Effects of membrane physical parameters on hematoporphyrin-derivative binding to liposomes: A spectroscopic study

Summary Physical parameters of membrane bilayers were studied for their effect on the binding of hematoporphyrin derivative (Hpd), which is used as a sensitizer in photodynamic therapy of cancerous tissues. The purpose of this study was to clarify which parameters were relevant, under physiological conditions, to the selectivity of Hpd binding to cancer cells. Fluorescence spectroscopy was used to measure the relative partitioning of the dye between the lipid and aqueous media. Increasing the microviscosity of the liposomes' membranes by various bilayer additives results in a strong reduction of Hpd binding, to an extent independent of the specific additive. The effect of temperature near the physiological value as well as the effect of cross membrane potential are small. Surface potential does not affect the binding constant, indicating that the binding species does not carry a net electric charge.     

Periodic electric field as a biopolymer conformation switch: a possible mechanism

A theoretical model is proposed to describe the influence of a periodic electric field (PEF) upon a biopolymer. The biopolymer is treated as a classical mechanical system consisting of subsystems (molecular groups) which interact with each other through potential forces. The PEF is treated as a periodic driving force applied to a molecular group. The energy dissipation is considered using the model of fluid (viscous) friction. Arguments for the non-linear character of the friction-velocity dependence caused by the non-Newtonian rheology of a viscous medium are formulated.A forced molecular-group motion is investigated for the situation of a small driving-force period, with oscillations overdamped and a driving force consisting of more than one harmonic. As a result, it is established that the motion always gets to a terminal stage when only a small-scale vibration about some point, X ^*, takes place. The terminal motion is preceded by a transient characterized by the presence of a directional velocity component and so by a drift along a potential profile. the drift goes on until a barrier is met which has a sufficiently large steepness (the barrier height is not important). As a result, the point X ^* may happen to be remote from the conformation potential local minimum (conformational state). The physical reasons for the drift are described.If we consider the small-scale vibration about X ^* in the framework of the hierarchy of scales for intramolecular mobility, it can be regarded as an equilibrium mobility, whereas the drift can be regarded as a functionally important motion, and X ^* as a new conformational state which is realizable only in the presence of the PEF. It may be concluded, as the result of a consistent treatment and neglecting the small-scale vibration, that the conformational potential is modified by adding a linear term (in the one-dimensional case). In this connection, the set of conformational states can both deform (deviation of the positions of minima and their relative depth) and rearrange qualitatively (some minima can vanish and/or new minima can appear). In particular, the transition from one conformation to another one may happen due to rearrangement.     

脱落酸对植物线粒体膜生物物理特性的影响

采用１,６－二苯基－１,３,５－已三乙烯（ＤＰＨ）荧光偏振法和中性红法分别研究了脱落酸（ＡＢＡ）对玉米黄化芽及大豆子叶离体线粒体膜的微粘度（η）、表面电位（ψ）等生物物理特性的影响。结果表明：ＡＢＡ有降低线粒体膜的微粘度及提高线粒体膜的表面电位作用,并导致呼吸速率升高,呼吸控制和氧化磷酸化偶联下降。ＡＢＡ对线粒体膜微粘度的作用具有浓度饱和效应;ＡＢＡ对线粒体膜表面电位的提高作用,因植物不同而有差异,对玉米的作用要大于对大豆的。追踪线粒体Ａ（３５０）值的变化,还证实,ＡＢＡ提高了大豆线粒体的Ａ（３５０）值,即导致大豆线粒体的相互聚集（ａｇｇｒｅｇａｔｉｏｎ）。     

Effect of laser irradiation on microviscosity of aqueous medium in imbibing maize seeds as studied with a spin probe method

A spin probe method was used to study microviscosity of aqueous medium in embryos and endosperm of maize (Zea mays L.) seeds after their irradiation with a Lvov-1 Elektronika laser device. Based on parameters of electron spin resonance (ESR) spectra of nitroxyl radicals (probes) absorbed by imbibing seeds during water uptake, correlation times τ_C were determined for the rotational diffusion of probes in embryos and endosperm of seeds. The τ_C values were found smaller in embryos of irradiated seeds than in untreated seeds; the dependence of τ_C on the duration of seed imbibition was determined. It is concluded that laser irradiation of seeds decreases the microviscosity of aqueous medium in embryo cells and elevates the mobility of the probes. Effect of laser irradiation on τ_C in seed endosperm was less pronounced but also led to the increase in probe mobility.     

Ethylene and flower petal senescence: Interrelationship with membrane lipid catabolism

Accumulated experimental evidence suggests that the decline in the content of membrane components such as phospholipids (PL), is a key event in flower senescence. This loss of membrane integrity can be modulated by ethylene. The aim of this work was to examine the interrelationship between ethylene and one of the products of PL metabolism, diacylglycerol (DAG), during petunia ( Petunia hybrida ) flower senescence. DAG's role was studied using phorbol 12-myristate 13-acetate (PMA), which acts similarly in kinase activation. Our results demonstrate for the first time a senescence-related transient increase in the content of DAG in petunia plasma membranes. The climacteric-like ethylene rise associated with petal wilting appeared in petunia flowers well after PL degradation and DAG increase had commenced. The appearance and peak magnitude of the ethylene rise was enhanced or increased, respectively, by PMA treatment, thereby accelerating appearance and magnitude of all senescence parameters assayed. Conversely, suppression of ethylene action by silver thiosulfate (STS) resulted in retardation of flower wilting, as well as in abolishment of the PMA-enhancing effects on senescence. The results suggest an active role for lipid metabolites like DAG in enhancing flower senescence, through regulation of ethylene production and action, or possible activation of kinases. This sequence of events implies that ethylene is a mediator of flower senescence, rather than a trigger of the process.     

