Phospholipid Membrane Fluidity Research Articles

Interaction between soybean oleosome-associated proteins and phospholipid bilayer and its influence on environmental stability of luteolin-loaded liposomes

Soybean oleosome-associated protein (SOP) plays a vital role in stabilizing soy oleosomes owing to its unique amphipathic topological structure. Inspired by the structure of natural oleosomes, in the current study, SOP-decorated liposomes (SOP-Lips) were proposed as a vehicle for improving phospholipid bilayer membrane stability. The micro morphology, size, encapsulation efficiency, and retention rate of SOP-Lips were characterized, the interactions between SOP and the phospholipid bilayer and their effects on the protein and lipid bilayer structures were evaluated. When the liposomes/SOP mass ratio was 1: 0.2 and 1: 0.4, the SOP-Lips exhibited spherical morphology and favorable dispersibility. The quartz crystal microbalance with dissipation monitoring (QCM-D) result suggested that most of SOP bound to liposomes in a tightly integrated way. Spectroscopy analysis indicated that the aromatic amino acids in the protein were exposed to a more hydrophobic microenvironment due to the interactions between the SOP and liposomes. There was an increase in α-helix and decrease in β-sheet and random curl contents in SOP upon exposure to liposomes. The decoration of SOP to liposomes could decrease membrane fluidity and enhance lateral packing of the phospholipid fatty acyl chain. The SOP coating increased the pH, ionic strength and temperature stability of luteolin liposomes (LUT-Lips). In the simulated digestion, SOP-decorated luteolin liposomes (SOP-LUT-Lips) showed a delayed release effect compared with LUT-Lips, suggesting that the inclusion of SOP resulted in a more digestion-resistant structure. This work provides a viable strategy for using SOP-Lips as a delivery system for nutraceuticals in functional food, dietary supplements and pharmaceuticals. • Soybean oleosome-associated protein (SOP) decorated liposomes were constructed. • SOP interacted with liposomes through hydrogen bonding and hydrophobic interaction. • SOP decreased phospholipid membrane fluidity and enhanced the bilayer orderness. • Inclusion of SOP increased the load efficiency of luteolin in liposomes. • SOP modified liposomes exhibited sustained luteolin release profile.

Co-hybridized composite nanovesicles for enhanced transdermal eugenol and cinnamaldehyde delivery and their potential efficacy in ulcerative colitis

Percutaneous absorption of drugs can be enhanced by ethosomes, which are nanocarriers with excellent deformability and drug-loading properties. However, the ethanol within ethosomes increases phospholipid membrane fluidity and permeability, leading to drug leakage during storage. Here, we developed and characterized a new phospholipid nanovesicles that is co-hybridized with hyaluronic acid (HA), ethanol and the encapsulated volatile oil medicines (eugenol and cinnamaldehyde [EUG/CAH]) for transdermal administration. In comparison with EUG/CAH-loaded ethosomes (ES), the formulation stability and percutaneous drug absorption of EUG/CAH-loaded HA-immobilized ethosomes (HA-ES) were significantly improved. After transdermal administration of HA-ES, the interstitial cells of Cajal in the colon of rats with trinitrobenzene sulfonate-induced ulcerative colitis (UC) were significantly increased, and the stem cell factor/c-kit signaling pathway was partly repaired. Overall, HA-ES possesses excellent deformability and showed improved efficacy against UC compared with ES, which is demonstrated as a promising transdermal delivery vehicle for volatile oil medicines.

Phospholipid Membrane Fluidity Alters Ligand Binding Activity of a G Protein-Coupled Receptor by Shifting the Conformational Equilibrium.

The affinity of a ligand for a receptor on the cell surface will be influenced by the membrane composition. Herein, we evaluated the effects of differences in membrane fluidity, controlled by phospholipid composition, on the ligand binding activity of the G protein-coupled receptor human serotonin 2B. Using Nanodisc technology to control membrane properties, we performed biophysical analysis and employed molecular dynamics simulations to demonstrate that increased membrane fluidity shifted the equilibrium toward an active form of the receptor. Our quantitative study will enable development of more realistic in vitro drug discovery assays involving membrane-bound proteins such as G protein-coupled receptors.

