Function suggests nano-structure: electrophysiology supports that granule membranes play dice

Cellular communication depends on membrane fusion mechanisms. SNARE proteins play a fundamental role in all intracellular fusion reactions associated with the life cycle of secretory vesicles, such as vesicle–vesicle and vesicle plasma membrane fusion at the porosome base in the cell plasma membrane. We present growth and elimination (G&E), a birth and death model for the investigation of granule growth, its evoked and spontaneous secretion and their information content. Using a statistical mechanics approach in which SNARE components are viewed as interacting particles, the G&E model provides a simple ‘nano-machine’ of SNARE self-aggregation behind granule growth and secretion. Results from experimental work, mathematical calculations and statistical modelling suggest that for vesicle growth a minimal aggregation of three SNAREs is required, while for the evoked secretion one SNARE is enough. Furthermore, the required number of SNARE aggregates (which varies between cell types and is nearly proportional to the square root of the mean granule diameter) affects and is statistically identifiable from the size distributions of spontaneous and evoked secreted granules. The new statistical mechanics approach to granule fusion is bound to have a significant changing effect on the investigation of the pathophysiology of secretory mechanisms and methodologies for the investigation of secretion.

Download Full-text

A molecular basis for synexin-driven, calcium-dependent membrane fusion

Journal of Experimental Biology ◽

10.1242/jeb.139.1.267 ◽

1988 ◽

Vol 139 (1) ◽

pp. 267-286

Author(s):

H. B. Pollard ◽

A. L. Burns ◽

E. Rojas

Keyword(s):

Membrane Fusion ◽

Calcium Binding ◽

Plasma Membranes ◽

Cell Types ◽

Complete Analysis ◽

Calcium Dependent ◽

Cell Plasma ◽

Probable Role ◽

Highly Hydrophobic ◽

Chromaffin Granule Ghosts

Membranes of secretory vesicles fuse with each other and with plasma membranes during exocytosis in many different cell types. The probable role of calcium in the process is now widely accepted, and it is possible that at least one cytosolic mediator of calcium action is synexin. Synexin is a 47,000 Mr calcium-binding protein, initially discovered in the bovine adrenal medulla, which binds to granule membranes and to inner aspects of chromaffin cell plasma membranes. Synexin causes chromaffin granules to aggregate, and such aggregates can be caused to fuse in the additional presence of arachidonic acid. Synexin also mediates the direct fusion of liposomes and chromaffin granule ghosts. To understand better the mechanisms of membrane fusion promoted by synexin we have attempted to define the primary sequence of the protein. Our initial efforts were directed towards purification of bovine synexin in sufficient amounts to allow us to sequence tryptic peptides. However, as the project progressed we also directed our attention to human synexin, preparing peptides from this protein as well. From analysis of bovine peptides we learned that the synexin molecule might be closely related to a class of proteins including lipocortin I, calpactin (p36), endonexin II, protein II and calelectrin 67K. Complete analysis of a human synexin cDNA clone revealed strong homology with bovine synexin. The analysis also showed that synexin contained a unique, long, highly hydrophobic N-terminal leader sequence followed by a characteristic four-fold repeat homologous with those found in other members of the synexin gene family. The highly hydrophobic character of synexin seems consistent with information previously obtained that synexin is able to insert directly into the interior of bilayers prepared not only from purified phosphatidylserine but also from biological membranes. The evidence for such insertions is a dramatic increase in the capacitance of the membrane, formed at the tip of a patch pipette, when calcium-activated synexin is applied to the bilayer. Additional evidence is the fact that synexin also forms calcium-selective channels when the protein is applied to the cytosolic aspect of the plasmalemma when that side is also exposed to calcium at sub-millimolar concentrations. Thus, the synexin molecule not only enters the membrane, but also spans it. From these and other data we have developed the concept that the fusion process may involve synexin forming a ‘hydrophobic bridge’ between two fusing membranes. Lipid movement across this bridge may then be the material basis for final fusion.(ABSTRACT TRUNCATED AT 400 WORDS)

