The physical state of quick-frozen membranes and lipids

Lipid bilayers and biomembranes produce nearly identical calorimeter scans regardless of whether they are slowly cooled under near-equilibrium conditions or rapidly frozen at rates used in freeze-fracture electron microscopy. Except for the melting of ice at 273 K, for both cooling regimens no significant thermal events occur from 100 K to the usual gel to liquid crystal transition. The gel to liquid crystal transition itself is somewhat altered by rapid cooling when bilayers contain mixed lipid species. Combined with X-ray diffraction studies, the results indicate that quickly frozen bilayers are crystalline, but that the crystalline domains are quite small or otherwise disordered. In contrast to the behavior of lipids in bilayers, hexagonal-phase calcium cardiolipid easily forms a glass upon cooling.     

Effect of meleate on membrane physical state of brush border and basolateral membranes of the dog kidney

The effects of maleate on the physical state of isolated brush border and basolateral membranes from dog kidney cortex have been studied by fluorescence polarization and ESR methods. Anisotropy of 1, 6-diphenyl- 1,3,5-hexatriene and hyperfine splitting (2T₆) of 5-doxylstearic acid in brush border and basolateral membranes were not significantly modified by the addition of 10^?2 M maleate after 60–90 min treatment. These findings further support the view that maleic acid nephropathy is not due to a direct effect of maleate on tubular membranes per se.     

Receptor-independent interaction of bacterial lipopolysaccharide with lipid and lymphocyte membranes; the role of cholesterol

Lipopolysaccharide (LPS) is a major constituent of bacterial outer membranes where it makes up the bulk of the outer leaflet and plays a key role as determinant of bacterial interactions with the host. Membrane-free LPS is known to activate T-lymphocytes through interactions with Toll-like receptor 4 via multiprotein complexes. In the present study, we investigate the role of cholesterol and membrane heterogeneities as facilitators of receptor-independent LPS binding and insertion, which underpin bacterial interactions with the host in symbiosis, pathogenesis and cell invasion. We use fluorescence spectroscopy to investigate the interactions of membrane-free LPS from intestinal gram-negative organisms with cholesterol-containing model membranes and with T-lymphocytes. LPS preparations from Klebsiella pneumoniae and Salmonella enterica were found to bind preferentially to mixed lipid membranes by comparison to pure PC bilayers. The same was observed for LPS from the symbiote Escherichia coli but with an order of magnitude higher dissociation constant. Insertion of LPS into model membranes confirmed the preference for sphimgomyelin/cholesterol-containing systems. LPS insertion into Jurkat T-lymphocyte membranes reveals that they have a significantly greater LPS-binding capacity by comparison to methyl-β-cyclodextrin cholesterol-depleted lymphocyte membranes, albeit at slightly lower binding rates.     

Effect of cholesterol on the lateral nanoscale dynamics of fluid membranes

Inelastic neutron scattering was used to study the effect of 5 and 40?mol% cholesterol on the lateral nanoscale dynamics of phospholipid membranes. By measuring the excitation spectrum at several lateral q _|| values (up to q _||?=?3 ?^?1), complete dispersion curves were determined of gel, fluid and liquid-ordered phase bilayers. The inclusion of cholesterol had a distinct effect on the collective dynamics of the bilayer’s hydrocarbon chains; specifically, we observed a pronounced stiffening of the membranes on the nanometer length scale in both gel and fluid bilayers, even though they were experiencing a higher degree of molecular disorder. Also, for the first time we determined the nanoscale dynamics in the high-cholesterol liquid-ordered phase of bilayers containing cholesterol. Namely, this phase appears to be “softer” than fluid bilayers, but better ordered than bilayers in the gel phase.     

Effect of staphylococcal toxin on lymphocyte receptors and function

Staphylococcal toxin at a concentration of 10(-3) inhibits in vitro the rosette-formation of lymphocytes, taken from healthy donors and patients with purulent septic diseases, with sheep and mouse red blood cells, changes the ratio of lymphocyte subpopulation, modifies the spontaneous antigen- and mitogen-dependent migration of leukocytes. The latter phenomenon is not linked with disturbances in the lymphokine-producing activity of lymphocytes, but results from changes in the migration properties of granulocytes.     

