Subcellular distribution of membrane lipids revealed by freeze-fracture electron microscopy

Cell membranes are composed of a large variety of lipids and proteins. While the localization and function of membrane proteins have been extensively investigated, the distribution of membrane lipids, especially in the non-cytoplasmic leaflet of organelle membranes, remains largely unknown. Fluorescent biosensors have been widely used to study membrane lipid distribution; however, they have some limitations. By utilizing the quick-freezing and freeze-fracture replica labeling electron microscopy technique, we can uncover the precise distribution of membrane lipids within cells and assess the function of lipid-transporting proteins. In this review, I summarize recent progress in analyzing intracellular lipid distribution by utilizing this method.

Design of Liposomes Carrying HelixComplex Snail Mucus: Preliminary Studies

In recent decades liposomes have been used in different field thanks to their ability to act as a vehicle for a wide range of biomolecules, their great versatility and their easy production. The aim of this study was to evaluate liposomes as a vehicle for the actives present in the HelixComplex (HC) snail mucus for topical delivery. Liposomes composed of a mixture of phosphatidylcholine, cholesterol and octadecylamine were prepared with and without HC (empty liposomes) and their biological efficacy was tested by evaluating cell viability and migration. HC-loaded liposomes (LHC) were stable throughout 60 days of observation, and showed interesting effects on wound healing reconstitution. In particular, we observed that 25 µg/mL LHC were already able to induce a higher cell monolayer reconstitution in comparison to the untreated samples and HC treated samples after only 4 h (28% versus 10% and 7%, p = 0.03 and p= 0.003, respectively). The effect was more evident at 24 h in comparison with the untreated control (54% versus 21.2% and 41.6%, p = 0.006 and p = NS, respectively). These results represent a preliminary, but promising, novelty in the delivery strategy of the actives present in the HelixComplex mucus.

Xylem Surfactants Introduce a New Element to the Cohesion-Tension Theory

Vascular plants transport water under negative pressure without constantly creating gas bubbles that would disable their hydraulic systems. Attempts to replicate this feat in artificial systems almost invariably result in bubble formation, except under highly controlled conditions with pure water and only hydrophilic surfaces present. In theory, conditions in the xylem should favor bubble nucleation even more: there are millions of conduits with at least some hydrophobic surfaces, and xylem sap is saturated or sometimes supersaturated with atmospheric gas and may contain surface-active molecules that can lower surface tension. So how do plants transport water under negative pressure? Here, we show that angiosperm xylem contains abundant hydrophobic surfaces as well as insoluble lipid surfactants, including phospholipids, and proteins, a composition similar to pulmonary surfactants. Lipid surfactants were found in xylem sap and as nanoparticles under transmission electron microscopy in pores of intervessel pit membranes and deposited on vessel wall surfaces. Nanoparticles observed in xylem sap via nanoparticle-tracking analysis included surfactant-coated nanobubbles when examined by freeze-fracture electron microscopy. Based on their fracture behavior, this technique is able to distinguish between dense-core particles, liquid-filled, bilayer-coated vesicles/liposomes, and gas-filled bubbles. Xylem surfactants showed strong surface activity that reduces surface tension to low values when concentrated as they are in pit membrane pores. We hypothesize that xylem surfactants support water transport under negative pressure as explained by the cohesion-tension theory by coating hydrophobic surfaces and nanobubbles, thereby keeping the latter below the critical size at which bubbles would expand to form embolisms.

Reversible Leaf Xylem Collapse: A Potential "Circuit Breaker" against Cavitation

We report a novel form of xylem dysfunction in angiosperms: reversible collapse of the xylem conduits of the smallest vein orders that demarcate and intrusively irrigate the areoles of red oak (Quercus rubra) leaves. Cryo-scanning electron microscopy revealed gradual increases in collapse from approximately -2 MPa down to -3 MPa, saturating thereafter (to -4 MPa). Over this range, cavitation remained negligible in these veins. Imaging of rehydration experiments showed spatially variable recovery from collapse within 20 s and complete recovery after 2 min. More broadly, the patterns of deformation induced by desiccation in both mesophyll and xylem suggest that cell wall collapse is unlikely to depend solely on individual wall properties, as mechanical constraints imposed by neighbors appear to be important. From the perspective of equilibrium leaf water potentials, petioles, whose vessels extend into the major veins, showed a vulnerability to cavitation that overlapped in the water potential domain with both minor vein collapse and buckling (turgor loss) of the living cells. However, models of transpiration transients showed that minor vein collapse and mesophyll capacitance could effectively buffer major veins from cavitation over time scales relevant to the rectification of stomatal wrong-way responses. We suggest that, for angiosperms, whose subsidiary cells give up large volumes to allow large stomatal apertures at the cost of potentially large wrong-way responses, vein collapse could make an important contribution to these plants' ability to transpire near the brink of cavitation-inducing water potentials.

Effects of Osmolality on Paracellular Transport in MDCK II Cells

Epithelia separate apical and basal compartments, and movement of substances via the paracellular pathway is regulated by tight junctions. Claudins are major constituents of tight junctions and involved in the regulation of tight junction permeability. On the other hand, the osmolality in the extracellular environment fluctuates in association with life activity. However, effects of osmotic changes on the permeaibility of claudins are poorly understood. Therefore, we investigated the effects of osmotic changes on the paracellular transport in MDCK II cells. Interestingly, apical hyposmolality decreased cation selectivity in the paracellular pathway gradually with time, and the elimination of the osmotic gradient promptly restored the cation selectivity. Apical hyposmolality also induced bleb formation at cell-cell contacts and changed the shape of cell-cell contacts from a jagged pattern to a slightly linear pattern. In claudin-2 knockout MDCK II cells, the decrease of cation selectivity, the bleb formation, nor the changes in the shape of cell-cell contacts was observed under the apical hyposmolality. Our findings in this study indicate that osmotic gradient between apical and basal sides is involved in the acute regulation of the cation selective property of claudin-2 channels.

Studying the Supramolecular Organization of Photosynthetic Membranes within Freeze-fractured Leaf Tissues by Cryo-scanning Electron Microscopy

Cryo-scanning electron microscopy (SEM) of freeze-fractured samples allows investigation of biological structures at near native conditions. Here, we describe a technique for studying the supramolecular organization of photosynthetic (thylakoid) membranes within leaf samples. This is achieved by high-pressure freezing of leaf tissues, freeze-fracturing, double-layer coating and finally cryo-SEM imaging. Use of the double-layer coating method allows acquiring high magnification (>100,000X) images with minimal beam damage to the frozen-hydrated samples as well as minimal charging effects. Using the described procedures we investigated the alterations in supramolecular distribution of photosystem and light-harvesting antenna protein complexes that take place during dehydration of the resurrection plant Craterostigma pumilum, in situ.