Modulation of Opioid Receptor Binding by Cis and Trans Fatty Acids

In synaptosomal brain membranes, the addition of oleic acid (cis), elaidic acid (trans), and the cis and trans isomers of vaccenic acid, at a concentration of 0.87 mumol of lipid/mg of protein, strongly reduced the Bmax and, to a lesser degree, the binding affinity of the mu-selective opioid [3H]Tyr-D-Ala-Gly-(Me)Phe-Gly-ol ([3H]DAMGO). At comparable membrane content, the cis isomers of the fatty acids were more potent than their trans counterparts in inhibiting ligand binding and in decreasing membrane microviscosity, both at the membrane surface and in the core. However, trans-vacenic acid affected opioid receptor binding in spite of just marginally altering membrane microviscosity. If the receptors were uncoupled from guanine nucleotide regulatory protein, an altered inhibition profile was obtained: the impairment of KD by the fatty acids was enhanced and that of Bmax reduced. Receptor interaction of the delta-opioid [3H](D-Pen2,D-Pen5)enkephalin was modulated by lipids to a greater extent than that of [3H]DAMGO: saturable binding was abolished by both oleic and elaidic acids. The binding of [3H]naltrexone was less susceptible to inhibition by the fatty acids, particularly in the presence of sodium. In the absence of this cation, however, cis-vaccenic acid abolished the low-affinity binding component of [3H]naltrexone. These findings support the membrane model of opioid receptor sequestration depicting different ionic environments for the mu- and delta-binding sites. The results of this work show distinct modulation of different types and molecular states of opioid receptor by fatty acids through mechanisms involving membrane fluidity and specific interactions with membrane constituents.     

切应力对内皮细胞膜微粘度的影响

目的：研究切应力对内皮细胞（EC）膜微粘度的影响。材料和方法：将EC置于脉动循环装置中,分别施加15dyne/cm^2,50dyne/cm^2,30Odyne/cm^2切应力,作用Oh,1h,2h,4h,6h,10h后,利用带偏振器的荧光分光光度计测量膜微粘度,结果：切应力使膜微粘度增加,且切应力越高,膜微粘度增加幅度越大。切应力作用4h,EC膜微粘度升至最高,4h-10h,膜微粘度开始缓慢恢复,但仍比静态对照显著升高,结论：在切应力作用下,EC膜微粘度增加,切应力是AS的致病因素,动脉狭窄处和大中动脉分叉处是AS好发的危险部位,也是防治的重点。     

ESR measurement of time-dependent and equilibrium volumes in red cells

Summary Red cell water volumes were measured using ESR methods during transient osmotic perturbation, and under equilibrium conditions. Cell water contents were determined using the spin label Tempone (2,2,6,6-tetramethyl piperidine-N-oxyl) and the membrane impermeable quencher potassium chromium oxalate. With appropriate corrections for intracellular viscosity and changes in cavity sensitivity, equilibrium cell water measured both by electron spin resonance (ESR) and wet minus dry weight methods gave excellent agreement in solutions from 243–907 mOsm. Intracellular viscosities determined from the Tempone correlation times in the same cells gave values ranging from 9–47 centipoise at 21°C.Osmotically induced transient volume changes were measured using Tempone and an ESR stopped-flow configuration. The Tempone response time was estimated at 17 msec compared to 250–350 msec for normal water relaxations. Nonlinear least square solutions to the Kedem-Katchalsky equations including a correction for the finite Tempone permeability gave 0.029 and 0.030 cm/sec for the osmotic permeability of RBCs in swell and shrink experiments, respectively. In stopped-flow experiments accurate water flux data are obtained very soon after challenging cells and do not require baseline subtractions. These results represent significant improvements over conventional light scattering techniques which necessitate corrections for long lasting optical artifacts (200–300 msec), and baseline drifts.     

Modulation of membrane composition of swine vascular smooth muscle cells by homologous lipoproteins in culture

Swine vascular smooth muscle cells were exposed to homologous low-density or high-density lipoprotein fractions for 24 h. Total cell membranes were isolated from the post-nuclear supernatant of the cell homogenates, fractionated by sucrose density gradient centrifugation and characterized by enzyme assays. The membrane fraction with the lowest density was enriched in plasma membrane marker enzymes. Cholesterol analysis showed that cells exposed to low-density lipoprotein had higher cholesterol-to-protein ratios in total cells, total cell membranes and individual membrane fractions than had the cells exposed to high-density lipoproteins. Cholesterol-to-phospholipid ratios of the plasma membrane-enriched fraction from cells exposed to low-density lipoprotein were higher than the same membrane fraction of cells exposed to high-density lipoprotein. Studies with iodinated lipoproteins showed that these compositional changes could not be due to lipoprotein contamination. Membrane microviscosity was determined by fluorescence depolarization with diphenylhexatriene and the microviscosity of the plasma membrane-enriched fraction was different in the cells exposed to the two different lipoprotein fractions. This difference in membrane microviscosity was significant only when the medium cholesterol content was 40 μg per ml or greater; cells exposed to low-density lipoprotein gave membranes with higher microviscosity.These results demonstrate that the properties of vascular smooth muscle cell membranes are influenced by exposure of the cells to homologous lipoprotein fractions.