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Molecular Biology of the Cell Jan 2019Crowding of the subcellular environment by macromolecules is thought to promote protein aggregation and phase separation. A challenge is how to parameterize the degree... (Review)
Review
Crowding of the subcellular environment by macromolecules is thought to promote protein aggregation and phase separation. A challenge is how to parameterize the degree of crowding of the cell interior or artificial solutions that is relevant to these reactions. Here I review colloid osmotic pressure as a crowding metric. This pressure is generated by solutions of macromolecules in contact with pores that are permeable to water and ions but not macromolecules. It generates depletion forces that push macromolecules together in crowded solutions and thus promotes aggregation and phase separation. I discuss measurements of colloid osmotic pressure inside cells using the nucleus, the cytoplasmic gel, and fluorescence resonant energy transfer (FRET) biosensors as osmometers, which return a range of values from 1 to 20 kPa. I argue for a low value, 1-2 kPa, in frog eggs and perhaps more generally. This value is close to the linear range on concentration-pressure curves and is thus not crowded from an osmotic perspective. I discuss the implications of a low crowding pressure inside cells for phase separation biology, buffer design, and proteome evolution. I also discuss a pressure-tension model for nuclear shape, where colloid osmotic pressure generated by nuclear protein import inflates the nucleus.
Topics: Animals; Colloids; Hydrodynamics; Macromolecular Substances; Models, Biological; Osmosis; Subcellular Fractions
PubMed: 30640588
DOI: 10.1091/mbc.E18-09-0549 -
Water Research Apr 2020High-pressure membrane filtration (reverse osmosis and nanofiltration) is used to purify different water sources, including wastewater, surface water, groundwater and... (Review)
Review
High-pressure membrane filtration (reverse osmosis and nanofiltration) is used to purify different water sources, including wastewater, surface water, groundwater and seawater. A major concern in membrane filtration is the accumulation and growth of micro-organisms and their secreted polymeric substances, leading to reduced membrane performance and membrane biofouling. The fundamental understanding of membrane biofouling is limited despite years of research, as the means of microbial interactions and response to the conditions on the membrane surface are complicated. Here, we discuss studies that investigated the microbial diversity of fouled high-pressure membranes. High-throughput amplicon sequencing of the 16S rRNA gene have shown that Burkholderiales, Pseudomonadales, Rhizobiales, Sphingomonadales and Xanthomonadales frequently obtain a high relative abundance on fouled membranes. The bacterial communities present in the diverse feed water types and in pre-treatment compartments are different from the communities on the membrane, because high-pressure membrane filtration provides a selective environment for certain bacterial groups. The biofilms that form within the pre-treatment compartments do not commonly serve as an inoculum for the subsequent high-pressure membranes. Besides bacteria also fungi are detected in the water treatment compartments. In contrast to bacteria, the fungal community does not change much throughout membrane cleaning. The stable fungal diversity indicates that they are more significant in membrane biofouling than previously thought. By reviewing the biodiversity and ecology of microbes in the whole high pressure membrane filtration water chain, we have been able to identify potentials to improve biofouling control. These include modulation of hydrodynamic conditions, nutrient limitation and the combination of cleaning agents to target the entire membrane microbiome.
Topics: Biodiversity; Biofilms; Biofouling; Filtration; Membranes, Artificial; Osmosis; RNA, Ribosomal, 16S; Water Purification
PubMed: 31986400
DOI: 10.1016/j.watres.2020.115511 -
CBE Life Sciences Education 2011Biology student mastery regarding the mechanisms of diffusion and osmosis is difficult to achieve. To monitor comprehension of these processes among students at a large...
Biology student mastery regarding the mechanisms of diffusion and osmosis is difficult to achieve. To monitor comprehension of these processes among students at a large public university, we developed and validated an 18-item Osmosis and Diffusion Conceptual Assessment (ODCA). This assessment includes two-tiered items, some adopted or modified from the previously published Diffusion and Osmosis Diagnostic Test (DODT) and some newly developed items. The ODCA, a validated instrument containing fewer items than the DODT and emphasizing different content areas within the realm of osmosis and diffusion, better aligns with our curriculum. Creation of the ODCA involved removal of six DODT item pairs, modification of another six DODT item pairs, and development of three new item pairs addressing basic osmosis and diffusion concepts. Responses to ODCA items testing the same concepts as the DODT were remarkably similar to responses to the DODT collected from students 15 yr earlier, suggesting that student mastery regarding the mechanisms of diffusion and osmosis remains elusive.