The plasma membrane and matrix vesicles of mouse growth plate chondrocytes during differentiation as revealed in freeze-fracture replicas

The epiphyseal cartilage in mouse tibia and fibula was investigated with the freeze-fracture method. Cytodifferentiation of growth plate chondrocytes was found to be marked by changes in both cell membrane and extracellular matrix vesicle membranes. Exocytosis and endocytosis were observed in all zones of differentiation, with endocytosis being predominant in the reserve and proliferative zones and exocytosis occurring with greatest frequency during hypertrophy. Intramembraneous particles (IMPs) on the plasma membrane were distributed evenly on the reserve and proliferative cell membranes, whereas in the hypertrophic zone IMPs tended to be distributed asymmetrically. Several types of matrix vesicles were identifiable on the basis of IMP distribution: IMP-free, IMP-aggregated, and IMP-random. The distribution pattern of IMPs on vesicles varied with differentiation of the chondrocytes. For proliferative and prehypertrophic cells, most matrix vesicles belonged to the IMP-random category. IMP-aggregated and IMP-free matrix vesicles became increasingly frequent in the later stages of differentiation, particularly in the late hypertrophic stage. IMPs were observed more frequently on the convex protoplasmic fracture face of matrix vesicles than on the concave exoplasmic fracture face, as was also observed for the plasma membrane. Matrix vesicles formation appears to occur by budding from chondrocyte projections and bulges at the smooth surfaces of the cells and from cell disintegration. Crystals of mineral were apparent in cross-fractured matrix vesicles of the calcifying zone, but not in the other zones.

Ultrastructural characterization of epithelial cell membranes in normal human conducting airway epithelium: A freeze-fracture study

Cell membranes of normal human nasal and tracheal epithelium were characterized by means of freeze-fracture preparations. These investigations illustrated a predictable variability in the distribution of membrane-associated particles on PF-faces of different cell types and in different regions of the same cell. Details of the fine structure and variability of tight junctional complexes in different cell types are presented as are ultrastructural perspectives of cell membrane involvement in ciliogenesis and in mucus secretion. Because ciliogenic profiles and nascent tight junctional complexes were observed more frequently in nasal epithelial cells, these features provided markers of cellular differentiation. Based on the frequent appearance of such indicators, these observations suggested that cell turnover may be more rapid in the region of the nasal turbinates than in the trachea. There was no appreciable evidence of ultrastructural variability between the epithelial cell membranes of similar cell types in the upper and lower respiratory tract.

Detection of anionic sites on the cytoplasmic surface of the guinea pig acrosomal membrane

The sperm acrosome reaction is an example of exocytosis, accomplished through the fusion of the acrosomal and plasma membranes. As in other examples of exocytosis, the acrosome reaction is initiated by an influx of Ca++, which may promote fusion by binding to anionic sites on adjacent bilayers. In this study we used ruthenium red (RR) and cationic ferritin (CF) to detect anionic sites on the surfaces of acrosomal and plasma membranes of guinea pig spermatozoa. These probes indicate a dense concentration of anionic sites on the cytoplasmic surface of the acrosomal membrane. Higher concentrations of salt (NaCl) were required to inhibit cationic probe labeling of the cytoplasmic surface of the acrosomal membrane compared to the concentration needed to inhibit the plasma membrane binding. The added NaCl also increased the separation of the plasma from the acrosomal membrane. Low-pH buffers stop cationic probe labeling of both membranes. Sections tangential to the acrosomal membrane revealed that the cation probes bound in a linear pattern, similar to the periodicity and distribution of intramembraneous particles observed in freeze-fracture replicas. Following fusion of the plasma and acrosomal membrane during the acrosome reaction, we could no longer detect a dense concentration of anionic sites on the cytoplasmic surface of the fused vesicles. The results indicate that the dense concentrations of anionic sites are either masked or lost following fusion with the overlying plasma membrane.

Recapitulating cranial osteogenesis with neural crest cells in 3-D microenvironments

The experimental systems that recapitulate the complexity of native tissues and enable precise control over the microenvironment are becoming essential for the pre-clinical tests of therapeutics and tissue engineering. Here, we described a strategy to develop an in vitro platform to study the developmental biology of craniofacial osteogenesis. In this study, we directly osteo-differentiated cranial neural crest cells (CNCCs) in a 3-D in vitro bioengineered microenvironment. Cells were encapsulated in the gelatin-based photo-crosslinkable hydrogel and cultured up to three weeks. We demonstrated that this platform allows efficient differentiation of p75 positive CNCCs to cells expressing osteogenic markers corresponding to the sequential developmental phases of intramembranous ossification. During the course of culture, we observed a decrease in the expression of early osteogenic marker Runx2, while the other mature osteoblast and osteocyte markers such as Osterix, Osteocalcin, Osteopontin and Bone sialoprotein increased. We analyzed the ossification of the secreted matrix with alkaline phosphatase and quantified the newly secreted hydroxyapatite. The Field Emission Scanning Electron Microscope (FESEM) images of the bioengineered hydrogel constructs revealed the native-like osteocytes, mature osteoblasts, and cranial bone tissue morphologies with canaliculus-like intercellular connections. This platform provides a broadly applicable model system to potentially study diseases involving primarily embryonic craniofacial bone disorders, where direct diagnosis and adequate animal disease models are limited.

Effects of ursolic acid on the structural and morphological behaviours of dipalmitoyl lecithin vesicles

Effects of ursolic acid on the structural and morphological characteristics of dipalmitoyl lecithin(DPPC)-water system was studied by using differential scanning calorimetry (DSC), small- and wide-angle X-ray scattering (SWAXS), freeze-fracture method combined with transmission electron-microscopy (FF-TEM) and infrared spectroscopy (FT-IR). The surface of the uncorrelated lipid system is rippled or grained and a huge number of small, presumably unilamellar vesicles are present if the UA/DPPC molar ratio is 0.1 mol/mol or higher. Besides the destroyed layer packing of regular multilamellar vesicles, non-bilayer (e.g. cubic or hexagonal) local structures are evidenced by SAXS and FF-TEM methods. The ability of UA to induce non-bilayer structures in hydrated DPPC system originates from the actual geometry form of associated lipid and UA molecules as concluded from the FT-IR measurements and theoretical calculations. Beside numerous beneficial e.g. chemopreventive and chemotherapeutic effect of ursolic acid against cancer, their impact to modify the lipid bilayers can be utilized in liposomal formulations.

The fine structure of the glomeruli as revealed by freeze-fracturing

Isolated glomeruli of the rat kidney were investigated using the freeze-fracture method. The observations were consistent with those made on thin sections. Only exceptionally components of zonulae occludentes were seen between the capillary endothelial cells. The split membrane of mesangial cells revealed aspects of gap junctions.

Kearns-Sayre syndrome: primarily a mitochondriopathy?

Histopathological changes of the external eye muscles and of the peripheral skeletal muscles of 2 patients with Kearns-Sayre syndrome are demonstrated histochemically and electron microscopically. In one case the progression of the mitochondrial anomalies in this disease was documented through ultrastructural investigations of muscle biopsies over a period of 17 years. By freeze-fracture the membrane fracture faces of the transformed mitochondrial were examined in both patients. Biochemical results of one patient show that energy production by glycolysis is distinctly decreased with respect to oxydation. Clinical, morphological and biochemical results support the hypothesis that the Kearns-Sayre syndrome is caused by a primary mitochondriopathy which is not limited to the musculature.

Interfacial and emulsifying properties of soybean peptides with different degrees of hydrolysis

In this study, the effects of the degree of hydrolysis on the interfacial and emulsifying properties of soybean peptides were evaluated based on surface and interfacial tension, dynamic light scattering (DLS), and freeze-fracture transmission electron microscopy (FF-TEM) analyses. Of the five evaluated soybean peptides (SP95, SP87, SP75, SP49, and SP23), those with higher degrees of hydrolysis (SP95 and SP87) did not exhibit noticeable surface-active properties in water, whereas those with relatively low degrees of hydrolysis (SP75, SP49, and SP23) exhibited remarkable surface tension-lowering activity. The latter set (SP75, SP49, and SP23) also formed giant associates with average sizes ranging from 64.5 nm to 82.6 nm above their critical association concentration (CAC). Moreover, SP23 with the lowest degree of hydrolysis exhibited excellent emulsifying activity for soybean oil, and FF-TEM analysis demonstrated that the emulsions were stabilized by a lamella-like multilayer peptide structure on the oil droplets that prevented coagulation. The peptide with the lowest degree of hydrolysis (SP23) was effective not only for soybean oil emulsification, but also for the emulsification of liquid paraffin and silicon oil that are generally difficult to emulsify.

