Power transmission along biological membranes

Hypothesis on long-distance power transmission along extended energy-transducing membranes (Skulachev, 1969, 1971, 1980), has been experimentally proven in four different systems, namely, (i) trichomes of filamentous cyanobacterium Phormidium uncinatum; (ii) filamentous mitochondria and mitochondrial network in fibroblasts; (iii) clusters of roundish heart muscle mitochondria interconnected with mitochondrial junctions; (iv) mixed animal cell cultures interconnected with gap junctions. In all cases, energy was shown to be transmitted in the form of a transmembrane electric potential difference. The transmission occurred for distances as long as several tens of micrometers. Since the (a) delta-muH-bearing cytoplasmic membrane of cyanobacteria and the inner mitochondrial membrane and (b) delta-muNa-bearing outer animal cell membrane were found to be competent in such an effect, one may assume that the power transmission is a fundamental function of extended membrane systems. This mechanism can be used at the intracellular level (mitochondrial) as well as at the supracellular level (cytoplasmic and outer cell membranes). Studies on the possible involvement of membranes in lateral transport of oxygen, ions, fatty acids and membrane proteins seem to hold good promise.     

Membrane invagination in Rhodobacter sphaeroides is initiated at curved regions of the cytoplasmic membrane,then forms both budded and fully detached spherical vesicles

The purple phototrophic bacteria synthesize an extensive system of intracytoplasmic membranes (ICM) in order to increase the surface area for absorbing and utilizing solar energy. Rhodobacter sphaeroides cells contain curved membrane invaginations. In order to study the biogenesis of ICM in this bacterium mature (ICM) and precursor (upper pigmented band – UPB) membranes were purified and compared at the single membrane level using electron, atomic force and fluorescence microscopy, revealing fundamental differences in their morphology, protein organization and function. Cryo‐electron tomography demonstrates the complexity of the ICM of Rba. sphaeroides. Some ICM vesicles have no connection with other structures, others are found nearer to the cytoplasmic membrane (CM), often forming interconnected structures that retain a connection to the CM, and possibly having access to the periplasmic space. Near‐spherical single invaginations are also observed, still attached to the CM by a ‘neck’. Small indents of the CM are also seen, which are proposed to give rise to the UPB precursor membranes upon cell disruption. ‘Free‐living’ ICM vesicles, which possess all the machinery for converting light energy into ATP, can be regarded as bacterial membrane organelles.     

Ultrastructural changes in Blastomyces dermatitidis after in vitro exposure to lidocaine

Electron microscopic examination of yeasts of Blastomyces dermatitidis, exposed in vitro to concentrations of lidocaine that occur when the drug is used for topical anesthesia, showed that lidocaine rapidly damaged intracellular structures. The extent of damage was dependent on the concentration of drug and length of exposure. The observed ultrastructural changes were very similar to those reported for other drugs that directly damage membranes. This relationship suggests that the antifungal effect of lidocaine is the result of direct membrane damage.     

ORGANIZATION AND BREAKDOWN OF THE PROTOPLAST DURING MATURATION OF PINE TRACHEIDS

The protoplast of maturing axial tracheids in the secondary xylem of shortleaf pine (Pinus echinata Mill.) was studied by transmission and scanning electron microscopy. The mature protoplast is differentiated into two interconnected components: (1) the commonly observed peripheral layer lining the secondary cell wall, and (2) an elaborate reticulum of cytoplasmic filaments and placoids within the central vacuole. The reticulum provides an extensive surface area of vacuolar membranes for rapid exchange of nutrients and metabolites with the vacuolar sap, which is envisaged to function as a vital medium during the period of secondary cell wall synthesis. The breakdown of the protoplast which terminates tracheid maturation is associated with poorly defined alterations of the vacuolar membranes. This is indicated by increased formation of cytoplasmic spherules and membraneous vesicles which may be portions of separated vacuolar membrane during early stages of degradation. Autolysis is supposed to occur when the cytoplasm is exposed to the vacuolar sap after rupture and separation of the vacuolar membranes. The Gomori acid phosphatase technique as combined with electron microscopy produced no evidence of autolysosomal segresomes in strands of intravacuolar reticulum of the cytoplasm.     