Download Full-text

Studies of membrane fusion. IV. Fusion of HeLa cells with Sendai virus

Journal of Cell Science ◽

10.1242/jcs.36.1.73 ◽

1979 ◽

Vol 36 (1) ◽

pp. 73-84

Author(s):

S. Knutton

Keyword(s):

Plasma Membrane ◽

Membrane Fusion ◽

Cell Fusion ◽

Hela Cells ◽

Sendai Virus ◽

Freeze Fracture ◽

Viral Envelope ◽

Cell Plasma Membrane ◽

Virus Particles ◽

Cell Plasma

The Sendai virus-induced fusion of HeLa cells has been studied by freeze-fracture electron microscopy. Freeze-fracture observations confirm previous scanning electron-microscope studies (1977) and show that at 4 degrees C virus particles bind to the cell surface and that cell agglutination results from the crosslinking by virus particles of microvilli on adjacent cells. Incubation at 37 degrees C initiates a change in viral envelope structure and fusion of ‘altered’ virus particles with the cell plasma membrane. Fusion of a virus particle with two crosslinked cells is probably the membrane fusion event which initiates cell-cell fusion; fusion is completed as a result of virally induced cell swelling. Lateral diffusion of viral envelope components following virus-cell fusion and, in some instances, an aggregation of plasma membrane intramembrane particles occurs in swollen cells. These observations show that the mechanisms of viral envelope-cell and probably cell-cell fusion are the same as have been reported for erythrocytes. Although endocytosis of intact virus particles does occur, the specialized cell-mediated mechanism for fusion of the viral envelope with the cell plasma membrane suggests that this, and not viropexis, is the mechanism of Sendai virus infection.

Download Full-text

Breaking Biological Barriers with a Toothbrush

Journal of Dental Research ◽

10.1177/154405910708600816 ◽

2007 ◽

Vol 86 (8) ◽

pp. 769-774 ◽

Cited By ~ 7

Author(s):

K. Amano ◽

K. Miyake ◽

J.L. Borke ◽

P.L. McNeil

Keyword(s):

Skeletal Muscle ◽

Plasma Membrane ◽

Oral Cavity ◽

Cell Types ◽

Tissue Architecture ◽

Cell Plasma Membrane ◽

Epithelial Barrier Function ◽

Gingival Health ◽

Cell Plasma ◽

Gingival Epithelium

Toothbrushing exposes epithelia and other tissues of the oral cavity to mechanical stress. Here, we investigated whether brushing induces cell wounding—plasma membrane disruption—in epithelial and other cell types in the oral cavity. Brushing of the gingivae and tongues of rats resulted in a striking increase in the number of cells positive for a marker of disruption injury. These cells included those in all strata of the gingival epithelium, and in the skeletal muscle of the tongue. Additionally, we found that brushing resulted in an increase in c-fos expression by junctional epithelial and skeletal muscle cells. Epithelial barrier function, however, was not overtly affected by brushing, despite the observed individual injuries to cells. We concluded that brushing disrupts cell plasma membrane barriers in the oral cavity and activates gene expression events that may lead to local adaptive changes in tissue architecture beneficial to gingival health.

Download Full-text

Membrane microdomains: lessons from microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100140257 ◽

1995 ◽

Vol 53 ◽

pp. 776-777

Author(s):

J.M. Robinson ◽

J.M Oliver

Keyword(s):

Spatial Distribution ◽

Plasma Membrane ◽

Epithelial Cells ◽

Plasma Membranes ◽

Cell Types ◽

Imaging Modalities ◽

Membrane Microdomains ◽

Membrane Domains ◽

Lateral Heterogeneity ◽

Functional Importance

Specialized regions of plasma membranes displaying lateral heterogeneity are the focus of this Symposium. Specialized membrane domains are known for certain cell types such as differentiated epithelial cells where lateral heterogeneity in lipids and proteins exists between the apical and basolateral portions of the plasma membrane. Lateral heterogeneity and the presence of microdomains in membranes that are uniform in appearance have been more difficult to establish. Nonetheless a number of studies have provided evidence for membrane microdomains and indicated a functional importance for these structures.This symposium will focus on the use of various imaging modalities and related approaches to define membrane microdomains in a number of cell types. The importance of existing as well as emerging imaging technologies for use in the elucidation of membrane microdomains will be highlighted. The organization of membrane microdomains in terms of dimensions and spatial distribution is of considerable interest and will be addressed in this Symposium.