Effect of esters based on terpenoids and GABA on fluidity of phospholipid membranes

The influence of esters based on gamma-aminobutyric acid (GABA) and mono-/bicyclic terpenoids on membrane structure was investigated. The mechanism of action for terpenoid esters on phospholipids of artificial membranes and lipids isolated from the rat stratum corneum was studied by fluorescence and FT-IR spectroscopy. We report here, that inclusion of monocyclic terpenoid esters in phospholipid liposomes leads to growth of excimer to monomer ratio (IE/IM) indicating a decrease of membrane microviscosity. Another mechanism of influence on biomembranes was proposed for ester of bicyclic borneol - in this case a high ratio of vibronic peak intensities (I1/I3) was revealed. The addition of terpenoid esters appears in the FT-IR spectra as intensity reduction of absorption bands associated with C = O, P = O and P–O–С groups of lecithin phospholipids. Similar results were obtained after esters addition to lipids isolated from stratum corneum indicating a decrease of hydrogen bonds number between polar groups of lipids. Thus, the influence of terpenoid esters on molecular organization of the lipid matrix substantiates the feasibility of their use after transdermal delivery in vivo.

PH-Induced Changes in the Surface Viscosity of Unsaturated Phospholipids Monitored Using Active Interfacial Microrheology.

Lipid membranes, a major component of cells, are subjected to significant changes in pH depending on their location in the cell: the outer leaflet of the cell membrane is exposed to a pH of 7.4 whereas lipid membranes that make up late endosomes and lysosomes are exposed to a pH of as low as 4.4. The purpose of this study is to evaluate how changes in the environmental pH within cells alter the fluidity of phospholipid membranes. Specifically, we studied pH-induced alterations in the surface arrangement of monounsaturated lipids with zwitterionic headgroups (phosphoethanolamine (PE) and phosphocholine (PC)) that are abundant in plasma membranes as well as anionic lipids (phosphatidylserine (PS) and phosphatidylglycerol (PG)) that are abundant in inner membranes using a combination of techniques including surface tension vs area measurements, interfacial microrheology, and fluorescence/atomic force microscopy. Using an active interfacial microrheology technique, we find that phospholipids with zwitterionic headgroups show a significant increase in their surface viscosity at acidic pH. This increase in surface viscosity is also found to depend on the size of the lipid headgroup, with a smaller headgroup showing a greater increase in viscosity. The observed pH-induced increase in viscosity is also accompanied by an increase in the cohesion pressure between zwitterionic molecules at acidic pH and a decrease in the average molecular area of the lipids, as measured by fitting the surface pressure isotherms to well-established equations of state. Because fluorescent images show no change in the phase of the lipids, we attribute this change in surface viscosity to the pH-induced reorientation of the P--N+ dipoles that form part of the polar lipid headgroup, resulting in increased lipid-lipid interactions. Anionic PG headgroups do not demonstrate this pH-induced change in viscosity, suggesting that the presence of a net negative charge on the headgroup causes electrostatic repulsion between the headgroups. Our results also show that active interfacial microrheology is a sensitive technique for detecting minute changes in the lipid headgroup orientation induced by changes in the local membrane environment, even in unsaturated phospholipids where the surface viscosity is close to the experimental detection limit.

Effect of oxide nanoparticles on the morphology and fluidity of phospholipid membranes and the role of hydrogen bonds