Characterization of freeze-fractured epithelial plasma membranes on nanometer scale with ToF-SIMS

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to characterize the freeze-fracturing process of human epithelial PANC-1 and UROtsa cells. For this purpose, phosphatidylcholine, sphingomyelin, phosphatidylethanolamine, and phosphatidylserine standard samples were investigated to find specific signals with both high specificity and signal intensity. The results were used to investigate single cells of subconfluent cell layers prepared with a special silicon wafer sandwich preparation technique. This freeze-fracturing technique strips cell membranes off the cells, isolating them on opposing silicon wafer substrates. Criteria were found for defining regions with stripped off cell membranes and, on the opposing wafer, complementary regions with the remaining cells. Measured ethanolamine/choline and serine/choline ratios in these regions clearly showed that in the freeze-fracturing process, the lipid bilayer of the plasma membrane is split along its central zone. Accordingly, only the outer lipid monolayer is stripped off the cell, while the inner lipid monolayer remains attached to the cell on the opposing wafer, thus allowing detailed analysis of a single lipid monolayer. Furthermore, it could be shown that using different washing procedures did not influence the transmembrane lipid distribution. Under optimized preparation conditions, it became feasible to detect lipids with a lateral resolution of approximately 100 nm. The data indicate that ToF-SIMS would be a very useful technique to study with very high lateral resolution changes in lipid composition caused, for example, by lipid storage diseases or pharmaceuticals that interfere with the lipid metabolism.

Sequestration Revisited: Integrating Traditional Electron Microscopy, De Novo Assembly and New Results

Electron microscopy analysis of the autophagic sequestration membrane (SM) in various metazoan cell types after different fixation methods shows that: (1) the growing SM cannot derive from preformed rough surfaced endoplasmic reticulum (RER) membranes by transformation; (2) the empty cleft between the two layers of the SM after aldehyde fixation is an artifact of sample preparation; (3) the SM emerges from and grows de novo in cytoplasmic areas where membranous precursors cannot be identified by traditional electron microscopy; (4) the growing SM consists of two tightly packed membrane layers with a sharp bend at the edge; (5) changes in the environment of the growing SM participate in the determination of the size and shape of the autophagosome. We suggest that expansion as well as regression takes place at the edge of the growing SM. Stabilization and irreversibility of formation of the SM is achieved by closure. The immediate source of lipids for the SM must be in the cytoplasmic matrix, supposedly in the form of special phospholipid carrying vesicles that might involve the transmembrane Atg9 protein. To explain the apparent lack of such vesicles by electron microscopy we suggest that they are too small, have a similar density to other frequently occurring structures, or are destroyed during sample preparation.

Regional changes of AQP0-dependent square array junction and gap junction associated with cortical cataract formation in the Emory mutant mouse

The Emory mutant mouse has been widely used as an animal model for human senile cataract since it develops late-onset hereditary cataract. Here, we focus on the regional changes of aquaporin-0 (AQP0) and connexins that are associated with the cortical cataract formation in the Emory mutant mice. Emory mutant and CFW wild-type mice at age 1-16 months were used in this study. By using an established photography system with dissecting microscopy, the opacities were first detected at the anterior or posterior lens center surface in Emory mice at age 7 months, and gradually extended toward the equator during the 16 months examined. Scanning EM verified that disorganized and fragmented fiber cells were associated with the areas of opacities within approximately 200 μm from the lens surface, indicating that Emory mouse cataracts belong to the cortical cataracts. Freeze-fracture TEM further confirmed that cortical cataracts exhibited extensive wavy square array junctions, small gap junctions and globules. Immunofluorescence analysis showed that in contrast to the high labeling intensity of AQP0-loop antibody, the labeling of AQP0 C-terminus antibody was decreased considerably in superficial fibers in Emory cataracts. Similarly, a significant decrease in the labeling of the antibody against Cx50 C-terminus, but not Cx46 C-terminus, occurred in superficial and outer cortical fibers in Emory cataracts. Western blotting further revealed that the C-termini of both AQP0 and Cx50 in Emory cataracts were decreased to over 50% to that of the wild-type. Thus, this systematic study concludes that the Emory mouse cataract belongs to the cortical cataract which is due to regional breakdown of superficial fibers associated with formation of AQP0-dependent wavy square array junctions, small gap junctions and globules. The marked decreases of the C-termini of both AQP0 and Cx50 in the superficial fibers may disturb the needed interaction between these two proteins during fiber cell differentiation and thus play a role in the cortical cataract formation in Emory mutant mice.

Development of a new resistant liposome coated with polysaccharide film for cosmetic application

The aim of our study was to elaborate a resistant liposome that can be used in cosmetic formulations containing high amounts of surfactants and electrolytes. The stability of liposomes was increased via hydrophobized polysaccharide (Stearoyl Inulin) by anchoring its stearic acid tail into liposome bilayer. Coated and noncoated liposomes were prepared under the same conditions and their morphology, size, and resistance to surfactants and electrolytes were evaluated. We established that coated lipbsomes were more resistant to surfactants and electrolytes. It seems that a coating of polysaccharides prevents liposome destabilization in the presence of high amounts of surfactants and electrolytes. Moreover, the ability of coated liposomes to improve the skin delivery of active molecules was evaluated. Coated liposomes increased the efficacy of magnesium chloride by improving its skin availability.

Membrane-active mechanism of LFchimera against Burkholderia pseudomallei and Burkholderia thailandensis

LFchimera, a construct combining two antimicrobial domains of bovine lactoferrin, lactoferrampin265-284 and lactoferricin17-30, possesses strong bactericidal activity. As yet, no experimental evidence was presented to evaluate the mechanisms of LFchimera against Burkholderia isolates. In this study we analyzed the killing activity of LFchimera on the category B pathogen Burkholderia pseudomallei in comparison to the lesser virulent Burkholderia thailandensis often used as a model for the highly virulent B. pseudomallei. Killing kinetics showed that B. thailandensis E264 was more susceptible for LFchimera than B. pseudomallei 1026b. Interestingly the bactericidal activity of LFchimera appeared highly pH dependent; B. thailandensis killing was completely abolished at and below pH 6.4. FITC-labeled LFchimera caused a rapid accumulation within 15 min in the cytoplasm of both bacterial species. Moreover, freeze-fracture electron microscopy demonstrated extreme effects on the membrane morphology of both bacterial species within 1 h of incubation, accompanied by altered membrane permeability monitored as leakage of nucleotides. These data indicate that the mechanism of action of LFchimera is similar for both species and encompasses disruption of the plasma membrane and subsequently leakage of intracellular nucleotides leading to cell dead.

