Kappa but not delta or mu opioid receptors form homodimers at low membrane densities

Opioid receptors (ORs) have been observed as homo- and heterodimers, but it is unclear if the dimers are stable under physiological conditions, and whether monomers or dimers comprise the predominant fraction in a cell. Here, we use three live-cell imaging approaches to assess dimerization of ORs at expression levels that are 10–100 × smaller than in classical biochemical assays. At membrane densities around 25/µm2, a split-GFP assay reveals that κOR dimerizes, while µOR and δOR stay monomeric. At receptor densities < 5/µm2, single-molecule imaging showed no κOR dimers, supporting the concept that dimer formation depends on receptor membrane density. To directly observe the transition from monomers to dimers, we used a single-molecule assay to assess membrane protein interactions at densities up to 100 × higher than conventional single-molecule imaging. We observe that κOR is monomeric at densities < 10/µm2 and forms dimers at densities that are considered physiological. In contrast, µOR and δOR stay monomeric even at the highest densities covered by our approach. The observation of long-lasting co-localization of red and green κOR spots suggests that it is a specific effect based on OR dimerization and not an artefact of coincidental encounters.

The exocyst complex regulates C. elegans germline stem cell proliferation by controlling membrane Notch levels

ABSTRACT The conserved exocyst complex regulates plasma membrane-directed vesicle fusion in eukaryotes. However, its role in stem cell proliferation has not been reported. Germline stem cell (GSC) proliferation in the nematode Caenorhabditis elegans is regulated by conserved Notch signaling. Here, we reveal that the exocyst complex regulates C. elegans GSC proliferation by modulating Notch signaling cell autonomously. Notch membrane density is asymmetrically maintained on GSCs. Knockdown of exocyst complex subunits or of the exocyst-interacting GTPases Rab5 and Rab11 leads to Notch redistribution from the GSC-niche interface to the cytoplasm, suggesting defects in plasma membrane Notch deposition. The anterior polarity (aPar) protein Par6 is required for GSC proliferation, and for maintaining niche-facing membrane levels of Notch and the exocyst complex. The exocyst complex biochemically interacts with the aPar regulator Par5 (14-3-3ζ) and Notch in C. elegans and human cells. Exocyst components are required for Notch plasma membrane localization and signaling in mammalian cells. Our study uncovers a possibly conserved requirement of the exocyst complex in regulating GSC proliferation and in maintaining optimal membrane Notch levels.

The new molecular targets for antidepressants

The efficacy of depressive disorders treatment is insufficient. It is explained by an incomplete understanding of both pathogenesis of depression and antidepressants mechanism action. An improvement of the treatment efficacy of depression disorders is closely associated with complete knowledge of the pathogenesis of disorders and antidepressant mechanism of action. The effect produced by the first line of antidepressants prescribed currently in the clinical practice includes the accumulation of monoamines and prolonged activation of their membrane receptors. However, a decrease in the membrane receptors density evoked by prolonged activation of monoaminergic receptors is counteracted by the second line of antidepressant activity. It is associated with the expression of inducible regulatory protein S100A10 (p11) and its partners. In this review, the authors examined the structure and function of protein p11, its interaction with such proteins as annexin A2, Ahnak, chromatinremodeling factor SMARCA3. The authors analyzed the influence of p11 on the membrane density of serotonin 5-HT1B and 5-HT4 receptors, metabotropic glutamate receptors 5, voltage-dependent potassium Kv3, and calcium Cav1.2 and 1.3 channels, that play an important role in both the effect of antidepressants and the pathogenesis of depression disorders. A systematic literature search was conducted in Scopus, Web of Science, MedLine, elibrary, and other databases.

COMPORTAMENTO DE FTALOCIANINA LIPOSSOMAL NO CONTEXTO DA DINÂMICA MOLECULAR

Since the early 1990s, hydrated phospholipid bilayers have been studied using computational modeling methods. In this context, the simulation of the behavior of lipid biomembranes is a promising area, not only for its applications in the understanding of cell membranes, but also for its application to several drug delivery systems widely used and studied during the last decades. Is this worj performed computational simulations of lipid membranes added or not with cholesterol and zinc phthalocyanine, to obtain membrane density values, zinc phthalocyanine side diffusion, system and drug atomic mobility and density maps of the system using GROMACS. Liposomes with suitable ratio between free cholesterol and esterified cholesterol and phospholipids showed encapsulation rates of approximately 80%. In conclusion, The interaction of photosensitizers with free cholesterol influences their spatial disposition in the bi-layers and is directly related to the cell mortality rate.

