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Synaptic strength depends on the number of cell-surface neurotransmitter receptors in dynamic equilibrium with intracellular pools. Dysregulation of this homeostatic balance occurs, for example in myasthenia gravis, an autoimmune disease characterized by a decrease in the number of postsynaptic nicotinic acetylcholine receptors (nAChRs). Monoclonal antibody mAb35 mimics this effect. Here we use STORM nanoscopy to characterize the individual and ensemble dynamics of monoclonal antibody-crosslinked receptors in the clonal cell line CHO-K1/A5, which robustly expresses adult muscle-type nAChRs. Antibody labeling of live cells results in 80% receptor immobilization. The remaining mobile fraction exhibits a heterogeneous combination of Brownian and anomalous diffusion. Single-molecule trajectories exhibit a two-state switching behavior between free Brownian walks and anticorrelated walks within confinement areas. The latter act as permeable fences (~34 nm radius, ~400 ms lifetime). Dynamic clustering, trapping, and immobilization also occur in larger nanocluster zones (120–180 nm radius) with longer lifetimes (11 ± 1 s), in a strongly cholesterol-sensitive manner. Cholesterol depletion increases the size of the clustering phenomenon; cholesterol enrichment has the opposite effect. The disclosed high proportion of monoclonal antibody-crosslinked immobile receptors, together with their anomalous, cholesterol-sensitive diffusion and clustering, provides new insights into the antibody-enhanced antigenic modulation that leads to physiopathological internalization and degradation of receptors in myasthenia. (Figure presented.). Fil: Mosqueira, Alejo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Biomédicas; Argentina Fil: Camino, Pablo A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Biomédicas; Argentina Fil: Barrantes, Francisco Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Biomédicas; Argentina

Lipids and proteins in the plasma membrane are laterally heterogeneous and formalised as lipid rafts featuring unique biophysical properties. However, the self-assembly mechanism of lipid raft cannot be revealed even its physical properties and components were determined in specific physiological processes. In this study, two-photon generalised polarisation imaging and fluorescence correlation spectroscopy were used to study the fusion of lipid rafts through the membrane phase and the lateral diffusion of lipids in living breast cancer cells. A self-assembly model of lipid rafts associated with lipid diffusion and membrane phase was proposed to demonstrate the lipid sorting ability of lipid rafts in the plasma membrane. The results showed that the increased proportion of slow subdiffusion of GM1 -binding cholera toxin B-subunit (CT-B) was accompanied with an increased liquid-ordered domain during the β-estradiol-induced fusion of lipid rafts. And slow subdiffusion of CT-B was vanished with the depletion of lipid rafts. Whereas the dialkylindocarbocyanine (DiIC18 ) diffusion was not specifically regulated by lipid rafts. This study will open up a new insight for uncovering the self-assembly of lipid rafts in specific pathophysiological processes.

Growing evidence shows that GM1 ganglioside is involved in amyloid deposition and toxicity. By means of real-time single particle tracking, we show that amyloid oligomers and aggregates formed by A beta 1-42 and amylin, two peptides associated, respectively, with the development of Alzheimer's disease and type II diabetes, interact with GM1 and decrease dramatically its lateral diffusion on the plasma membrane of living neuroblastoma cells. The confinement of GM1, a constituent of membrane rafts involved in neuroprotection, at the level of both types of amyloid aggregates can interfere with cell signaling pathways and contribute to the loss of neuroprotection. (C) 2013 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.

The centripetal movement of fluorescein and fluorescein-labelled dextrans (4 to 150 kD) from sclera or cut edge of the cornea was determined in isolated rabbit corneas at 4 and 24 h. Corneas were divided into 5.5 mm diameter central core, inner 5.5 to 8 mm donut, 8 to 12 mm peripheral donut and, where applicable, scleral rim. For all molecules greater than sodium fluorescein (376 D) tracer concentrations in the 5.5 mm core and the 5.5 to 8 mm donut were equal. Without sclera rim, the more central portions of the cornea (5.5 mm core and 5.5 to 8 mm donut) had tracer concentrations equal to those of corneas-with-sclera for all tracers greater than 10 kD. The tracer concentrations in the central cornea were the same in the presence or absence of sclera. The data indicate a physiological barrier to the lateral diffusion of molecules greater than 10 kD between the peripheral and more central cornea.