Molecular modeling and imaging of initial stages of cellulose fibril assembly: evidence for a disordered intermediate stage

The remarkable mechanical strength of cellulose reflects the arrangement of multiple β-1,4-linked glucan chains in a para-crystalline fibril. During plant cellulose biosynthesis, a multimeric cellulose synthesis complex (CSC) moves within the plane of the plasma membrane as many glucan chains are synthesized from the same end and in close proximity. Many questions remain about the mechanism of cellulose fibril assembly, for example must multiple catalytic subunits within one CSC polymerize cellulose at the same rate? How does the cellulose fibril bend to align horizontally with the cell wall? Here we used mathematical modeling to investigate the interactions between glucan chains immediately after extrusion on the plasma membrane surface. Molecular dynamics simulations on groups of six glucans, each originating from a position approximating its extrusion site, revealed initial formation of an uncrystallized aggregate of chains from which a protofibril arose spontaneously through a ratchet mechanism involving hydrogen bonds and van der Waals interactions between glucose monomers. Consistent with the predictions from the model, freeze-fracture transmission electron microscopy using improved methods revealed a hemispherical accumulation of material at points of origination of apparent cellulose fibrils on the external surface of the plasma membrane where rosette-type CSCs were also observed. Together the data support the possibility that a zone of uncrystallized chains on the plasma membrane surface buffers the predicted variable rates of cellulose polymerization from multiple catalytic subunits within the CSC and acts as a flexible hinge allowing the horizontal alignment of the crystalline cellulose fibrils relative to the cell wall.

Claudin-3 and claudin-5 protein folding and assembly into the tight junction are controlled by non-conserved residues in the transmembrane 3 (TM3) and extracellular loop 2 (ECL2) segments

The mechanism of tight junction (TJ) assembly and the structure of claudins (Cldn) that form the TJ strands are unclear. This limits the molecular understanding of paracellular barriers and strategies for drug delivery across tissue barriers. Cldn3 and Cldn5 are both common in the blood-brain barrier but form TJ strands with different ultrastructures. To identify the molecular determinants of folding and assembly of these classic claudins, Cldn3/Cldn5 chimeric mutants were generated and analyzed by cellular reconstitution of TJ strands, live cell confocal imaging, and freeze-fracture electron microscopy. A comprehensive screening was performed on the basis of the rescue of mutants deficient for strand formation. Cldn3/Cldn5 residues in transmembrane segment 3, TM3 (Ala-127/Cys-128, Ser-136/Cys-137, Ser-138/Phe-139), and the transition of TM3 to extracellular loop 2, ECL2 (Thr-141/Ile-142) and ECL2 (Asn-148/Asp-149, Leu-150/Thr-151, Arg-157/Tyr-158), were identified to be involved in claudin folding and/or assembly. Blue native PAGE and FRET assays revealed 1% n-dodecyl β-d-maltoside-resistant cis-dimerization for Cldn5 but not for Cldn3. This homophilic interaction was found to be stabilized by residues in TM3. The resulting subtype-specific cis-dimer is suggested to be a subunit of polymeric TJ strands and contributes to the specific ultrastructure of the TJ detected by freeze-fracture electron microscopy. In particular, the Cldn5-like exoplasmic face-associated and particle-type strands were found to be related to cis-dimerization. These results provide new insight into the mechanisms of paracellular barrier formation by demonstrating that defined non-conserved residues in TM3 and ECL2 of classic claudins contribute to the formation of TJ strands with differing ultrastructures.

Connexin36 in gap junctions forming electrical synapses between motoneurons in sexually dimorphic motor nuclei in spinal cord of rat and mouse

Pools of motoneurons in the lumbar spinal cord innervate the sexually dimorphic perineal musculature, and are themselves sexually dimorphic, showing differences in number and size between male and female rodents. In two of these pools, the dorsomedial nucleus (DMN) and the dorsolateral nucleus (DLN), dimorphic motoneurons are intermixed with non-dimorphic neurons innervating anal and external urethral sphincter muscles. As motoneurons in these nuclei are reportedly linked by gap junctions, we examined immunofluorescence labeling for the gap junction-forming protein connexin36 (Cx36) in male and female mice and rats. Fluorescent Cx36-labeled puncta occurred in distinctly greater amounts in the DMN and DLN of male rodents than in other spinal cord regions. These puncta were localized to motoneuron somata, proximal dendrites, and neuronal appositions, and were distributed either as isolated or large patches of puncta. In both rats and mice, Cx36-labeled puncta were associated with nearly all (> 94%) DMN and DLN motoneurons. The density of Cx36-labeled puncta increased dramatically from postnatal days 9 to 15, unlike the developmental decreases in these puncta observed in other central nervous system regions. In females, Cx36 labeling of puncta in the DLN was similar to that in males, but was sparse in the DMN. In enhanced green fluorescent protein (EGFP)-Cx36 transgenic mice, motoneurons in the DMN and DLN were intensely labeled for the EGFP reporter in males, but less so in females. The results indicate the presence of Cx36-containing gap junctions in the sexually dimorphic DMN and DLN of both male and female rodents, suggesting coupling of not only sexually dimorphic but also non-dimorphic motoneurons in these nuclei.

Isolation and characterization of the ejectisomes of the prasinophyte Pyramimonas grossii

For the first time, ejectisome-enriched fractions were isolated from the marine prasinophyte Pyramimonas grossii. Transmission electron microscopy revealed that most of the ejectisomes were discharged and formed long, spirally twisted filaments. Some ejectisomes were still fully or partly furled. Discharged ejectisomes measured up to 26 μm in length and 200 nm in width; those still furled measured up to 900 nm in width and 1,000 nm in length. Particle periodicities of approximately 4.2 and 5.8 nm could be measured from freeze-fractured filaments. Sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed a protein banding pattern, dominated by polypeptides of 16-20 kDa. These polypeptides were not glycosylated and did not cross-react with antisera directed against recombinant R-body polypeptides of Caedibacter taeniospiralis or directed against reconstituted cryptophycean ejectisomes.

The stack: a new bacterial structure analyzed in the Antarctic bacterium Pseudomonas deceptionensis M1(T) by transmission electron microscopy and tomography

In recent years, improvements in transmission electron microscopy (TEM) techniques and the use of tomography have provided a more accurate view of the complexity of the ultrastructure of prokaryotic cells. Cryoimmobilization of specimens by rapid cooling followed by freeze substitution (FS) and sectioning, freeze fracture (FF) and observation of replica, or cryoelectron microscopy of vitreous sections (CEMOVIS) now allow visualization of biological samples close to their native state, enabling us to refine our knowledge of already known bacterial structures and to discover new ones.

Application of these techniques to the new Antarctic cold-adapted bacterium Pseudomonasdeceptionensis M1^T has demonstrated the existence of a previously undescribed cytoplasmic structure that does not correspond to known bacterial inclusion bodies or membranous formations. This structure, which we term a “stack”, was mainly visualized in slow growing cultures of P. deceptionensis M1^T and can be described as a set of stacked membranous discs usually arranged perpendicularly to the cell membrane, but not continuous with it, and found in variable number in different locations within the cell. Regardless of their position, stacks were mostly observed very close to DNA fibers. Stacks are not exclusive to P. deceptionensis M1^T and were also visualized in slow-growing cultures of other bacteria. This new structure deserves further study using cryoelectron tomography to refine its configuration and to establish whether its function could be related to chromosome dynamics.

Flash thermal conditioning of olive pastes during the olive oil mechanical extraction process: impact on the structural modifications of pastes and oil quality

The quality of virgin olive oil (VOO) is strictly related to the concentrations of phenolic and volatile compounds, which are strongly affected by the operative conditions of the VOO mechanical extraction process. The aim of this work is to study the impact of a new technology such as flash thermal conditioning (FTC) on olive paste structural modification and on VOO quality. The evaluation of olive paste structure modification by cryo-scanning electron microscopy (cryo-SEM) showed that the application of FTC after crushing produces significant differences in terms of the breaking of the parenchyma cells and aggregation of oil droplets in comparison to the crushed pastes. The virgin olive oil flash thermal conditioning (VOO-FTC) featured a higher concentration of volatile compounds compared to that in the control, particularly of all saturated and unsaturated aldehydes and esters, whereas the phenolic concentration was higher in VOO obtained from the traditional process (VOO-C).