Tensile Properties of Three Selected Collagen Membranes

Background. Biological barriers are commonly used to treat alveolar bone defects and guide tissue regeneration. Understanding the biological and mechanical properties of the available membranes is crucial for selecting the one that is optimal for enhancing clinical outcomes. Purpose. To evaluate the mechanical behavior of three different collagen membranes to increasing tensile force in dry and wet conditions. Materials and Methods. Three commercially collagen membranes were selected for analysis: Bio-Gide® (Geistlich Biomaterials, Baden-Baden, Germany), Remaix™ (RX; Matricel GmbH, Herzogenrath, Germany), and Ossix Plus® (Datum Dental Biotech, Lod, Israel). Increasing tensile forces were applied on 10 dry and wet membranes of standard size via a loading machine. Force and extension values were acquired up to maximum load before failure, and maximum stress, maximum extension, and amount of energy needed for membrane tearing were analyzed. Membranes’ densities were also calculated. Results. The Remaix membrane exhibited the highest values of maximum load tensile strength, maximum extension, and maximum energy required for membrane tearing, followed by Bio-Gide. Ossix Plus had the lowest scores in all these parameters. Dry membranes had the highest scores for all parameters except extension. Membrane density was directly and significantly correlated with all tested parameters. Conclusions. The study was undertaken to provide clinicians with data upon which to base the selection of collagen membranes in order to achieve optimal clinical results. It emerged that the mechanical properties of dry and wet collagen membranes were significantly different from one another. Among the 3 tested membranes, Remaix exhibited higher performance results in all the mechanical tests. Collagen membrane density seems to have a significant influence upon mechanical resistance. These findings may also guide manufacturers in improving the quality of their product.

Study of Solvent Mixture of Aqua destillata–Acetone in the Making of Cellulose Propionate Membrane

<p>In this article we will discuss the solubility test of cellulose propionate on various ratio variations of aqua destillata–acetone. Previously cellulose propionate was dispersed into a solvent mixture of aqua destillata-acetone. Variation in volume ratio of aqua destillata–acetone was 4: 1; 3: 1; 2: 1; 1: 2; 1: 3, and 1: 4. The mixture is stirred for 48 h and filtered. The solid was then put into a mold with a sintering technique at a temperature of 100^oC for 5-10 minutes. Membrane characterization includes solubility parameters (δ_mix), density using picno meter and calculation of sample dimensions, and swelling index. The results of the calculation of solubility parameters (δ_mix) solvent mixture of aqua destillata–acetone (1: 4) close to δ cellulose acetate (12.47). Differences in membrane density using picno meter and calculations in dimensions indicate the presence of cavities or pores in the membrane. Difference in density value of both calculations occurs in the membrane with a mixture of aqua destillata–acetone (1: 3). The highest hydrophobicity properties were obtained in the ratio of solvents of destillata–acetone (1: 4) with the smallest swelling index (48.14%).</p>

Nonlinear Oscillations of Hyperelastic Annular Membranes With Varying Density

This research presents the mathematical modeling for the nonlinear oscillations analysis of a pre-stretched hyperelastic annular membrane with varying density under finite deformations. The membrane material is assumed to be homogeneous, isotropic, and neo-Hookean and the variation of the membrane density in the radial direction is investigated. The membrane is first subjected to a uniform radial traction along its outer circumference and the stretched membrane is fixed along the outer boundary. Then the equations of motion of the pre-stretched membrane are derived. From the linearized equations of motion, the natural frequencies and mode shapes of the membrane are obtained analytically. The vibration modes are described by hypergeometric functions, which are used to approximate the nonlinear deformation field using the Galerkin method. The results are compared with the results evaluated for the same membrane using a nonlinear finite element formulation. The results show the influence of the stretching ratio and varying density on the linear and nonlinear oscillations of the membrane.

Corneal Backscatters as an Objective Index for Assessing Fuchs’ Endothelial Corneal Dystrophy: A Pilot Study

Purpose. To provide an objective, quantitative approach for monitoring Fuchs’ endothelial corneal dystrophy (FECD), with Scheimpflug imaging. Design. This is a retrospective case-control pilot study. Methods. The study group consisted of 53 eyes in 27 patients diagnosed with FECD, with normal subjects paired as control. Main outcome measures were corneal thickness, morphological patterns on densitograms, and indices of corneal density including the average area density (mean AD) and the average ratio of Descemet’s membrane density versus area density (DM/AD) in Pentacam Scheimpflug images. Results. There were no significant differences in age and corneal thickness between FECD and normal groups. Morphologically, hanging-hammock patterns were noted on the densitograms of FECD patients, which were different from the high-back chair patterns in normal subjects. Quantitatively, mean AD and DM/AD were both elevated in FECD patients as compared with normal subjects (P=0.01 and 0.025, resp.). In addition, FECD patients with corneal edema had significantly higher mean AD (P=0.018) than those without corneal edema. Conclusions. This pilot study shows that Pentacam system provides an objective, quantitative way to approach FECD corneas. It can assist ophthalmologists in detecting the early change and in monitoring disease progression of FECD. Further studies are needed to consolidate the findings.