Engineered oxide nanoparticles (NPs) are widely applied in insulators, catalyzers, paints, cosmetic products, textiles and semiconductors. Their attachment on cell membrane may lead to cytotoxicity. The effects of Al2O3, Fe2O3, SiO2, TiO2 and ZnO NPs on membrane integrity and fluidity were studied using giant or small unilamellar vesicles in this study. Al2O3 and SiO2 NPs disrupted the oppositely charged membrane, indicating the important role of electrostatic attraction. However, Fe2O3, TiO2 and ZnO NPs did not cause serious membrane disruption as Al2O3 and SiO2 NPs. Membrane fluidity was evaluated by the generalized polarity (GP) values of Laurdan fluorescent emission. SiO2 NPs induce the membrane gelation of both positively and negatively charged membrane. Al2O3 and ZnO NPs induced the gelation of the oppositely charged membrane, but did not cause obvious membrane gelation to the like charged membrane. The phospholipid molecular structural changes after NP exposure were analyzed by Fourier transform infrared (FT-IR) spectroscopy. FT-IR spectra revealed the hydrogen bond formation between NPs and the carbonyl/phosphate groups of phospholipids. Al2O3 and SiO2 NPs showed strongest evidence of hydrogen bonding on their FT-IR spectra. It was consistent with the microscopic observation and fluorescent data that Al2O3 and SiO2 NPs caused more serious membrane disruption and gelation. This study on membrane damage provides further knowledge on the cytotoxicity of nanomaterials and the safety of NP application.

Quercetin and epigallocatechin-3-gallate effect on the anisotropy of model membranes with cholesterol

Cell membrane fluidity, which can be altered by oxidative stress, plays an important role in the cell physiology. Flavonoids are among the most studied food substances that prevent and/or reduce oxidative stress, but their action mechanisms are far from being understood. We performed a study on the effect of quercetin and epigallocatechin-3-gallate on 2-Dimyristoyl-sn-glycero-3-phosphocholine small unilamellar vesicles (SUVs) with different amounts of cholesterol, using Laurdan as a fluorescent probe, to put into evidence the perturbations of the phospholipid membrane fluidity and local lipid order in an attempt to decipher the action mechanism of the flavonoids at the cell membrane level. Results indicate that polyphenols modulate the transition from the gel phase to the liquid crystalline phase of SUVs in all studied membranes. SUVs with cholesterol have by themselves higher phase transition temperature and the presence of polyphenols stabilizes further the membrane. Quercetin has a dose-dependent effect on the fluidity and local order of the lipid membranes, whilst epigallocatechin-3-gallate action is not dose-dependent, the differences being attributable to the hydrophobic/hydrophilic character of the substances. The findings are discussed within the frame of earlier reports on the effect of polyphenols on artificial membranes.

Ultrasmall superparamagnetic iron oxide (USPIO)-based liposomes as magnetic resonance imaging probes

BackgroundMagnetic liposomes (MLs) are phospholipid vesicles that encapsulate magnetic and/or paramagnetic nanoparticles. They are applied as contrast agents for magnetic resonance imaging (MRI). MLs have an advantage over free magnetic nanocores, in that various functional groups can be attached to the surface of liposomes for ligand-specific targeting. We have synthesized PEG-coated sterically-stabilized magnetic liposomes (sMLs) containing ultrasmall superparamagnetic iron oxides (USPIOs) with the aim of generating stable liposomal carriers equipped with a high payload of USPIOs for enhanced MRI contrast.MethodsRegarding iron oxide nanoparticles, we have applied two different commercially available surface-coated USPIOs; sMLs synthesized and loaded with USPIOs were compared in terms of magnetization and colloidal stability. The average diameter size, morphology, phospholipid membrane fluidity, and the iron content of the sMLs were determined by dynamic light scattering (DLS), transmission electron microscopy (TEM), fluorescence polarization, and absorption spectroscopy, respectively. A colorimetric assay using potassium thiocyanate (KSCN) was performed to evaluate the encapsulation efficiency (EE%) to express the amount of iron enclosed into a liposome. Subsequently, MRI measurements were carried out in vitro in agarose gel phantoms to evaluate the signal enhancement on T1- and T2-weighted sequences of sMLs. To monitor the biodistribution and the clearance of the particles over time in vivo, sMLs were injected in wild type mice.ResultsDLS revealed a mean particle diameter of sMLs in the range between 100 and 200 nm, as confirmed by TEM. An effective iron oxide loading was achieved just for one type of USPIO, with an EE% between 74% and 92%, depending on the initial Fe concentration (being higher for lower amounts of Fe). MRI measurements demonstrated the applicability of these nanostructures as MRI probes.ConclusionOur results show that the development of sMLs is strictly dependent on the physicochemical characteristics of the nanocores. Once established, sMLs can be further modified to enable noninvasive targeted molecular imaging.