Phosphatidylinositol 4,5-bisphosphate (PIP2)-mediated signalling is a new and rapidly developing area in the field of cellular signal transduction. With the extensive and growing list of PIP2-sensitive membrane proteins (many of which are ion channels and transporters) and multiple signals affecting plasma membrane PIP2 levels, the question arises as to the cellular mechanisms that confer specificity to PIP2-mediated signalling. In this review we critically consider two major hypotheses for such possible mechanisms: (i) clustering of PIP2 in membrane microdomains with restricted lateral diffusion, a hypothesis providing a mechanism for spatial segregation of PIP2 signals and (ii) receptor-specific buffering of the global plasma membrane PIP2 pool via Ca2+-mediated stimulation of PIP2 synthesis or release, a concept allowing for receptor-specific signalling with free lateral diffusion of PIP2. We also discuss several other technical and conceptual intricacies of PIP2-mediated signalling.

By directly imaging the photoluminescence of the samples, we observe strong anisotropic lateral diffusion of photogenerated carriers in InGaN/GaN quantum-wells structures. For quantitative interpretation of the phenomenon, the ambipolar diffusion of carriers in such structures is calculated using the two-dimensional drift-diffusion equation when the huge piezoelectric field in the strained InGaN/GaN quantum wells is taken into account. Very good agreement between theory and experiment is achieved. Our results show that the strong piezoelectric field and crystalline direction dependence of the carrier mobility are responsible for the enhancement and anisotropy of carriers' lateral diffusion, respectively. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

ever, depend on the validity and best estimation of key hydrological as well as nutrient fate and transport paAccurate characterization of lateral transport components is an imrameters. portant step toward a more quantitative assessment of the fate and

Zn–Sn–O (ZTO) thin film transistors (TFTs) were fabricated with a Cu source/drain electrode. Although a reasonably high mobility (μFE) of 13.2 cm2/Vs was obtained for the ZTO TFTs, the subthreshold gate swing (SS) and threshold voltage (Vth) of 1.1 V/decade and 9.1 V, respectively, were inferior. However, ZTO TFTs with Ta film inserted as a diffusion barrier, exhibited improved SS and Vth values of 0.48 V/decade and 3.0 V, respectively as well as a high μFE value of 18.7 cm2/Vs. The improvement in the Ta-inserted device was attributed to the suppression of Cu lateral diffusion into the ZTO channel region. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This mini-review focuses on the utilization of pulsed magnetic field gradients to measure diffusional motion in systems of macroscopically oriented lipid bilayers. The NMR diffusion technique is pr ...

We have performed a systematic analysis of models explaining the mechanisms of the intracellular biosecretory transport. The models assessed include not only those based on one mechanism (the dissociation model (and its individual case, the vesicular model), the progression model (and its individual cases, the cisterna maturation/progression and the carrier maturation models), and the lateral diffusion model (and its individual case, the bolus model), but also combined models of transport (the percolating-vesicles model and the synthetic model), including several transport mechanisms. Most of these models are not able to explain recent data on the evolution of genes involved in intracellular transport and Golgi evolution. The carrier maturation model proposing that fusion of the large cargo domain with the distal (closer to the plasmalemma) compartment precedes fission of the domain from the proximal compartment exhibits the best performance in correlation with the available information on evolution of the biosecretory pathway.