The mechanism of toxicity in HET-S/HET-s prion incompatibility

The HET-s protein from the filamentous fungus Podospora anserina is a prion involved in a cell death reaction termed heterokaryon incompatibility. This reaction is observed at the point of contact between two genetically distinct strains when one harbors a HET-s prion (in the form of amyloid aggregates) and the other expresses a soluble HET-S protein (96% identical to HET-s). How the HET-s prion interaction with HET-S brings about cell death remains unknown; however, it was recently shown that this interaction leads to a relocalization of HET-S from the cytoplasm to the cell periphery and that this change is associated with cell death. Here, we present detailed insights into this mechanism in which a non-toxic HET-s prion converts a soluble HET-S protein into an integral membrane protein that destabilizes membranes. We observed liposomal membrane defects of approximately 10 up to 60 nm in size in transmission electron microscopy images of freeze-fractured proteoliposomes that were formed in mixtures of HET-S and HET-s amyloids. In liposome leakage assays, HET-S has an innate ability to associate with and disrupt lipid membranes and that this activity is greatly enhanced when HET-S is exposed to HET-s amyloids. Solid-state nuclear magnetic resonance (NMR) analyses revealed that HET-s induces the prion-forming domain of HET-S to adopt the β-solenoid fold (previously observed in HET-s) and this change disrupts the globular HeLo domain. These data indicate that upon interaction with a HET-s prion, the HET-S HeLo domain partially unfolds, thereby exposing a previously buried ∼34-residue N-terminal transmembrane segment. The liberation of this segment targets HET-S to the membrane where it further oligomerizes, leading to a loss of membrane integrity. HET-S thus appears to display features that are reminiscent of pore-forming toxins.

Kv4.2 potassium channels segregate to extrasynaptic domains and influence intrasynaptic NMDA receptor NR2B subunit expression

Neurons of the intercalated cell clusters (ITCs) represent an important relay site for information flow within amygdala nuclei. These neurons receive mainly glutamatergic inputs from the basolateral amygdala at their dendritic domains and provide feed-forward inhibition to the central nucleus. Voltage-gated potassium channels type-4.2 (Kv4.2) are main players in dendritic signal processing and integration providing a key component of the A currents. In this study, the subcellular localization and distribution of the Kv4.2 was studied in ITC neurons by means of light- and electron microscopy, and compared to other types of central principal neurons. Several ultrastructural immunolocalization techniques were applied including pre-embedding techniques and, most importantly, SDS-digested freeze-fracture replica labeling. We found Kv4.2 densely expressed in somato-dendritic domains of ITC neurons where they show a differential distribution pattern as revealed by nearest neighbor analysis. Comparing ITC neurons with hippocampal pyramidal and cerebellar granule cells, a cell type- and domain-dependent organization in Kv4.2 distribution was observed. Kv4.2 subunits were localized to extrasynaptic sites where they were found to influence intrasynaptic NMDA receptor subunit expression. In samples of Kv4.2 knockout mice, the frequency of NR1-positive synapses containing the NR2B subunit was significantly increased. This indicates a strong, yet indirect effect of Kv4.2 on the synaptic content of NMDA receptor subtypes, and a likely role in synaptic plasticity at ITC neurons.

Mechanism of gelation in the hydrogenated soybean lecithin (PC70)/hexadecanol/water system

The crude phospholipid mixture (PC70) forms a homogeneous gel with hexadecanol (HD) in water, whereas the purified lipid does not. The fact that the crude material PC70 can be utilized for homogeneous gel preparation suits the cosmetic industry very well from the viewpoint of cost performance. In order to clarify the mechanism of the gelation, we investigated the structures and physicochemical properties of the PC70/HD/water system by rheometry, freeze-fracture electron microscopy, differential scanning calorimetry (DSC) and synchrotron X-ray diffraction. Our results suggested that the gelation is induced by change in bilayer morphology from closed vesicles to sheet-like structures with open edges covered by minor lipid components that are stiffened due to intercalation of HD molecules between phospholipids. The morphological change may give rise to homogeneous distribution of the bilayer sheets throughout the solution and formation of water continuum that may work as a network in the gel.

Electron tomography of fusiform vesicles and their organization in urothelial cells

The formation of fusiform vesicles (FVs) is one of the most distinctive features in the urothelium of the urinary bladder. FVs represent compartments for intracellular transport of urothelial plaques, which modulate the surface area of the superficial urothelial (umbrella) cells during the distension-contraction cycle. We have analysed the three-dimensional (3D) structure of FVs and their organization in umbrella cells of mouse urinary bladders. Compared to chemical fixation, high pressure freezing gave a new insight into the ultrastructure of urothelial cells. Electron tomography on serial sections revealed that mature FVs had a shape of flattened discs, with a diameter of up to 1.2 µm. The lumen between the two opposing asymmetrically thickened membranes was very narrow, ranging from 5 nm to 10 nm. Freeze-fracturing and immunolabelling confirmed that FVs contain two opposing urothelial plaques connected by a hinge region that made an omega shaped curvature. In the central cytoplasm, 4-15 FVs were often organized into stacks. In the subapical cytoplasm, FVs were mainly organized as individual vesicles. Distension-contraction cycles did not affect the shape of mature FVs; however, their orientation changed from parallel in distended to perpendicular in contracted bladder with respect to the apical plasma membrane. In the intermediate cells, shorter and more dilated immature FVs were present. The salient outcome from this research is the first comprehensive, high resolution 3D view of the ultrastructure of FVs and how they are organized differently depending on their location in the cytoplasm of umbrella cells. The shape of mature FVs and their organization into tightly packed stacks makes them a perfect storage compartment, which transports large amounts of urothelial plaques while occupying a small volume of umbrella cell cytoplasm.

Trafficking of gap junction channels at a vertebrate electrical synapse in vivo

Trafficking and turnover of transmitter receptors required to maintain and modify the strength of chemical synapses have been characterized extensively. In contrast, little is known regarding trafficking of gap junction components at electrical synapses. By combining ultrastructural and in vivo physiological analysis at identified mixed (electrical and chemical) synapses on the goldfish Mauthner cell, we show here that gap junction hemichannels are added at the edges of GJ plaques where they dock with hemichannels in the apposed membrane to form cell-cell channels and, simultaneously, that intact junctional regions are removed from centers of these plaques into either presynaptic axon or postsynaptic dendrite. Moreover, electrical coupling is readily modified by intradendritic application of peptides that interfere with endocytosis or exocytosis, suggesting that the strength of electrical synapses at these terminals is sustained, at least in part, by fast (in minutes) turnover of gap junction channels. A peptide corresponding to a region of the carboxy terminus that is conserved in Cx36 and its two teleost homologs appears to interfere with formation of new gap junction channels, presumably by reducing insertion of hemichannels on the dendritic side. Thus, our data indicate that electrical synapses are dynamic structures and that their channels are turned over actively, suggesting that regulated trafficking of connexons may contribute to the modification of gap junctional conductance.