Assessment of fluidity of different invasomes by electron spin resonance and differential scanning calorimetry

The aim of this study was to investigate the influence of membrane-softening components (terpenes/terpene mixtures, ethanol) on fluidity of phospholipid membranes in invasomes, which contain besides phosphatidylcholine and water, also ethanol and terpenes. Also mTHPC was incorporated into invasomes in order to study its molecular interaction with phospholipids in vesicular membranes. Fluidity of bilayers was investigated by electron spin resonance (ESR) using spin labels 5- and 16-doxyl stearic acid and by differential scanning calorimetry (DSC). Addition of 1% of a single terpene/terpene mixture led to significant fluidity increase around the C16 atom of phospholipid acyl chains comprising the vesicles. However, it was not possible to differentiate between the influences of single terpenes or terpene mixtures. Incorporation of mTHPC into the bilayer of vesicles decreased fluidity near the C16 atom of acyl chains, indicating its localization in the inner hydrophobic zone of bilayers. These results are in agreement with DSC measurements, which showed that terpenes increased fluidity of bilayers, while mTHPC decreased fluidity. Thus, invasomes represent vesicles with very high membrane fluidity. However, no direct correlation between fluidity of invasomes and their penetration enhancing ability was found, indicating that besides fluidity also other phenomena might be responsible for improved skin delivery of mTHPC.

Crystallization and preliminary X-ray crystallographic studies of DesR, a thermosensing response regulator in a two-component signalling system fromStreptococcus pneumoniae

The response regulator DesR, which activates the transcription of the des gene by binding to a regulatory region, is essential for controlling the fluidity of membrane phospholipids. DesR from Streptococcus pneumoniae was overexpressed in Escherichia coli. The protein was purified and crystallized for structural analysis. Diffraction data were collected to 1.7 A resolution using synchrotron radiation and the crystals belonged to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 46.91, b = 71.38, c = 117.73 A. Assuming the presence of a dimer in the asymmetric unit, this corresponds to a V(M) of 2.21 A(3) Da(-1).

Torpor patterns of hibernating eastern chipmunks Tamias striatus vary in response to the size and fatty acid composition of food hoards

Summary Many endotherms employ torpor during periods of resource scarcity, but this state of substantially reduced body temperature and metabolism appears to impose significant physiological costs. Accordingly, individuals can be expected to vary the expression of torpor according to the size of their energy reserves. Although dietary polyunsaturated fatty acids (PUFAs) are important for maintaining the fluidity of membrane phospholipids and depot fats at low body temperatures, they are also prone to autoxidation, which can result in significant somatic damage. Dietary PUFA may thus influence the depth and duration of torpor during hibernation. We evaluated the hypothesis that both an increase in the size of the burrow food hoard and an elevation of its PUFA composition can cause chipmunks to reduce their use of torpor both by reducing the time spent torpid and by maintaining higher body temperature during torpor. We provided individual chipmunks with equicaloric natural‐PUFA and high‐PUFA supplements 10 days prior to autumn immergence. We measured seven parameters that characterize the depth and duration of torpor used by hibernating chipmunks using temperature‐sensitive data loggers mounted on neck collars. We compared torpor patterns for the natural‐PUFA, high‐PUFA and control groups at a study site in southern Quebec, Canada. We also compared control animals from Quebec with unsupplemented controls from a more southerly site in Pennsylvania, USA characterized by higher food availability and less severe winters. Chipmunks provided with natural‐PUFA supplements spent less than half as much time in torpor as control animals at the same study site, and when in torpor they exhibited skin temperatures almost twice as high as controls. Chipmunks provided with high‐PUFA supplements significantly reduced the depth and duration of torpor bouts compared with animals provided with natural‐PUFA supplements. The torpor patterns of unsupplemented chipmunks at the southern site approximated those of natural‐PUFA chipmunks at the main study site. Our results provide clear evidence that chipmunks adjust the depth and duration of torpor expression according to both the size and the composition of their energy reserves. Furthermore, both the extent and the nutritional form of environmental energy availability are important determinants of the cost and benefits of torpor expression by free‐ranging endotherms.