Active mechanisms are needed to describe cell responses to submicrosecond, megavolt-per-meter pulses: cell models for ultrashort pulses

Intracellular effects of submicrosecond, megavolt-per-meter pulses imply changes in a cell's plasma membrane (PM) and organelle membranes. The maximum reported PM transmembrane voltage is only 1.6 V and phosphatidylserine is translocated to the outer membrane leaflet of the PM. Passive membrane models involve only displacement currents and predict excessive PM voltages (∼25 V). Here we use a cell system model with nonconcentric circular PM and organelle membranes to demonstrate fundamental differences between active (nonlinear) and passive (linear) models. We assign active or passive interactions to local membrane regions. The resulting cell system model involves a large number of interconnected local models that individually represent the 1), passive conductive and dielectric properties of aqueous electrolytes and membranes; 2), resting potential source; and 3), asymptotic membrane electroporation model. Systems with passive interactions cannot account for key experimental observations. Our active models exhibit supra-electroporation of the PM and organelle membranes, some key features of the transmembrane voltage, high densities of small pores in the PM and organelle membranes, and a global postpulse perturbation in which cell membranes are depolarized on the timescale of pore lifetimes.     

Absence of plasma membrane H+-ATPase in plasmodesmata located in pit-fields of the young reactive pulvinus ofMimosa pudica L.

Summary Immunocytochemical techniques were employed to study the spatial distribution of the plasma membrane H⁺-ATPase within various cell types of the young reactive primary pulvinus ofMimosa pudica L. These cells were interconnected by large numbers of plasmodesmata, being concentrated within pit-fields. Although we could routinely detect evidence of the H⁺-ATPase along the plasma membrane, immunolabelling was rarely, if ever, observed along the plasma membranes of the plasmodesmata. This finding is discussed with respect to the likely specialized supramolecular structure of the plasmodesma.Abbreviations SEL size exclusion limit of plasmodesmata     

Cytokinesis and nodal anatomy in the charophycean green algaChara zeylanica

Summary Cell plate formation inChara zeylanica was compared with recent models of cytokinesis in higher plants in order to gain insight into the evolutionary origin of plant cytokinetic processes. Transmission electron microscopy (TEM) reveals that while cytokinesis inC. zeylanica bears many features in common with that in higher plants, there are significant differences. Unlike that in higher plants, cytokinesis inC. zeylanica begins with a congregation of smooth membrane tubules that are closely associated with endoplasmic reticulum (ER) and Golgi membranes. Mitochondria and other organelles excluded by the phragmoplast in higher plants are present as well. Unlike in higher plants, phragmoplast microtubules persist throughout cytokinesis inC. zeylanica, and the cell plate generally forms across the whole cell at once, though development is patchy, due to small regions developing at different rates; the ends of the plate form last. By identifying aspects of cytokinesis that are different inC. zeylanica and plants, our study indicates which cytokinetic features are more likely to be derived, and which are more likely to be ancestral. In addition, we demonstrated that all nodal cells ofC. zeylanica are interconnected via plasmodesmata, lending support to the idea that, whileChara spp. are generally considered to be filamentous organisms, nodal regions may be thought of as meristemlike tissues.Abbreviations HPF high-pressure freezing - KFe potassium ferricyanide - SCF stepwise chemical fixation - TEM transmission electron microscopy     

The growth and partition of cell membranes during synchronized division cycle of Caulobacter crescentus

Summary The growth and division of cell membranes in Caulobacter crescentus has been studied. This microorganism divides into flagellated and stalked cells which are easily separated by centrifugation. The biosynthesis and partition of membranes was studied by labeling the proteins with [³H]-leucine and the lipids with [³²P]. The membranes were prepared from cell spheroplasts. They further purified on a sucrose gradient.The data obtained show changes of the rate of synthesis of membranes in C. crescentus during the first synchronized division cycle (110 min): the rate is faster in the first 70 min and it drops by 26% during the following 40 min. During the period of faster synthesis the flagellated cells are changing into stalked cells while doubling in size.There is also an intracellular pool of membrane precursors the quantity of which almost doubles as the rate of membrane synthesis decreases, i.e., before cell division.The macromolecules constituting the membranes are not degraded.After division, in each membrane of the two morphologically different cell types the specific radioactivity is 50% of that of the parent cell membranes.     