[EN] Viral movement proteins exploit host endomembranes and the cytoskeleton to move within the cell via routes that, in some cases, are dependent on the secretory pathway. For example, melon necrotic spot virus p7B, a type II transmembrane protein, leaves the endoplasmic reticulum (ER) through the COPII-dependent Golgi pathway to reach the plasmodesmata. Here we investigated the sequence requirements and putative mechanisms governing p7B transport through the early secretory pathway. Deletion of either the cytoplasmic N–terminal region (CR) or the luminal C–terminal region (LR) led to ER retention, suggesting that they are both essential for ER export. Through alanine-scanning mutagenesis, we identified residues in the CR and LR that are critical for both ER export and for viral cell-to-cell movement. Within the CR, alanine substitution of aspartic and proline residues in the DSSP b–turn motif (D7AP10A) led to movement of discrete structures along the cortical ER in an actin-dependent manner. In contrast, alanine substitution of a lysine residue in the LR (K49A) resulted in a homogenous ER distribution of the movement protein and inhibition of ER–Golgi traffic. Moreover, the ability of p7B to recruit Sar1 to the ER membrane is lost in the D7AP10A mutant, but enhanced in the K49A mutant. In addition, fluorescence recovery after photobleaching revealed that K49A but not D7AP10A dramatically diminished protein lateral mobility. From these data, we propose a model whereby the LR directs actin-dependent mobility toward the cortical ER, where the cytoplasmic DSSP b–turn favors assembly of COPII vesicles for export of p7B from the ER., We are grateful to C. Hawes (Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Headington, Oxford, UK) and V. V. Dolja (Department of Botany and Plant Pathology and Center for Genome Research and Biocomputing, Oregon State University, Corvallis, OR, USA) for providing the Sar1-YFP construct and some fluorescent-tagged organelle markers, respectively. We would like to thank F. Aniento (Departmento de Bioquimica y Biologia Molecular, Facultad de Farmacia, Universidad de Valencia, Burjassot, Valencia, Spain) and E. Rojo (Departament of Plant Molecular Genetics, Centro Nacional de Biotecnologia, Consejo Superior de Investigaciones Cientificas, 28049 Madrid, Spain) for critical reading and valuable comments on this manuscript. This work was funded by grant BIO2011-25018 from the Spanish Departmento Governmental de Investigaciones Cientificas y Tecnologicas and Prometeo Program GV2011/003 from the Generalitat Valenciana. J.A.N. and M. S. are the recipients of a postdoctoral contract and a PhD fellowship from the Ministerio de Educacion y Ciencia of Spain. We thank L. Corachan for her technical assistance.

The lateral mixing of water in a shallow rectangular tank (length 225 cm, width 56.5 cm, depth 15 cm) under the action of bottom-stir plugs has been studied. The process has been measured and video-recorded, using an acid-base reaction with indicator to show the flow patterns. It is concluded that in spite of the very low depth/width ratio in the tank, lateral mixing can be achieved quite efficiently using certain configurations of plugs which promote lateral circulation. With the best configuration, a mixing time of about 3.5 min could be achieved using either 4 or 6 plugs. The specific power dissipation rate was very low (0.0044 W/kg). The mixing time was essentially the same with 4 or 6 plugs provided the total gas flow to the plugs was the same in the two cases. Tests with intermittent blowing of the plugs did not show any improvements over steady operation. On a etudie le melange lateral d'eau dans un reservoir rectangulaire peu profond (longeur 225 cm, largeur 56,5 cm, profondeur 15 cm) sous l'action de bouchons agites situes en fond de reservoir. On a mesure et enregistre le procede par video, en utilisant une reaction acide-base avec un indicateur pour montrer les profils d'ecoulement. On a conclu que malgre le tres faible rapport profondeur/largeur dans le reservoir, le melange lateral pouvait ětre realise assez efficacement en employant certaines configurations de bouchons qui favorisent la circulation laterale. Avec la meilleure configuration, on peut realiser un temps de melange d'environ 3.5 min avec 4 ou 6 bouchons. La consommation de puissance specifique est tres faible (0,0044 W/kg). Le temps de melange est essentiellement le měme avec 4 ou 6 bouchons a condition que le debit de gaz total applique aux bouchons soit le měme dans les deux cas de figure. Des essals menes avec un debit de gaz Intermittent dans les bouchons ne montrent aucune amelioration par rapport au fonctionnement en regime stationnaire.