小脑间位核对淋巴细胞功能的调节作用

目的:研究小脑深部核团之一间位核对淋巴细胞功能的调节作用,以拓宽对小脑功能的认识进而增加神经免疫学的知识.方法:在大鼠双侧小脑间位核内注射海人酸(KA)以损毁间位核内神经元的胞体,并设对照组,于小脑间位核内注入等量生理盐水.在手术后的第8、16、32 d分别用血细胞计数法检测动物外周血中淋巴细胞的数量;用四甲基偶氮唑(MTT)比色法检测动物肠系膜淋巴结细胞对刀豆蛋白A(Con A)刺激的增殖反应;用ELISA法检测动物血清中抗绵羊红细胞(SRBC)特异性IgM抗体的生成能力;用流式细胞术测定脾脏自然杀伤(NK)细胞的活性.结果:小脑间位核损毁后的第8、16、32 d,动物外周血中淋巴细胞数都明显低于损毁手术前的淋巴细胞数,也显著低于生理盐水对照组相应时间段的淋巴细胞数.在小脑间位核注射KA后的第8、16、32 d,动物的肠系膜淋巴结细胞由Con A诱导的增殖反应、血清中特异性抗SRBC IgM抗体的生成能力和脾脏NK细胞杀伤靶细胞YAC-1的活性均明显低于生理盐水对照组,但比较损毁后不同时间段的T、B和NK细胞功能的变化,没有发现显著的差异.结论:小脑双侧间位核损毁可导致总淋巴细胞数以及T、B和NK细胞功能均发生不可逆的降低,充分说明小脑间位核可调节淋巴细胞的功能,并提示在正常体内,小脑间位核对淋巴细胞功能具有增强效应.     

Effect of cholesterol on the stability of human erythrocyte membranes to electric breakdown

Electrical stability of human erythrocyte membranes with different cholesterol content was studied. Breakdown in the cell membranes was generated by application of electric pulses with field strengths of 1.4-3.2 kV/cm. The share of perforated cells was registered by measuring hemolysis level. The red blood cells from patients with psoriasis and normal erythrocytes after incubation in the presence of liposomes were used as a model of cells with cholesterol-rich membranes. It was discovered that an increase of cholesterol content in the membranes moved the field-dependent curves to a higher field range. The obtained effect is attributed to the increase of the breakdown membrane potential. Application of high-pulse-electric-field technique for investigating the properties of cell membranes is discussed.     

Influence of the bovine seminal plasma protein PDC-109 on the physical state of membranes.

PDC-109 is the main component of bovine seminal plasma and has been suggested to play an important role in the genesis of bovine sperm cells. Here, the effect of binding of PDC-109 to membranes on the structure and physical properties of the lipid phase was investigated. For that, ESR measurements were undertaken on model membranes (lipid vesicles) and on biological membranes (epididymal spermatozoa) by employing various spin-labeled phospholipids. We found that PDC-109 alters the membrane structure of lipid vesicles as well as of bovine epididymal spermatozoa in that the mobility of spin-labeled phospholipids was reduced in the presence of the protein. This immobilizing effect of the protein was not restricted to analogues of phosphatidylcholine but was also detected with spin-labeled phosphatidylethanolamine. However, the extent of immobilization was lower for phosphatidylethanolamine compared with phosphatidylcholine, supporting the lipid headgroup specificity of the protein. Besides phospholipid headgroups, the physical state of membrane lipids is also important for the interaction of PDC-109 with membranes, in that, e.g., the immobilizing effect of the protein on labeled lipids was larger in membranes above the phase transition temperature compared with the effect below this temperature. The results are of relevance for understanding the physiological role of PDC-109 in the genesis of sperm cells.     

Effect of chinoform on the function of biological membranes.

To investigate the mechanism by which the toxic effect of chinoform (5-chloro-7-iodo-8-quinolinol) develops, its action on the function of biological membranes was examined. Findings were: 1. Chinoform induced K+ release from red cells. This effect was increased by prior addition of Mg2+ and decreased by albumin, ruthenium red, or lanthanum chloride. 2. Chinoform induced K+ release from isolated rat liver mitochondria more effectively in the presence of Mg2+ or other bivalent cations, and a chinoform-Mg chelate was more effective than chinoform alone. The K+ release from mitochondria was protected by albumin and to a certain extent by lanthanum chloride. 3. The change in the ion permeability of mitochondrial membrane induced by chinoform in the presence of Mg2+ was accompanied by uncoupling of the oxidative phosphorylation. These results suggest that chinoform interacts with membranes more effectively as a metal chelate, producing conformational and functional changes in those membranes.     

Effect of ochratoxin A and ochratoxin C on the monocyte and lymphocyte function

The effect of practically relevant mycotoxin concentrations on functions of immune cells was studied in in vitro experiments. Porcine mononuclear cells were exposed to a crudeAspergillus-ochraceus toxin containing OTA, a HPLC fraction identical with OTC derived from the crude toxin (RE2), as well as pure OTA and OTC in a concentration range from 0.46 to 3000 ng/ml. The influence of mycotoxin exposure on metabolic activity, mitogen induced proliferation, expression of the activation marker CD25 and the cell cycle of lymphocytes and on the formation of free oxygen radicals as well as the production of the cytokines IL-6 and TNF-α by monocytes was determined. Exposure to high concentrations of all mycotoxin preparations lead to non-specific suppression of the immune cell functions, which was related to cytotoxic effects. Low concentrations caused ambivalent reactions, especially on monocyte function. In general, the HPLC fraction RE2 had an up to 100-fold stronger effect than pure OTA. Ochratoxin-induced suppression of lymphocyte proliferation was not abrogated by phenylalanine or aspartame. The results indicate that immunomodulation can be caused by very low mycotoxin concentrations which are not related to clinical symptoms or loss of performance.     