Polymorphism of natural fatty acid liquid crystalline phases

We study the phase behavior in water of a mixture of natural long chain fatty acids (FAM) in association with ethylenediamine (EDA) and report a rich polymorphism depending on the composition. At a fixed EDA/FAM molar ratio, we observe upon dilution a succession of organized phases going from a lamellar phase to a hexagonal phase and, finally, to cylindrical micelles. The phase structure is established using polarizing microscopy, SAXS, and SANS. Interestingly, in the lamellar phase domain, we observe the presence of defects upon dilution, which SAXS shows to correspond to intrabilayer correlations. NMR and FF-TEM techniques suggest that these defects are related to an increase in the spontaneous curvature of the molecule monolayers in the lamellae. ATR-FTIR spectroscopy was also used to investigate the degree of ionization within these assemblies. The successive morphological transitions are discussed with regards to possible molecular mechanisms, in which the interaction between the acid surfactant and the amine counterion plays the leading role.

Macrophages sequester clofazimine in an intracellular liquid crystal-like supramolecular organization

Clofazimine is a poorly-soluble but orally-bioavailable small molecule drug that massively accumulates in macrophages when administered over prolonged periods of time. To determine whether crystal-like drug inclusions (CLDIs) that form in subcellular spaces correspond to pure clofazimine crystals, macrophages of clofazimine-fed mice were elicited with an intraperitoneal thioglycollate injection. Inside these cells, CLDIs appeared uniform in size and shape, but were sensitive to illumination. Once removed from cells, CLDIs were unstable. Unlike pure clofazimine crystals, isolated CLDIs placed in distilled water burst into small birefringent globules, which aggregated into larger clusters. Also unlike pure clofazimine crystals, CLDIs fragmented when heated, and disintegrated in alkaline media. In contrast to all other organelles, CLDIs were relatively resistant to sonication and trypsin digestion, which facilitated their biochemical isolation. The powder x-ray diffraction pattern obtained from isolated CLDIs was consistent with the diffraction pattern of liquid crystals and inconsistent with the expected molecular diffraction pattern of solid, three dimensional crystals. Observed with the transmission electron microscope (TEM), CLDIs were bounded by an atypical double-layered membrane, approximately 20 nanometers thick. CLDIs were polymorphic, but generally exhibited an internal multilayered organization, comprised of stacks of membranes 5 to 15 nanometers thick. Deep-etch, freeze-fracture electron microscopy of unfixed snap-frozen tissue samples confirmed this supramolecular organization. These results suggest that clofazimine accumulates in macrophages by forming a membrane-bound, multilayered, liquid crystal-like, semi-synthetic cytoplasmic structure.

Comparative studies on the crystalline to fluid phase transitions of two equimolar cationic/anionic surfactant mixtures containing dodecylsulfonate and dodecylsulfate

In this work, a cationic surfactant, dodecyltrimethylammonium bromide (DTAB), and an anionic surfactant, sodium dodecylsulfonate (SDSO(3)) or sodium dodecylsulfate (SDSO(4)), were mixed in an equimolar ratio to prepare SDSO(3)-DTAB and SDSO(4)-DTAB binary mixtures. The phase behavior, structure, and morphology of these two surfactant mixtures were investigated by differential scanning calorimetry, synchrotron X-ray scattering, freeze-fracture electron microscopy, and Fourier transform infrared spectroscopy. It was found that upon heating, both of the two systems transform from multilamellar crystalline phase to liquid crystalline (or fluid) phase. It is interesting to find that, although SDSO(3) has a lower molecular weight, the crystalline phase of SDSO(3)-DTAB shows much higher thermostability as compared with that of SDSO(4)-DTAB. Other than this, we observed a large difference in the repeat distances of the two crystalline phases. More interestingly, at 60 °C in the fluid phases, cylindrical micelles formed in the SDSO(3)-DTAB system, while spherical micelles were observed in the SDSO(4)-DTAB system. Our present work demonstrates that a subtle difference in the headgroup structure of the anionic component markedly affects the thermostability, packing structure, and morphology of the surfactant mixtures, which suggests the importance of the match of the head-head and tail-tail interactions between the cationic and anionic surfactants.

Does lactobionic acid affect the colloidal structure and skin moisturizing potential of the alkyl polyglucoside-based emulsion systems?

Moisturizing creams are the most prescribed products in dermatology, essential in maintaining healthy skin as well as in the topical treatment of some diseases. The irritation potential of commonly used emulsifiers and moisturizing ingredients, but also their mutual interactions, could affect the functionality and safety of those dermopharmaceutics. The aim of this study was to promote moisturizing alkyl polyglucoside (APG)-based emulsion as vehicle for lactobionic acid (LA), advantageous representative of the alphahydroxyacids (AHAs)-multifunctional moisturizers, assessing the safety for use (in vitro acute skin irritation test using cytotoxicity assay compared with in vivo data obtained using skin bioengineering methods) and in vivo moisturizing capacity (bioengineering of the skin). In order to investigate possible interactions between APG mild natural emulsifier-based emulsion and LA, a deeper insight into the colloidal structure of the placebo and the emulsion with LA was given using polarization and transmission electron microscopy, rheology, thermal and texture analysis. This study showed that APG-based emulsions could be promoted as safe cosmetic/dermopharmaceutical vehicles and carriers for extremely acidic and hygroscopic AHA class of actives (specifically LA); prospective safety for human use of both APG and LA with the correlation between in vivo and in vitro findings was shown. However, it was revealed that LA strongly influenced the colloidal structure of the emulsion based on APGs and promoted the formation of lamellar structures which reflects onto the mode of water distribution within the cream. The advantageous skin hydrating potential of LA-containing emulsion vs. placebo was unlikely to be achieved, pointing that emulsions stabilized by lamellar liquid crystalline structures probably are not satisfying carriers for highly hygroscopic actives in order to reach the full moisturizing potential. Safe and effective use on dry skin is presumed.

A comparative study of the thermal and dynamic mechanical behaviour of quenched and annealed bioresorbable poly-L-lactide/α-tricalcium phosphate nanocomposites

Despite numerous reports on the degradation properties and biological efficacy of bioresorbable polymer nanocomposites intended for use in orthopaedics, there is currently limited literature addressing their thermal and load-bearing properties, which are of central importance to the successful design of these nanocomposites. Here we demonstrate that the storage moduli at 37°C and the glass transition temperatures of quenched poly-L-lactide/α-tricalcium phosphate nanocomposites were lower than those of annealed nanocomposites while the damping factor tanδ values of the quenched nanocomposites were higher than those of the annealed nanocomposites. This was due to the highly crystalline structure of the annealed samples, as confirmed by wide angle X-ray diffraction. The higher storage moduli and glass transition temperatures of the annealed nanocomposites implies that higher energy will be generated to resist deformation with the possibility for reduced polymer chain mobility during in vivo use. Therefore, the decision as to whether to use quenched or annealed nanocomposites depends on the load-bearing conditions prevailing at the site of implantation. The storage moduli of the nanocomposites at 37°C approached the lower range of the storage modulus for cortical bone and this may prevent stress shielding during bone regeneration.