Appropriate Rochow contact masses have been investigated by the spatial resolution techniques SEM–EDX and SAM–AES. The results gave evidence of the existence and the catalytic action of (X-ray)-amorphous copper–silicon (Cu–Si) surface species, i.e. extremely highly dispersed particles or two-dimensional species. The well-known Rochow promoter zinc seems to act as a moderator rather than as a real accelerator. It ensures a stable rate for the reaction by neutralizing the detrimental action of silicon impurities. The silicon impurities make the whole of the silicon surface reactive and in this way cause a general blockade of the silicon surface by inactive copper species. Zinc localizes the reaction. The silicon surface remains partly free, and active Cu–Si surface species can be formed by lateral diffusion of copper onto the silicon surface that is still free. © 1997 by John Wiley & Sons, Ltd.

Phospholipid vesicles exhibit a natural tendency to fuse and assemble into a continuous single bilayer membrane on silica and several other substrate materials. The resulting supported membrane maintains many of the physical and biological characteristics of free membranes, including lateral fluidity. Recent advances, building on the supported membrane configuration, have created a wealth of opportunities for the manipulation, control, and analysis of membranes and the reaction environments they provide. The work reviewed in this Account, which can be broadly characterized as the science and technology of membrane patterning, contains three basic components: lateral diffusion control (barriers), membrane deposition techniques (microarrays), and electric field-induced lateral reorganization. Collectively, these preparative and analytical patterned membrane techniques offer a broad experimental platform for the study and utilization of lipid membranes.

Salmonella typhimurium 1195 mutant bacteria were allowed to produce clusters of lipopolysaccharide with new, wild-type specificity over the export sites. Ferritin-labeling experiments showed that the lipopolysaccharide diffuses away from the export sites at 37 °C and is found dispersed on the cell surface, whereas at 0 °C it remains immobile. The density of lipopolysaccharide molecules on the bacterial surface, measured as number of lipopolysaccharide molecules per μm2, or as percentage of the bacterial surface covered by lipopolysaccharide was determined in two wild-type S. typhimurium strains and one mutant strain, which was grown under conditions either permissive or nonpermissive for the formation of wild-type lipopolysaccharide. There are 0.7—1.0 × 105 lipopolysaccharide molecules per μm2 surface area. About 15—25% of the bacterial surface was found to be covered by lipopolysaccharide. The mean intermolecular distance at hypothetical uniform distribution of lipopolysaccharide was calculated to be in the range of 3—4 nm. It was of no consequence to the lipopolysaccharide surface density whether the mutant strain produced wildtype or mutant lipopolysaccharide. An estimate of the lateral diffusion constant D (D∼ 3 × 10−13 cm2/s) of lipopolysaccharide in the outer membrane was made from earlier published data [2]. Possible reasons for the low order of magnitude of D, based on the observed surface density, are discussed.

Both quantitative and qualitative aspects of the interpretation of fluorescence photobleaching recovery experiments as typically practised to obtain information on lateral diffusion processes in cell membranes are called into question in view of the polarized nature of the laser light sources routinely employed. Protocols which will eliminate the effects elicited under these conditions by any concurrent slow rotational diffusion are delineated.

Fusion of influenza virus with human erythrocytes at pH 5.2 was followed by fluorescence microscopy using a cooled slow-scan CCD camera. The high sensitivity of the CCD permits repetitive digital imaging of the same cells with minimal photobleaching. The experimental conditions were such that only a small number of virus particles were adsorbed per cell. Quantitative analysis of the data indicated that for most cells only a single fusion event took place. This was, however, sufficient to cause haemolysis within 30 min at 20-22 degrees C for about 60% of cells. There was a highly variable time lag between fusion and haemolysis. The lateral diffusion coefficient of virus particles on the cell surface when bound at pH 7.4 was less than 2 x 10(-13) cm2.s-1. The technique should be of value for more detailed studies of the dynamics of viral and other membrane fusion events.