The extreme longevity of Arctica islandica is associated with increased peroxidation resistance in mitochondrial membranes

The deleterious reactive carbonyls released upon oxidation of polyunsaturated fatty acids in biological membranes are believed to foster cellular aging. Comparative studies in mammals and birds have shown that the susceptibility to peroxidation of membrane lipids peroxidation index (PI) is negatively correlated with longevity. Long‐living marine molluscs are increasingly studied as longevity models, and the presence of different types of lipids in the membranes of these organisms raises questions on the existence of a PI–longevity relationship. We address this question by comparing the longest living metazoan species, the mud clam Arctica islandica (maximum reported longevity = 507 year) to four other sympatric bivalve molluscs greatly differing in longevity (28, 37, 92, and 106 year). We contrasted the acyl and alkenyl chain composition of phospholipids from the mitochondrial membranes of these species. The analysis was reproduced in parallel for a mix of other cell membranes to investigate whether a different PI–longevity relationship would be found. The mitochondrial membrane PI was found to have an exponential decrease with increasing longevity among species and is significantly lower for A. islandica. The PI of other cell membranes showed a linear decrease with increasing longevity among species and was also significantly lower for A. islandica. These results clearly demonstrate that the PI also decreases with increasing longevity in marine bivalves and that it decreases faster in the mitochondrial membrane than in other membranes in general. Furthermore, the particularly low PI values for A. islandica can partly explain this species’ extreme longevity.     

Take the tube: remodelling of the endosomal system by intracellular Salmonella enterica

Salmonella enterica is a facultative intracellular pathogen residing in a unique host cell‐derived membrane compartment, termed Salmonella‐containing vacuole or SCV. By the activity of effector proteins translocated by the SPI2‐endoced type III secretion system (T3SS), the biogenesis of the SCV is manipulated to generate a habitat permissive for intracellular proliferation. By taking control of the host cell vesicle fusion machinery, intracellular Salmonella creates an extensive interconnected system of tubular membranes arising from vesicles of various origins, collectively termed Salmonella‐induced tubules (SIT). Recent work investigated the dynamic properties of these manipulations. New host cell targets of SPI2‐T3SS effector proteins were identified. By applying combinations of live cell imaging and ultrastructural analyses, the detailed organization of membrane compartments inhabited and modified by intracellular Salmonella is now available. These studies provided unexpected new details on the intracellular environments of Salmonella. For example, one kind of SIT, the LAMP1‐positive Salmonella‐induced filaments (SIF), are composed of double‐membrane tubules, with an inner lumen containing host cell cytosol and cytoskeletal filaments, and an outer lumen containing endocytosed cargo. The novel findings call for new models for the biogenesis of SCV and SIT and give raise to many open questions we discuss in this review.     

ULTRASTRUCTURE OF THE PYRENOID OF TREBOUXIA IN RAMALINA MENZIESII TUCK.1,2

Trebouxia sp., the phycobiont of the lichen Ramalina menziesii Tuck., was examined with the electron microscope. Its pyrenoid is characterized structurally as being permeated by interconnected vesiculate membrane systems associated with osmiophilic globules termed pyrenoglobuli. The variety of membrane structure associated with the pyrenoid has been documented with electron micrographs. A model based on serial sections was constructed to show the extent of vesiculation, to demonstrate that the pyrenoglobuli within the pyrenoid matrix are invariably adjacent to the thylakoid membranes within that, matrix, and to emphasize the recurrent thylakoid membrane to pyrenoglobuli relationship. A comparison of the glutaraldehyde-osmium fixation image of the pyrenoglobuli and pyrenoid matrix with the permanganate fixation image has been included. The structure of the pyrenoid matrix in thin section was examined and appears essentially granular.     

Membrane Dynamics of the Contractile Vacuole Complex of Paramecium1

ABSTRACT. Membrane dynamics of the contractile vacuole complex of Paramecium were investigated using conventional electron microscopy of cells so that the vacuoles were serial-sectioned longitudinally and transversely. During systole, vacuolar membrane collapses first into flattened cisternae which undergo further modification into a mass of interconnected small membrane tubules. These tubules retain their connections with the radiating microtubular ribbons; consequently they are found only in the poleward hemisphere. Permanent connections between ampullae and the collapsed vacuole membrane could not be verified nor was a sphincter-like mechanism for closing such a junction observed. Membranes of the ampullae and the collecting canals also collapse to varying extents into arrays of tubules that remain bound to microtubular ribbons during diastole. Thus vacuole, ampullae, and collecting canal membranes all assume tubular forms when internal volume is at a minimum. Having failed to observe a microfilamentous encasement of the vacuole, we suggest that an alternative mechanism for the “contractile” function should be sought. One such is based on fluid volume increase and fluid flow within transiently interconnected tubular membrane systems that cycle between a tubular and a planar membrane form as internal volume is periodically increased and reduced. The driving force for this mechanism might best be sought in the molecular structure of the membranes of the contractile vacuole complex.     