Three-dimensional mass spectral imaging of HeLa-M cells--sample preparation, data interpretation and visualisation

Time-of-flight secondary ion mass spectrometry (ToFSIMS) is being applied increasingly to the study of biological systems where the chemical specificity of mass spectrometry and the high lateral resolution imaging capabilities can be exploited. Here we report a comparison of two cell sample preparation methods and demonstrate how they influence the outcome of the ToFSIMS analysis for three-dimensional (3D) imaging of biological cells using our novel buncher-ToF instrument (J105 3D Chemical Imager) equipped with a C(60) primary ion beam. Cells were analysed fixed and freeze-dried and non-fixed, frozen-hydrated. It is concluded that maintaining the cells in a non-fixed frozen-hydrated state during the analysis helps reduce chemical redistribution, producing cleaner spectra and improved chemical contrast in both 2D and 3D imaging. Insights into data interpretation are included and we present methods for 3D reconstruction of the data using multivariate analysis techniques.

Photoprotective energy dissipation involves the reorganization of photosystem II light-harvesting complexes in the grana membranes of spinach chloroplasts

Plants must regulate their use of absorbed light energy on a minute-by-minute basis to maximize the efficiency of photosynthesis and to protect photosystem II (PSII) reaction centers from photooxidative damage. The regulation of light harvesting involves the photoprotective dissipation of excess absorbed light energy in the light-harvesting antenna complexes (LHCs) as heat. Here, we report an investigation into the structural basis of light-harvesting regulation in intact spinach (Spinacia oleracea) chloroplasts using freeze-fracture electron microscopy, combined with laser confocal microscopy employing the fluorescence recovery after photobleaching technique. The results demonstrate that formation of the photoprotective state requires a structural reorganization of the photosynthetic membrane involving dissociation of LHCII from PSII and its aggregation. The structural changes are manifested by a reduced mobility of LHC antenna chlorophyll proteins. It is demonstrated that these changes occur rapidly and reversibly within 5 min of illumination and dark relaxation, are dependent on ΔpH, and are enhanced by the deepoxidation of violaxanthin to zeaxanthin.

Models of membrane-bound Alzheimer's Abeta peptide assemblies

Although it is clear that amyloid beta (Aβ) peptides play a pivotal role in the development of Alzheimer's disease, the precise molecular model of action remains unclear. Aβ peptide forms assemble both in aqueous solution and in lipid membranes. It has been proposed that deleterious effects occur when the peptides interact with membranes, possibly by forming Ca(2+) permeant ion channels. In the accompanying manuscript, we propose models in which the C-terminus third of six Aβ42 peptides forms a six-stranded β-barrel in highly toxic soluble oligomers. Here we extend this hypothesis to membrane-bound assemblies. In these Aβ models, the hydrophobic β-barrel of a hexamer may either reside on the surface of the bilayer, or span the bilayer. Transmembrane pores are proposed to form between several hexamers. Once the β-barrels of six hexamers have spanned the bilayer, they may merge to form a more stable 36-stranded β-barrel. We favor models in which parallel β-barrels formed by N-terminus segments comprise the lining of the pores. These types of models explain why the channels are selective for cations and how metal ions, such as Zn(2+) , synthetic peptides that contain histidines, and some small organic cations may block channels or inhibit formation of channels. Our models were developed to be consistent with microscopy studies of Aβ assemblies in membranes, one of which is presented here for the first time.

Structural changes of the paraflagellar rod during flagellar beating in Trypanosoma cruzi

Background

Trypanosoma cruzi, the agent of Chagas disease, is a protozoan member of the Kinetoplastidae family characterized for the presence of specific and unique structures that are involved in different cell activities. One of them is the paraflagellar rod (PFR), a complex array of filaments connected to the flagellar axoneme. Although the function played by the PFR is not well established, it has been shown that silencing of the synthesis of its major proteins by either knockout of RNAi impairs and/or modifies the flagellar motility.

Methodology/Principal Findings

Here, we present results obtained by atomic force microscopy (AFM) and transmission electron microscopy (TEM) of replicas of quick-frozen, freeze-fractured, deep-etched and rotary-replicated cells to obtain detailed information of the PFR structures in regions of the flagellum in straight and in bent state. The images obtained show that the PFR is not a fixed and static structure. The pattern of organization of the PFR filament network differs between regions of the flagellum in a straight state and those in a bent state. Measurements of the distances between the PFR filaments and the filaments that connect the PFR to the axoneme as well as of the angles between the intercrossed filaments supported this idea.

Conclusions/Significance

Graphic computation based on the information obtained allowed the proposal of an animated model for the PFR structure during flagellar beating and provided a new way of observing PFR filaments during flagellar beating.

Functional reconstitution into liposomes of purified human RhCG ammonia channel

BACKGROUND

Rh glycoproteins (RhAG, RhBG, RhCG) are members of the Amt/Mep/Rh family which facilitate movement of ammonium across plasma membranes. Changes in ammonium transport activity following expression of Rh glycoproteins have been described in different heterologous systems such as yeasts, oocytes and eukaryotic cell lines. However, in these complex systems, a potential contribution of endogenous proteins to this function cannot be excluded. To demonstrate that Rh glycoproteins by themselves transport NH(3), human RhCG was purified to homogeneity and reconstituted into liposomes, giving new insights into its channel functional properties.

METHODOLOGY/PRINCIPAL FINDINGS

An HA-tag introduced in the second extracellular loop of RhCG was used to purify to homogeneity the HA-tagged RhCG glycoprotein from detergent-solubilized recombinant HEK293E cells. Electron microscopy analysis of negatively stained purified RhCG-HA revealed, after image processing, homogeneous particles of 9 nm diameter with a trimeric protein structure. Reconstitution was performed with sphingomyelin, phosphatidylcholine and phosphatidic acid lipids in the presence of the C(12)E(8) detergent which was subsequently removed by Biobeads. Control of protein incorporation was carried out by freeze-fracture electron microscopy. Particle density in liposomes was a function of the Lipid/Protein ratio. When compared to empty liposomes, ammonium permeability was increased two and three fold in RhCG-proteoliposomes, depending on the Lipid/Protein ratio (1/300 and 1/150, respectively). This strong NH(3) transport was reversibly inhibited by mercuric and copper salts and exhibited a low Arrhenius activation energy.

CONCLUSIONS/SIGNIFICANCE

This study allowed the determination of ammonia permeability per RhCG monomer, showing that the apparent Punit(NH3) (around 1x10(-3) microm(3)xs(-1)) is close to the permeability measured in HEK293E cells expressing a recombinant human RhCG (1.60x10(-3) microm(3)xs(-1)), and in human red blood cells endogenously expressing RhAG (2.18x10(-3) microm(3)xs(-1)). The major finding of this study is that RhCG protein is active as an NH(3) channel and that this function does not require any protein partner.

Evaluation of an oral carrier system in rats: bioavailability and antioxidant properties of liposome-encapsulated curcumin

To enhance the curcumin absorption by oral administration, liposome-encapsulated curcumin (LEC) was prepared from commercially available lecithins (SLP-WHITE and SLP-PC70) and examined for its interfacial and biochemical properties. A LEC prepared from 5 wt % of SLP-PC70 and 2.5 wt % of curcumin gave a good dispersibility with 68.0% encapsulation efficiency for curcumin, while those from SLP-WHITE did not. Moreover, the resulting LEC using SLP-PC70 was confirmed to be composed of small unilamellar vesicles with a diameter of approximately 263 nm. The resulting LEC was then examined for its effect on bioavailability in Sprague-Dawley (SD) rats. Three forms of curcumin [curcumin, a mixture of curcumin and SLP-PC70 (lecithin), and LEC] were then administered orally to SD rats at a dose of 100 mg curcumin/kg body weight. The pharmacokinetic parameters following curcumin administration were determined in each form. Pharmacokinetic parameters after oral administration of LEC were compared to those of curcumin and a mixture of curcumin and lecithin. High bioavailability of curcumin was evident in the case of oral LEC; a faster rate and better absorption of curcumin were observed as compared to the other forms. Oral LEC gave higher C(max) and shorter T(max) values, as well as a higher value for the area under the blood concentration-time curve, at all time points. These results indicated that curcumin enhanced the gastrointestinal absorption by liposomes encapsulation. Interestingly, the plasma antioxidant activity following oral LEC was significantly higher than that of the other treatments. In addition, the plasma curcumin concentration was significantly correlated to plasma antioxidant activities, and enhanced curcumin plasma concentrations might exert a stronger influence on food functionality of curcumin. The available information strongly suggests that liposome encapsulation of ingredients such as curcumin may be used as a novel nutrient delivery system.