The lateral silver diffusion starting from a photodoped edge in amorphous Ge25 Se75 layers is studied by optical means. It is shown that the lateral diffusion is photoinduced. Without exposure a diffusion could not be detected with the microspectrophotometer whereas under illumination the silver covers distances in the millimetre range. Transparency profiles reveal a step-like diffusion front which is characteristic for a tarnishing process. It is shown that the diffusion depends on the history of the sample, especially on the pre-exposure. The consequences for the use of germanium chalcogenide as an anorganic resist are shortly discussed. Mit optischen Methoden wird die laterale Silberdiffusion, die in amorphen Ge25 Se75-Schichten von einer photodotierten Kante ausgeht, untersucht. Es wird gezeigt, das die laterale Diffusion ein photoinduzierter Effekt ist. Ohne Belichtung kann mit dem Mikrospektrophotometer keine laterale Diffusion nachgewiesen werden, wahrend bei Belichtung vom Silber Wegstrecken bis in den Millimeterbereich zuruckgelegt werden. Die Transparenzprofile weisen eine stufenartige Diffusionsfront aus, was fur einen Anlaufprozes charakteristisch ist. Es wird gezeigt, das die Diffusion von der Probenvorgeschichte, speziell von einer Vorbelichtung, abhangig ist. Die Kon-sequenzen fur den Einsatz von Germaniumchalkogenidschichten als anorganischer Resist werden kurz diskutiert.

Taking advantage of the extremely slow lateral diffusion of proteins on Rana amurensis egg surface (Xu et al., 1984), it was possible to make a sharp concentric ring pattern on the egg surface by photobleaching of the fluorescein-labelled egg surface. The shape change of the pattern reveals the movement of the egg surface. The surface, even in front of the furrow tip, is drawn towards the furrow centre. The furrow tip differentiates into border and central lines as shown by the distribution of surface protrusions. Between the border and central lines the nascent membrane inserts while the width of furrow tip increases to nearly 100 microns.

Current knowledge of lipid and protein diffusion rates in homogeneous, fluid, artificial bilayers is reviewed and the ability of current theory to account for these rates is evaluated as a reference for understanding lateral diffusion in biomembranes. Experimental evidence on the effects of increasing protein concentration on the lateral diffusion of membrane lipids and proteins is summarized to provide a qualitative description of the situation in biomembranes. Lipid bilayersLateral diffusionMembrane proteinsFluorescent probesPhotobleaching

The role of plastoquinone as a mobile redox carrier linking photosystem II and the cytochrome b6−f complex is considered. It is proposed that plastoquinone is located primarily within the fluid bilayer-midplane region of the thylakoid membrane and thus can move laterally at very fast rates corresponding to a microscopic diffusion coefficient of 10−6 cm2·s−1. Because of the presence of integral proteins the diffusion path will be tortuous and extended, giving rise to a sub-macroscopic diffusion coefficient which is lower than the above value. Even so it is concluded that within the half-time for electron donation to the cytochrome b6−f complex there is adequate time for plastoquinone to diffuse over a distance equivalent to the radius of a granum membrane.

Cells are capable of overcoming the randomizing effect of lateral diffusion in order to regionally differentiate their surfaces. Such local structural specializations are of major significance to cellular function. In some cases, they may be explained by diffusion rates that are insufficient to completely randomize surface gradients over biologically relevant times scales. However, in other cases, absolute and permanent regionalizations are also observed. Mechanistically, the problem is analogous to equilibrium across a dialysis bag: either an absolute barrier exists or the chemical potential between two adjacent regions must be equal. The interactive nature of the system, where localizations of one component lead to localization of others, are also considered here.

A simple method for isolation and fluorescence labelling of Leydig cells (L-cells) from rat testes was developed. Lateral diffusion coefficients of both lipid and protein membrane fluorescent probes were measured by the method of fluorescence recovery after photobleaching (FRAP). Age-dependent changes in diffusibility of membrane lipids and proteins were discovered.