Download Full-text

Multimodal Atomic Force Imaging of Open Hemichannelinduced Modulation of Cell Volume and Viscoelastic Properties

Microscopy and Microanalysis ◽

10.1017/s1431927600018316 ◽

1999 ◽

Vol 5 (S2) ◽

pp. 998-999

Author(s):

Seung K. Rhee ◽

Arjan P. Quist ◽

Hai Lin ◽

Nils Almqvist ◽

Ratneshx Lai

Keyword(s):

Plasma Membrane ◽

Cell Volume ◽

Lucifer Yellow ◽

Single Cells ◽

Dye Uptake ◽

Aortic Endothelial Cells ◽

Atomic Force ◽

Cell Plasma ◽

Uptake Assay ◽

Gap Junctional

Hemichannels from two single cells can join upon contact between these cells to form gap junctions - an intercellular pathway for the direct exchange of ions and small metabolites. Using techniques of fluorescent dye-uptake assay, laser confocal fluorescence imaging and atomic force microscopy (AFM), we have examined the role of hemichannels, present in the non-junctional regions of single cell plasma membrane, in the modulation of cell volume.Antibodies against a gap junctional protein connexin43, were immunolocalized to nonjunctional plasma membrane regions of single BICR-MlRk k (breast tumor epithelial) cells, KOM-1 (bovine aortic endothelial) cells, and GM04260 (AD-free human) fibroblast cells. In the absence of extracellular calcium, cytoplasmic uptake of Lucifer yellow (LY) but not of dextran-conjugated LY was observed in single cells. Dye uptake was prevented by gap junctional inhibitors, ẞ-glycyrrhetinic acid (ẞGCA) and oleamide.

Download Full-text

The exosome journey: from biogenesis to uptake and intracellular signalling

Cell Communication and Signaling ◽

10.1186/s12964-021-00730-1 ◽

2021 ◽

Vol 19 (1) ◽

Author(s):

Sonam Gurung ◽

Dany Perocheau ◽

Loukia Touramanidou ◽

Julien Baruteau

Keyword(s):

Clinical Trials ◽

Plasma Membrane ◽

Scientific Community ◽

Cell Types ◽

Clinical Applications ◽

Clinical Development ◽

Intracellular Signalling ◽

Clinical Settings ◽

Health And Disease ◽

Adequate Definition

AbstractThe use of exosomes in clinical settings is progressively becoming a reality, as clinical trials testing exosomes for diagnostic and therapeutic applications are generating remarkable interest from the scientific community and investors. Exosomes are small extracellular vesicles secreted by all cell types playing intercellular communication roles in health and disease by transferring cellular cargoes such as functional proteins, metabolites and nucleic acids to recipient cells. An in-depth understanding of exosome biology is therefore essential to ensure clinical development of exosome based investigational therapeutic products. Here we summarise the most up-to-date knowkedge about the complex biological journey of exosomes from biogenesis and secretion, transport and uptake to their intracellular signalling. We delineate the major pathways and molecular players that influence each step of exosome physiology, highlighting the routes of interest, which will be of benefit to exosome manipulation and engineering. We highlight the main controversies in the field of exosome research: their adequate definition, characterisation and biogenesis at plasma membrane. We also delineate the most common identified pitfalls affecting exosome research and development. Unravelling exosome physiology is key to their ultimate progression towards clinical applications.