Electron tomographic characterization of a vacuolar reticulum and of six vesicle types that occupy different cytoplasmic domains in the apex of tip-growing <Emphasis Type="Italic">Chara</Emphasis> rhizoids

We provide a 3D ultrastructural analysis of the membrane systems involved in tip growth of rhizoids of the green alga Chara. Electron tomography of cells preserved by high-pressure freeze fixation has enabled us to distinguish six different types of vesicles in the apical cytoplasm where the tip growth machinery is accommodated. The vesicle types are: dark and light secretory vesicles, plasma membrane-associated clathrin-coated vesicles (PM-CCVs), Spitzenkoerper-associated clathrin-coated vesicles (Sp-CCVs) and coated vesicles (Sp-CVs), and microvesicles. Each of these vesicle types exhibits a distinct distribution pattern, which provides insights into their possible function for tip growth. The PM-CCVs are confined to the cytoplasm adjacent to the apical plasma membrane. Within this space they are arranged in clusters often surrounding tubular plasma membrane invaginations from which CCVs bud. This suggests that endocytosis and membrane recycling are locally confined to specialized apical endocytosis sites. In contrast, exocytosis of secretory vesicles occurs over the entire membrane area of the apical dome. The Sp-CCVs and the Sp-CVs are associated with the aggregate of endoplasmic reticulum membranes in the center of the growth-organizing Spitzenkoerper complex. Here, Sp-CCVs are seen to bud from undefined tubular membranes. The subapical region of rhizoids contains a vacuolar reticulum that extends along the longitudinal cell axis and consists of large, vesicle-like segments interconnected by thin tubular domains. The tubular domains are encompassed by thin filamentous structures resembling dynamin spirals which could drive peristaltic movements of the vacuolar reticulum similar to those observed in fungal hyphae. The vacuolar reticulum appears to serve as a lytic compartment into which multivesicular bodies deliver their internal vesicles for molecular recycling and degradation. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Studies on the endoplasmic reticulum. II. Simple dispositions in cells in situ

A survey of a large number of different cell types has indicated the presence of a network of membrane-bound cavities (the endoplasmic reticulum) in the cytoplasm of all cell types examined, with the exception of the mature erythrocyte. In its simplest form, encountered in seminal epithelia and in leucocytes, the reticulum consists mainly of interconnected strings of vesicles and appears to be randomly disposed in three dimensions. Local differentiations occur within the endoplasmic reticulum of all the cell types studied. The membrane limiting the cavities of the endoplasmic reticulum appears to be continuous with the cell membrane and the nuclear membranes.     

A novel membrane anchor for FtsZ is linked to cell wall hydrolysis in Caulobacter crescentus

In most bacteria, the tubulin‐like GTPase FtsZ forms an annulus at midcell (the Z‐ring) which recruits the division machinery and regulates cell wall remodeling. Although both activities require membrane attachment of FtsZ, few membrane anchors have been characterized. FtsA is considered to be the primary membrane tether for FtsZ in bacteria, however in Caulobacter crescentus, FtsA arrives at midcell after stable Z‐ring assembly and early FtsZ‐directed cell wall synthesis. We hypothesized that additional proteins tether FtsZ to the membrane and demonstrate that in C. crescentus, FzlC is one such membrane anchor. FzlC associates with membranes directly in vivo and in vitro and recruits FtsZ to membranes in vitro. As for most known membrane anchors, the C‐terminal peptide of FtsZ is required for its recruitment to membranes by FzlC in vitro and midcell recruitment of FzlC in cells. In vivo, overproduction of FzlC causes cytokinesis defects whereas deletion of fzlC causes synthetic defects with dipM, ftsE and amiC mutants, implicating FzlC in cell wall hydrolysis. Our characterization of FzlC as a novel membrane anchor for FtsZ expands our understanding of FtsZ regulators and establishes a role for membrane‐anchored FtsZ in the regulation of cell wall hydrolysis.     

Protein 4.1B in mouse islets of Langerhans and β-cell tumorigenesis

Protein 4.1 family proteins are thought to interact with membrane proteins and membrane skeletons. Immunohistochemical studies by light and electron microscopy were performed on mouse pancreas with a specific antibody against protein 4.1B. Specific protein 4.1B immunolabeling was observed on endocrine cells in the islets of Langerhans. Protein 4.1B localized along the plasma membranes facing adjacent cells. By immunoelectron microscopy, the immunolabeling of the cells was restricted to the cytoplasmic side just beneath their plasma membrane, including the membranes adjacent to neighboring cells, while the plasma membranes facing endothelial cells were not immunolabeled for protein 4.1B. The immunolocalization of E-cadherin was similar, if not identical, to that of protein 4.1B supporting the idea that protein 4.1B may be functionally interconnected with adhesion molecules. In a transgenic mouse model of pancreatic -cell carcinogenesis (Rip1Tag2), the loss of protein 4.1B expression coincided with the phenotypic transition from adenoma to carcinoma. Therefore, we propose a role of protein 4.1B as a connecting and/or signaling molecule between membrane architecture, cell adhesion, and tumor cell invasion in mouse pancreatic endocrine cells.     