Summary. A method of exposing seedlings of Norway spruce (Picea abies (L.) Karst.) to 14CO2 is described. Within the 1st hr alter 14CO2 exposure, no translocation of the 14C out of the treated branch could be observed. After a 24-hr period, however, the 14C in dormant seedlings had been translocated basipetally to part of the root system only, with no lateral diffusion of the 14C-compounds in the stem. About a week after exposure, both symplastic and apoplastic patterns of translocation had caused a more uniform distribution of 14C. In seedlings at active internode elongation, the translocation patterns were fundamentally identical to those in dormant seedlings, but the active shoot growth had led to a more uniform distribution of the 14C. Simazine at 20 ppm had apparently stimulated both the photofixation of 14CO2 and the rate of translocation of the 14C-assimilates. At 30 ppm, however, simazine had blocked the translocation of nutrients to the roots. On the other hand, the 14CO2 uptake was not influenced. The simazine incubation had apparently no influence on the synthesis of cationic photosynthate. Resume. L'auteur decrit une methode d'exposition de ptantules de sapin de Norvege (Picea abies (L.) Karst.) au 14CO2. Dans l'heure qui suit l'exposition au 14CO2; aucune migration du 14C en dehors de la branche traitese n'a pu etre observee. Toutefois, apres 24 heures, le 14C a ete, dans les plantules etat de repos vegetatif transporte dans le sens basipete vers une prartion seulement du systeme radiculaire, sans diffusion laterale de composes du 14C dans la tige aerienne. Environ une semaine apres l'exposition, les systemes symplastique et apoplastique de migration ont provoque une distribution plus uniforme du 14C. Dans les plantules ou se produisait une elongation active des entrenoeuds, les systemes de migration furent fondamentalement identiques a ceux decrits pour les plantules au repos, mais la croissance active de I'appareil acrien provoqua une distribution plus uniforme du 14C. La simazine a 20 ppm stimula apparcment a la fois la photofixation du 14C et le taux de migration des metabolites contenant du 14C. Toutefois a 50 ppm la simazine bloqua la migration des substances nutritives vers les racines. Parailleurs, l'absorption du 14CO2 ne fut pas influencee. L'intoxication par la simazine, n'eut pas apparemment d'influence sur la synthese du compose photosynthetique cathionique. Zusammenfassung. Es wird eine Methode beschrieben, die es ermoglicht, die Keimpflanzen von Fichte (Picea abies (L.) Karst.) 14CO2 auszusetzen. Wahrend der ersten Stunden nach 14CO2-Einwirkung konnte keine Translokation von 14C aus dem behandelten Zweig beobachtet werden, Nach 24 Stunden war jedoch 14C in den dormanten Keimpflanzen basipetal in Teile des Wurzelsystems transportiert worden, wahrend keine laterale Diffusion von 14C-Verbindungen im Stiel erfolgte. Ungefahr eine Woche nach der 14CO2-Einwirkung hatten sowohl symplastische als auch apoplastischc Translokation eine etwas allgemeinere Verteilung von 14C bewirkt. In Keimpflanzen mit aktivem Langenwaclistum entsprach die Translokation grundsatzlich der bei dormanten Keimpfianzen beschriebenen, doch war die Verteilung von 14C infolge des Sprosswachstums etwas allgemeiner. 20 ppm Simazin hatten offensichtUch sowohl die Photoflxlerung von 14CO2 als auch die Translokatiomrate von 14C-Assimilatcn stimuliert. 50 ppm Simazin blockierten jedoch die Translokation von Assimilaten in die Wurzehi, wahrend die 14CO2-Aufnahme nicht beeinflusst worden war. Simazin hatte offensichtlich keinen Einfluss auf die Synthese kationischer Photosynteseprodukte.

Kinetics and mechanisms of reactions of HgI2, HgBrI, or HgBr2 with CuI were studied in the solid state. Mercury(II) halides react via vapor phase, and reactions proceed through counter diffusion of Cu+ and Hg2+. X-Ray and chemical analyses indicate that powdered Cul gives Cu2HgI4 when mixed with HgI2 and a mixture of Cu2HgI4 and CuBr when mixed with HgBrI. CuI and HgBr2 react differently in different molar ratios. In a 1:2 molar ratio mixture of CuI and HgBr2, a new product CuHgBr3 and HgBrI are obtained. Data for lateral diffusion best fit the equation Xn=kt where X is the thickness of product layer at time t, and n and k are const. Formation of solid solutions among reactant and product phases is also noted.