Download Full-text

Plasma membrane integrity in health and disease: significance and therapeutic potential

Cell Discovery ◽

10.1038/s41421-020-00233-2 ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Catarina Dias ◽

Jesper Nylandsted

Keyword(s):

Plasma Membrane ◽

Therapeutic Potential ◽

Calcium Influx ◽

Membrane Integrity ◽

Cell Types ◽

Physical Parameters ◽

Membrane Repair ◽

Plasma Membrane Integrity ◽

Repair Mechanisms ◽

And Function

AbstractMaintenance of plasma membrane integrity is essential for normal cell viability and function. Thus, robust membrane repair mechanisms have evolved to counteract the eminent threat of a torn plasma membrane. Different repair mechanisms and the bio-physical parameters required for efficient repair are now emerging from different research groups. However, less is known about when these mechanisms come into play. This review focuses on the existence of membrane disruptions and repair mechanisms in both physiological and pathological conditions, and across multiple cell types, albeit to different degrees. Fundamentally, irrespective of the source of membrane disruption, aberrant calcium influx is the common stimulus that activates the membrane repair response. Inadequate repair responses can tip the balance between physiology and pathology, highlighting the significance of plasma membrane integrity. For example, an over-activated repair response can promote cancer invasion, while the inability to efficiently repair membrane can drive neurodegeneration and muscular dystrophies. The interdisciplinary view explored here emphasises the widespread potential of targeting plasma membrane repair mechanisms for therapeutic purposes.

Download Full-text

Stimulation of Tumor-Specific Immunity Using Tumor Cell Plasma Membrane Antigen

Methods ◽

10.1006/meth.1997.0466 ◽

1997 ◽

Vol 12 (2) ◽

pp. 155-164 ◽

Cited By ~ 9

Author(s):

Matthew F Mescher ◽

Elena Savelieva

Keyword(s):

Plasma Membrane ◽

Tumor Cell ◽

Cell Plasma Membrane ◽

Specific Immunity ◽

Cell Plasma ◽

Stimulation Of

Download Full-text

Charged anaesthetics alter LM-fibroblast plasma-membrane enzymes by selective fluidization of inner or outer membrane leaflets

Biochemical Journal ◽

10.1042/bj2390301 ◽

1986 ◽

Vol 239 (2) ◽

pp. 301-310 ◽

Cited By ~ 31

Author(s):

W D Sweet ◽

F Schroeder

Keyword(s):

Plasma Membrane ◽

Active Site ◽

Plasma Membranes ◽

Local Anaesthetics ◽

Cationic Drugs ◽

Cell Plasma ◽

Composition And Structure ◽

Highly Sensitive ◽

Functional Consequences ◽

Anionic Drugs

The functional consequences of the differences in lipid composition and structure between the two leaflets of the plasma membrane were investigated. Fluorescence of 1,6-diphenylhexa-1,3,5-triene(DPH), quenching, and differential polarized phase fluorimetry demonstrated selective fluidization by local anaesthetics of individual leaflets in isolated LM-cell plasma membranes. As measured by decreased limiting anisotropy of DPH fluorescence, cationic (prilocaine) and anionic (phenobarbital and pentobarbital) amphipaths preferentially fluidized the cytofacial and exofacial leaflets respectively. Unlike prilocaine, procaine, also a cation, fluidized both leaflets of these membranes equally. Pentobarbital stimulated 5′-nucleotidase between 0.1 and 5 mM and inhibited at higher concentrations, whereas phenobarbital only inhibited, at higher concentrations. Cationic drugs were ineffective. Two maxima of (Na+ + K+)-ATPase activation were obtained with both anionic drugs. Only one activation maximum was obtained with both cationic drugs. The maximum in activity below 1 mM for all four drugs clustered about a single limiting anisotropy value in the cytofacial leaflet, whereas there was no correlation between activity and limiting anisotropy in the exofacial leaflets. Therefore, although phenobarbital and pentobarbital below 1 mM fluidized the exofacial leaflet more than the cytofacial leaflet, the smaller fluidization in the cytofacial leaflet was functionally significant for (Na+ + K+)-ATPase. Mg2+-ATPase was stimulated at 1 mM-phenobarbital, unaffected by pentobarbital and slightly stimulated by both cationic drugs at concentrations fluidizing both leaflets. Thus the activity of (Na+ + K+)-ATPase was highly sensitive to selective fluidization of the leaflet containing its active site, whereas the other enzymes examined were little affected by fluidization of either leaflet.

Download Full-text