Ultrastructural disorder of the secretory pathway in temperature-sensitive actin mutants of Saccharomyces cerevisiae

Phenotypes of the two temperature-sensitive actin mutants of Saccharomyces cerevisiae act1-1 and act1-2 at permissive, restrictive and semi-restrictive temperatures were studied by freeze fracture and thin section electron microscopy, and fluorescent microscopy. In contrast to secretory mutants where accumulations of either secretory vesicles, Golgi apparatus, or endoplasmic reticulum were reported, act1-1 and act1-2 mutants revealed accumulation of all the three components, even at permissive temperature. However, more distinct accumulation of secretory organelles was evident during cultivation at the sub-restrictive temperature of 30 degrees C. At the restrictive temperature of 37 degrees C, many cells died, and their empty cell walls remained. Some of the few living cells showed features of apoptosis. From the present study, actin cables are concluded to be necessary for (i) correct spatial positioning and orientation of secretary pathway to the bud and septum, and (ii) vectorial movement of vesicles of the secretory pathway along the actin cables to the bud and septum.

Aggregation behavior of a fluorinated surfactant in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid

The cationic fluorinated surfactant, FC-4, unlike other surfactants, forms micelles in the room temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (bmimTf2N). Surface tension, freeze-fracture transmission electron microscopy, 19F NMR, 1H NMR, and Fourier transform infrared measurements revealed that (i) the FC-4 cation forms an ion pair with the Tf2N anion, (ii) the ion pairs undergo association to form premicellar aggregates, and (iii) the premicellar aggregates transform into micelles at the critical micelle concentration (CMC). The thermodynamic parameters for micelle formation derived from the temperature dependence of the CMC demonstrated that the solvophobic interaction between the solvophobic tails of the surfactant molecules is rather weak in bmimTf2N compared with other ionic liquids, in accordance with the observation that surfactants do not readily form micelles in bmimTf2N. The fact that FC-4 forms micelles in such an inconvenient solvent is attributed to the ion-pair formation between the surfactant cation and the ionic liquid anion.

Self-assembly of double-tail anionic surfactant having cyanobiphenyl terminal groups in water

This study reports the interfacial properties and lyotropic liquid crystal formation of sodium 1,2-bis{6-[4-(4-cyanophenyl)phenyloxy]hexyloxycarbonyl}ethanesulfonate (SBCPHS), which is a double-tail surfactant with cyanobiphenyl terminal groups, in water. Polarized microscopic observation of water/SBCPHS mixtures revealed the presence of columnar and lamellar phases. In the lamellar phase, myelin figures representing multilamellar tubes were observed, and some of these figures had a double-helix structure. In order to examine these liquid crystal structures in detail, the bilayer thickness of the lamellar tubes and the lattice parameters of the columnar phase were measured by small-angle X-ray scattering analysis. Four scattering peaks that could be ascribed to C2/m symmetry were observed for the columnar phase. The bilayer thickness and one of the lattice parameters were smaller than twice the molecular length of SBCPHS; this showed that the liquid crystal phases had intercalated structures. Comparison of SBCPHS with a typical double-tail hydrocarbon surfactant revealed that the cyanobiphenyl terminal groups in the former helped increase the stability of the liquid crystal formed at low temperatures. The stabilizing effect of the cyanobiphenyl terminal groups on the liquid crystals could have been driven by electrostatic intermolecular interactions between the terminal groups in antiparallel arrangement of the SBCPHS molecules.

Distribution of Connexin50 Channels and Hemichannels in Lens Fibers: A Structural Approach

A detailed understanding of the mechanisms regulating cell-to-cell communication in the lens necessitates information about the distribution and density of Cx46 and Cx50 in their native cellular environment. These isoforms constitute the extensive pathway between the lens surface and the interior, helping to maintain its striking optical properties. To identify Cx50 channels and hemichannels in the plasma membrane and to differentiate between them, immuno-freeze-fracture-labeling (FRIL) with immuno-gold particles in used. In equatorial lens fibers, the Cx50-gold complexes label gap junctions at high densities and non-junctional plasma membranes at lower densities. Small depressions in the non-junctional plasma membrane labeled by the gold-complexes most likely represent points of hemichannel insertion. Measurement of the width of the extra-cellular space separating adjacent plasma membranes indicates that the gold complexes in the gap junctions represent Cx50 channels and those in the non-junctional plasma membrane, Cx50 hemichannels. Estimates of their densities indicate that the channels are at least one order of magnitude more numerous than the hemichannels. Therefore, in lens fibers, Cx50 hemichannels are inserted via exocytosis and are rapidly assembled into channels assembled in gap junction plaques.

Molecular adhesion development in a neural cell monolayer forming in an ultrasound trap

A 2-dimensional aggregate of C6 neural cells was formed rapidly (within 30 s) in suspension in a recently developed 1.5 MHz ultrasound standing wave trap. A typical 1 mm diameter aggregate contained about 3,500 cells. Spreading of membrane occurred between the aggregated cells. The rate of spreading of the tangentially developing intercellular contact area was 0.19 microm/min. The form of the suspended aggregate changed from one of a hexagonal arrangement of cells to one of a cell-monolayer-like continuous sheet of mostly quadrilateral and pentagonal cells as in a cell monolayer on a solid substratum. A range of fluorescent indicators showed that the >99% viability of the cells did not change during 1 h exposures; therefore cell viability was not compromised during the monolayer development. The average integral intensities from stained actin filaments at the spreading cell-cell interfaces after 1, 8 and 30 min were 14, 25 and 46 microm(2) respectively. The cells in this work progressed from physical aggregation, through molecular adhesion, to displaying the intracellular consequences of receptor interactions. The ability to form mechanically strong confluent monolayer structures that can be monitored in situ or harvested from the trap provides a technique with general potential for monitoring the synchronous development of cell responses to receptor-triggered adhesion.

The statoconial membrane of the guinea pig utricular macula. Scanning electron microscopic investigation combined with the freeze-fracturing technique

The superstructure of the guinea pig utricular macula was investigated using scanning electron microscopy combined with the freeze-fracturing technique. The statoconial membrane was composed of the otoconial layer, otolithic membrane and subcupular meshwork. The otolithic membrane consisted of closely arranged filaments with beaded appearance and densely packed globular matrix near the otoconial layer. The subcupular meshwork consisted of long branching filaments cross-bridged to one another. The filaments were continuous with those of the otolithic membrane on one side and with the surface of the epithelium on the other, which fills the space between the otolithic membrane and the macular surface. The otolithic membrane would function as a rigid plate and equally distribute the shear force of the otoconial layer to all the ciliary bundles. The subcupular meshwork may play an important role in transmitting the shear strain of the otolithic membrane to all the ciliary bundles and may also exert an additional dampening effect to prevent unwanted vibration.