Bacillus subtilis DesR Functions as a Phosphorylation-activated Switch to Control Membrane Lipid Fluidity

The Des pathway of Bacillus subtilis regulates the synthesis of the cold-shock induced membrane-bound enzyme Delta5-fatty acid desaturase (Delta5-Des). A central component of the Des pathway is the response regulator, DesR, which is activated by a membrane-associated kinase, DesK, in response to a decrease in membrane lipid fluidity. Despite genetic and biochemical studies, specific details of the interaction between DesR and the DNA remain unknown. In this study we show that only the phosphorylated form of protein DesR is able to bind to a regulatory region immediately upstream of the promoter of the Delta5-Des gene (Pdes). Phosphorylation of the regulatory domain of dimeric DesR promotes, in a cooperative fashion, the hierarchical occupation of two adjacent, non-identical, DesR-P DNA binding sites, so that there is a shift in the equilibrium toward the tetrameric active form of the response regulator. Subsequently, this phosphorylation signal propagation leads to the activation of the des gene through recruitment of RNA polymerase to Pdes. This is the first dissected example of a transcription factor functioning as a phosphorylation-activated switch for a cold-shock gene, allowing the cell to optimize the fluidity of membrane phospholipids.

Changes in brain intracellular pH and membrane phospholipids on oxygen therapy in hypoxic patients with chronic obstructive pulmonary disease.

Chronic hypoxia due to chronic obstructive pulmonary disease (COPD) constitutes a stress to cerebral metabolic homeostasis. Previous studies using phosphorus-31 magnetic resonance spectroscopy (31P MRS) have suggested that the brains of such patients utilize anaerobic glycolysis, which in neonatal, animal, and in vitro studies is associated with a protective intracellular alkalosis. To identify such a compensatory intracellular alkalosis in hypoxic COPD patients, in vivo cerebral 31P MRS was performed in eight patients and eight controls. The mean intracellular pH (pHi) in patients with COPD was similar to that of age-matched controls, but decreased in the patients with COPD by a mean pHi of 0.02 (p = 0.04), following supplemental oxygen. There was no change in cerebral pHi in normal subjects following oxygen administration. The broadband component of the MR spectrum increased in all the patients with COPD (p = 0.01), suggesting altered phospholipid membrane fluidity in the brain associated with the change in pHi following oxygen administration. The change in the broadband resonance was strongly correlated with the change in pHi (r = -0.68, p = 0.014). This study suggests that patients with COPD exhibit a compensatory change in pHi and abnormalities in cerebral membrane phospholipid conformation in the face of chronic hypoxia.

31P-MR spectroscopy in children and adolescents with a familial risk of schizophrenia.

Based on a previous report [9] on alterations of membrane phosphorus metabolism in asymptomatic family members of schizophrenic patients, the aim of the present study was to extend and improve the evaluation and data processing of (31)P spectroscopic data obtained from a larger study population by including an analysis of the broad spectral component (BC) of membrane phospholipids (PL). Eighteen children and siblings of patients with schizophrenia and a gender- and age-matched control group of 18 healthy subjects without familial schizophrenia were investigated with phosphorus magnetic resonance spectroscopy ((31)P-MRS) by using image selected in vivo spectroscopy (ISIS) in the dorsolateral prefrontal regions (DLPFR) of the brain. Spectral analysis was performed by using both the full and truncated FID to estimate metabolic peak ratios of different (31)P metabolites and the intensity and linewidth of the broad component. A significantly higher PDE level (p<0.01) and increased linewidth of the PDE components were observed for the high-risk group compared with the control group (p=0.02). No significant differences were observed for PME as well as for other (31)P-metabolites. No differences were observed between the left and right hemispheres for different normalised (31)P-metabolic levels. Decreased intensities (p=0.03) and smaller linewidths (p=0.01) were obtained for the broad component in the high-risk group. Impairments of membrane metabolism that are typical for schizophrenic patients are partially observed in adolescent asymptomatic family members of schizophrenics, including increased levels of low molecular PDE compounds indicating increased membrane degradation processes, no changes for PME, and decreased intensities and linewidths of the BC indicating changes in the composition and fluidity of membrane phospholipids. Despite limitations to completely suppress fast-relaxing components by dismissing initial FID data points, the spectroscopic results indicate additional changes in the membrane metabolism of high-risk subjects beyond changes of synthesis and degradation.