STUDIES ON THE ENDOPLASMIC RETICULUM : II. SIMPLE DISPOSITIONS IN CELLS IN SITU

A survey of a large number of different cell types has indicated the presence of a network of membrane-bound cavities (the endoplasmic reticulum) in the cytoplasm of all cell types examined, with the exception of the mature erythrocyte. In its simplest form, encountered in seminal epithelia and in leucocytes, the reticulum consists mainly of interconnected strings of vesicles and appears to be randomly disposed in three dimensions. Local differentiations occur within the endoplasmic reticulum of all the cell types studied. The membrane limiting the cavities of the endoplasmic reticulum appears to be continuous with the cell membrane and the nuclear membranes.     

Assembly,stability and integrity of basement membranes in vivo

Basement membranes are layered structures of the extracellular matrix which separate cells of various kinds from the surrounding stroma. One of the frequently recurring questions about basement membranes is how these structures are formed in vivo. Up to a few years ago, it was thought that basement membranes were formed spontaneously by a process of self-assembly of their components. However, it has now become clear that cell membrane receptors for basement membrane components are essential factors for the formation and stability of basement membranes in vivo. The present review highlights the modern concepts of basement membrane formation.     

STUDIES ON AN EPITHELIAL (GLAND) CELL JUNCTION : II. Surface Structure

The surface structure of a gland epithelium (Drosophila salivary gland), particularly that at the junction between cells, was examined under the electron microscope. The junctional surface, which in the preceding paper was shown to be highly permeable to ions, has the following structural characteristics. About two-thirds of it are profusely infolded; the surface membranes of adjoining cells interdigitate and present desmosomes. The width of the intercellular space varies considerably. The remainder of the junctional surface, the third that abuts on the lumen, is rather straight. Here, the cell membranes are aligned parallel at a distance of 150 A, and interconnected at regular intervals of 100 A. The connecting material has a high electron opacity, and is about as thick as the cell membranes, but, unlike the latter, has no resolvable unit membrane structure. The surface at the cell base, which in the preceding paper was shown to be rather impermeable, is infolded and resembles the infolded junctional region. The luminal surface exhibits microvilli. Critical surface dimensions are given, and the implications of surface structure in intercellular permeability are discussed.     

Structural differentiation of membranes involved in the secretion of polysaccharide slime by root cap cells of cress (Lepidium sativum L.)

The peripheral secretion tissue of the root cap of Lepidium sativum L. was investigated by electronmicroscopy and freeze-fracturing in order to study structural changes of membranes involved in the secretion process of polysaccharide slime. Exocytosis of slime-transporting vesicles occurs chiefly in the distal region of the anticlinal cell walls. The protoplasmic fracture face (PF) of the plasmalemma of this region is characterized by a high number of homogenously distributed intramembranous particles (IMPs) interrupted by areas nearly free of IMPs. Near such areas slime-transporting vesicles are found to be underlying the plasma membrane. It can be concluded that areas poor in particles are prospective sites for membrane fusion. During the formation of slime-transporting vesicles, the number of IMPs undergoes a striking change in the PF of dictyosome membranes and their derivatives. It is high in dictyosome cisternae and remarkably lower in the budding region at the periphery of the cisternae. Slime-transporting vesicles are as poor in IMPs as the areas of the plasmalemma. Microvesicles rich in IMPs are observed in the surroundings of dictyosomes. The results indicate that in the plasmalemma and in membranes of the Golgi apparatus special classes of proteins — recognizable as IMPs — are displaced laterally into adjacent membrane regions. Since the exoplasmic fracture face (EF) of these membranes is principally poor in particles, it can be concluded that membrane fusion occurs in areas characterized by a high quantity of lipid molecules. It is obvious that the Golgi apparatus regulates the molecular composition of the plasma membrane by selection of specific membrane components. The drastic membrane transformation during the formation of slime-transporting vesicles in the Golgi apparatus causes the enrichment of dictyosome membranes by IMPs, whereas the plasma membrane probably is enriched by lipids. The structural differentiations in both the plasma membrane and in Golgi membranes are discussed in relation to membrane transformation, membrane flow, membrane fusion, and recycling of membrane constituents.Abbreviations PF protoplasmic fracture face - EF exoplasmic fracture face - IMP intramembranous particle