小脑顶核损毁对淋巴细胞功能的影响

目的：研究小脑顶核对淋巴细胞功能的调节作用,并初步探讨介导这种调节的中枢途径。方法：用海人酸（KA）毁损大鼠双侧小脑顶核,于术后第8d,取动物肠系膜淋巴结细胞和脾脏自然杀伤（NK）细胞进行体外培养,分别用四甲基偶氮唑（MTT）比色法检测由刀豆蛋白A（Con A）诱导的淋巴细胞的增殖反应,用流式细胞术测定NK细胞杀伤YAC-1肿瘤细胞的活性。同时用高效液相色谱法检测下丘脑中兴奋性神经递质谷氨酸的含量。结果：小脑双侧顶核注入KA后的第8d,小脑切片经Nissl染色,可见顶核内神经元胞体被有效破坏。此时,淋巴细胞对Con A诱导的增殖反应较双侧顶核注入生理盐水的对照组明显增强;而且NK细胞对YAC-1靶细胞的杀伤活性也明显高于对照组;同时下丘脑中谷氨酸含量较对照组明显减少。结论：小脑双侧顶核毁损可导致T和NK淋巴细胞功能明显增强,且下丘脑中谷氨酸含量显著下降,提示小脑顶核对淋巴细胞功能具有调节作用,小脑-下丘脑的谷氨酸能神经投射可能介导小脑顶核的免疫调节作用。     

Effect of ionic crosslinking on the water state in hydrogel chitosan membranes

The polyion complex membrane (PEC) composed of chitosan (Ch) and sodium alginate (NaAlg) designated for the separation of water/organic mixtures by pervaporation and/or direct methanol fuel cell technology was synthesized and analysed by FTIR, DSC, DTG and X-ray diffraction. The polyion complex formation between Ch (cationic polyelectrolyte) and NaAlg (anionic polyelectrolyte) was confirmed by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). The state of water in pure polyelectrolytes (PE) and PEC was studied by DSC. Results show that freezable and non-freezable water exist in analysed Ch, NaAlg and Ch/NaAlg hydrogels, while there are variations in the amount of non-freezing bound water in PE/water and PEC/water systems. Both ionic crosslinking as well as physical structure influence the state of water, and especially the non-freezable water content, in ionic hydrogel membranes.     

Effect of cholesterol administration on the state of the adrenal cortex in severe stress

The two weeks' effect of cholesterol on the rat adrenal cortex response under conditions of a severe stress was studied. In comparison with control, the degree of the gland activation and its alteration was found to decrease. It is suggested that the effect of cholesterol depends upon the action on the hypothalamus, and upon the adrenocortical tissue as well. The action of cholesterol on the adrenocortical tissue is bound with the cholesterol capacity to retard peroxydation reactions.     

Effect of calmodulin on the structural state of photoreceptor membranes and rhodopsin-containing phospholipid vesicles

The effect of calmodulin on the order of lipids in rhodopsin-free and rhodopsin-containing membranes has been studied using spin-label electron spin resonance methods. Calmodulin, up to 10(-6)M, did not change the measured order of lipids in bilayer membranes containing only rhodopsin. However, for bovine rod outer segment disc membranes, which contain rhodopsin and other proteins, calmodulin induced a significant concentration and temperature dependent increase in the order of the membrane lipids. This suggests that the site of calmodulin binding is remote from rhodopsin itself, and the nature of the binding appears to be a membrane surface phenomenon.     

Effect of infrequent feeding and increased physical activity on cholesterol kinetics in the rat.

The authors studied the effect of chronic physical exercise (running in a rotating drum at 850 m/hour, 5 times a week for 16 weeks) on the size of the cholesterol body pools and on cholesterol kinetics in adult male Wistar rats fed on a standard diet either ad libitum or 2 hours daily [33 weeks]. These data were obtained by mathematical analysis of the curve expressing the correlation of specific plasma cholesterol activity to time after a single dose of cholesterol-4-14C. Chronic physical stress and infrequent feeding, as separate experimental stimuli, both caused cholesterol to shift from the blood plasma at a higher rate and reduced the size of one or both cholesterol body pools (with quick or slow turnover, pools A and B). Physical exercise also reduced fractional cholesterol turnover in pool A. When the two stimuli were combined, i.e. in infrequently fed and chronically stressed rats, the rate of the cholesterol shift from the blood plasma slowed down, the total and irreversible shift of cholesterol from pool A diminished and the production rate in this pool also fell.