Modulation of α5β1 integrin functions by the phospholipid and cholesterol contents of cell membranes

Several modifications of the α5β1 integrin, which alter its intracellular and extracellular interaction with fibronectin and other proteins, have been reported. However, the significance of the lateral mobility of integrin molecules in the plasma membrane, as a regulator of their distribution and function, is poorly understood. We examined this problem by increasing the cholesterol content of plasma membranes, and consequently modifying the fluidity of membrane phospholipids, in rat fibroblasts. Under these conditions, the clustering of α5β1 integrin molecules in focal adhesions, their adhesion to the cell-binding domain of fibronectin, and their association with the cytoskeletal protein talin were significantly enhanced as compared to control cells. However, the activation of MAP-kinase pathways by the association of fibronectin with α5β1 integrin, and its association with integrin-linked kinase (ilk), were suppressed. The treated cells also showed distinct changes in shape, and their actin stress fiber network was more dense and thick as compared to control cells. The changes in fluidity of phospholipids occurred differentially and fluidity of phosphatidyl-ethanolamine increased, while that of phosphatidyl-choline was reduced. Our results suggest that proteins in focal adhesions could be partitioned in specific lipid domains, which regulate specific aspects of α5β1 integrin functions. J. Cell. Biochem.77:517–528, 2000. © 2000 Wiley-Liss, Inc.

Modulation of ?5?1 integrin functions by the phospholipid and cholesterol contents of cell membranes

Several modifications of the alpha5beta1 integrin, which alter its intracellular and extracellular interaction with fibronectin and other proteins, have been reported. However, the significance of the lateral mobility of integrin molecules in the plasma membrane, as a regulator of their distribution and function, is poorly understood. We examined this problem by increasing the cholesterol content of plasma membranes, and consequently modifying the fluidity of membrane phospholipids, in rat fibroblasts. Under these conditions, the clustering of alpha5beta1 integrin molecules in focal adhesions, their adhesion to the cell-binding domain of fibronectin, and their association with the cytoskeletal protein talin were significantly enhanced as compared to control cells. However, the activation of MAP-kinase pathways by the association of fibronectin with alpha5beta1 integrin, and its association with integrin-linked kinase (ilk), were suppressed. The treated cells also showed distinct changes in shape, and their actin stress fiber network was more dense and thick as compared to control cells. The changes in fluidity of phospholipids occurred differentially and fluidity of phosphatidyl-ethanolamine increased, while that of phosphatidyl-choline was reduced. Our results suggest that proteins in focal adhesions could be partitioned in specific lipid domains, which regulate specific aspects of alpha5beta1 integrin functions.

Local thrombus formation in the site of intravenous injection of chlorpromazine: possible colloid-osmotic lysis of the local endothelial cells.

Since amphiphilic drugs are known to interact with biomembranes, we investigated local vessel damage and thrombosis which might be brought about by intravenous dosing using chlorpromazine (CPZ) as a representative compound. CPZ-induced hemolysis was suppressed by an increase in sucrose concentration in the medium, characterizing this hemolysis to be colloid-osmotic lysis, which includes the enhancement of membrane phospholipid fluidity and consequent small pore formation in the membranes. This was supported by the observation that hemolysis by filipin, not featuring the stage of small pore formation, was not affected by sucrose. [14C]Glucose-entrapping liposomes were degraded by CPZ, and this degradation was enhanced by an increase in the intravesicle glucose concentration. These results indicated that the compound could induce colloid-osmotic lysis in erythrocytes and artificial membrane vesicles. CPZ also injured cultured porcine aortic endothelial cells (PAEC), as evidenced by lactate dehydrogenase (LDH) leakage. This injury was also suppressed by increase in sucrose concentration in the medium, suggesting that colloid-osmotic lysis again occurred. When rats were intravenously injected with CPZ, local endothelial cell (EC) injury and associated thrombus formation were observed, suggesting that CPZ's action was also evident in vivo. To our knowledge, this is the first finding which suggests that an intravenously dosed amphiphilic drug can injure local ECs based on a colloid-osmotic lysis mechanism leading to thrombosis.

