent of the physical state of 1,2-dimyristoyl-sn-glycero-3-phosphocholine or 1,2-tetradecyl-sn-glycero-3-phosphocholine.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of ganglioside insertion into brain membranes on the rate of ganglioside degradation by membrane-bound sialidase

Microsomal membranes isolated from calf brain contain a sialidase which cleaves ganglioside substrates naturally occurring within these membranes as well as exogenously added [3H]ganglioside GD1a. Micelles of [3H]ganglioside GD1a bind to the microsomal membranes in two steps. The first step, called adsorption, is fast and reversible by treatment with trypsin; the second step, called uptake, is slower and not reversible. The product of the enzymic degradation, [3H]ganglioside GM1, is exclusively located in the ganglioside pool taken up by the sialidase-bearing membranes, and not in the trypsin-releasable pool. Electron spin resonance (ESR) studies using a spin-labelled analogue of ganglioside GD1a indicate that the ganglioside uptake by microsomal membranes is accompanied by the disappearance of the micellar structure and by the 'dilution' of the probe molecules with membrane lipids. These findings suggest that exogenously added ganglioside substrate inserts into the microsomal membrane before it is recognized as substrate by the membrane-bound sialidase. Therefore, the influence of pH, ionic strength and membrane-fluidizing agents on the degradation rate measured with exogenous ganglioside GD1a does not only reflect kinetic parameters of the enzymic reaction itself but also the velocity of ganglioside insertion. Increasing ionic strength reduces the degradation rate. The acceleration of insertion with falling pH values shifts the measured pH optimum of the ganglioside degradation to lower values (pH 3.6) and masks the substantial residual sialidase activity at pH 5-7. The membrane-fluidizing alcohol n-hexanol greatly accelerates ganglioside insertion as well as ganglioside degradation. The latter was clearly demonstrated by studying the hydrolysis of endogenous ganglioside substrates, and is due to a decrease of the apparent Km value and an increase in the Vmax value. The Vmax value was also enhanced by freezing and thawing of the microsomal membranes.

The modulation of ion channels by the inhalation general anaesthetics. A1H-NMR investigation using unilamellar phospholipid membranes

The modulation of a variety of mechanisms of channel-mediated transport across unilamellar phospholipid membranes by a range of halogenated inhalation general anaesthetics (chloroform, enflurane, halothane and methoxyflurane) was investigated using 1H-NMR spectroscopy. Transport of the probe ion Pr3+ across egg yolk phosphatidylcholine (PC) and dipalmitoyl phosphatidylcholine (DPPC) vesicular membranes in the presence of the channel forming polypeptides alamethicin 30 and melittin, and the polyene antibiotic nystatin, as well as the degree of vesicular lysis at the gel to liquid-crystal phase transition of DPPC vesicles was monitored. The observation that the inhalation general anaesthetics inhibit such membrane permeability independently of the channel system or type of lipid used, suggests that hydrogen-bonded water structure and/or hydrogen-bonding centres at dipolar lipid-polypeptide interfaces, can be likely sites of action of the general anaesthetics.

Molecular interactions in the hydrogen belts of membranes. Glucose-6-phosphatase, lysophosphatidylcholine, and cholesterol

Microsomal glucose-6-phosphatase from rat liver is activated by phosphatidylcholine but inhibited by lysophosphatidylcholine. Inhibition occurs not by membrane lysis but in an intact bilayer; it is reversible; and it is overcome by addition of cholesterol but not if the cholesterol-hydroxyl group is blocked. An analog of lysophosphatidylcholine deprived of hydrogen bonding sites, 1-ether-2- deoxylysophosphatidylcholine , is a partial activator, and its effect on the enzyme in a phosphatidylcholine bilayer is not modulated by cholesterol. It appears to be one of the functions of cholesterol to buffer the lysophospholipids in membranes by complexing with them through hydrogen bonding in the hydrogen belt region. Lysophosphatidylcholine/cholesterol association is favored over phosphatidylcholine/cholesterol association.