Attenuation of motor nerve terminal repetitive discharge by the 21-aminosteroid tirilazad: evidence of a neural calcium antagonist action

Pretreatment with the 21-aminosteroid antioxidant compound tirilazad mesylate has been previously shown to retard the axotomy-induced anterograde degeneration of soleus motor nerve terminals in the cat. In the present study, we examined tirilazad's effects (7.7, 13.0 or 30.0 mg/kg twice daily P.O. for 6 days) on the excitability of normal cat soleus motor nerve terminals. Low frequency (0.4 Hz) neuromuscular transmission was measured as well as the occurrence of muscle contractile potentiation in response to either a 400 Hz/10 s episode of tetanic conditioning stimulation of the soleus nerve or the administration of a 200 μg/kg i.v. dose of the neuromuscular facilitatory drug edrophonium. The mechanism of the post-tetanic potentiation (PTP) or edrophonium-induced facilitatory response involves the occurrence of a stimulus-dependent repetitive discharge of the soleus motor nerve terminals due to an exaggeration of the nerve terminal Ca 2+-mediated after-depolarization. Tirilazad pretreatment caused a dose-related suppression of PTP and the edrophonium response indicative of a suppression of motor nerve terminal repetitive discharge. These effects were not shared by 6 days of oral pretreatment of cats with a high dose combination of the antioxidants vitamin E (200 I.U./day) and selenium (50 μg/day). Thus, it is unlikely that the antioxidant properties of tirilazad are involved in the suppression of motor nerve terminal excitability. Rather, it is proposed that tirilazad suppresses delayed motor nerve terminal Ca 2+ conductances secondary to its ability to decrease membrane phospholipid fluidity, and that this action might in some circumstances contribute to its neuroprotective activity.

Effects of soman on cerebral astrocyte plasma membranes: a freeze-fracture study

Astrocytes are identifiable on freeze-fracture by regular geometric aggregates of uniform intramembranous particles (IMP), the ‘orthogonal arrays’ (OA). These OAs are considered to be potassium channels that maintain the ionic balance around neurons. After subcutaneous administration of a single near LD50-dose of soman in rats, neurotoxic epileptogenic irreversible cholinesterase inhibitor, replicas showed a significant decrease in OA density in the convulsed animals. This dissociation by soman confirms that OA are a particularly labile membranes specialization. Frequent clumping of IMP and numerous cleavage planes were observed; this could be the result of an interaction between the liposoluble poison and membrane phospholipid fluidity.

深海耐圧性細菌の圧力応答

Although the deep - sea environment with high pressure and low temperature is rigorous for microorganisms in costal water, many barotolerant and barophilic bacteria are found to be inhabiting there. It is very important for the barophilic or barotolerant bacteria to maintain the physiological functions of cell membrane, because many vital functions are involved in the membrane. The fluidity of membrane composed by phospholipids and proteins is essential for the physiological functions. As high hydrostatic pressure raises the melting point of lipids and causes the phase transition of lipid within 100 MPa, barotolerant bacteria under high hydrostatic pressure appear to regulate the fluidity of membrane phospholipids. Therefore, the characterization of membrane at high pressure is indispensable to clarify the biochemical adaptation of bacteria to the environment. This report dealt with effects of pressure and temperature on the lipid composition of barotolerant deep - sea bacteria. The bacteria maintained the membrane fluidity by increasing unique fatty acids under high hydrostatic pressure.