Topics: Biology; Comprehension; Diffusion; Educational Measurement; Educational Technology; Humans; Osmosis; Program Evaluation; Students; Surveys and Questionnaires
PubMed: 22135375
DOI: 10.1187/cbe.11-04-0038 -
Physiological Research 2000A mathematical description is presented of osmotic flows across both ideally semipermeable membranes and membranes permeable not only for the solvent but also for the... (Review)
Review
A mathematical description is presented of osmotic flows across both ideally semipermeable membranes and membranes permeable not only for the solvent but also for the solute. The principles of thermodynamics of irreversible processes used for the description are given and illustrated on the example of electroosmosis. Modern ideas about the physical basis of osmotic pressure on porous membranes are discussed and an experiment is described that models the processes of osmosis on a macroscopic level.
Topics: Membranes; Models, Biological; Osmosis; Osmotic Pressure; Permeability; Thermodynamics
PubMed: 10984083
DOI: No ID Found -
The Journal of Physiology Mar 19661. The relation between osmotic gradient and rate of osmotic water flow has been measured in rabbit gall-bladder by a gravimetric procedure and by a rapid method based...
1. The relation between osmotic gradient and rate of osmotic water flow has been measured in rabbit gall-bladder by a gravimetric procedure and by a rapid method based on streaming potentials. Streaming potentials were directly proportional to gravimetrically measured water fluxes.2. As in many other tissues, water flow was found to vary with gradient in a markedly non-linear fashion. There was no consistent relation between the water permeability and either the direction or the rate of water flow.3. Water flow in response to a given gradient decreased at higher osmolarities. The resistance to water flow increased linearly with osmolarity over the range 186-825 m-osM.4. The resistance to water flow was the same when the gall-bladder separated any two bathing solutions with the same average osmolarity, regardless of the magnitude of the gradient. In other words, the rate of water flow is given by the expression (O(m) - O(s))/[R(o)' + (1/2)k' (O(m) + O(s))], where R(o)' and k' are constants and O(m) and O(s) are the bathing solution osmolarities.5. Of the theories advanced to explain non-linear osmosis in other tissues, flow-induced membrane deformations, unstirred layers, asymmetrical series-membrane effects, and non-osmotic effects of solutes could not explain the results. However, experimental measurements of water permeability as a function of osmolarity permitted quantitative reconstruction of the observed water flow-osmotic gradient curves. Hence non-linear osmosis in rabbit gall-bladder is due to a decrease in water permeability with increasing osmolarity.6. The results suggest that aqueous channels in the cell membrane behave as osmometers, shrinking in concentrated solutions of impermeant molecules and thereby increasing membrane resistance to water flow. A mathematical formulation of such a membrane structure is offered.
Topics: Animals; Cell Membrane Permeability; Electrophysiology; Gallbladder; In Vitro Techniques; Osmosis; Rabbits; Sucrose
PubMed: 5945254
DOI: 10.1113/jphysiol.1966.sp007851 -
Transactions of the American Clinical... 2012As a major component of homeostasis, all organisms regulate the water composition of various compartments. Through the selective use of barrier membranes and surface... (Review)
Review
As a major component of homeostasis, all organisms regulate the water composition of various compartments. Through the selective use of barrier membranes and surface glycoproteins, as well as aquaporin water channels, organisms ranging from Archaebacteria to humans can vary water permeabilities across their cell membranes by 4 to 5 orders of magnitude. In barrier epithelia the outer, or exofacial, leaflet acts as the main resistor to water flow; this leaflet restricts water flow by minimizing the surface area of lipid molecules which is not covered by phosphate headgroups and by packing hydrocarbon chains at maximal density. Cells may enhance the barrier by expressing glycoproteins that augment the "thickness" of unstirred layers at their surfaces, reducing osmotic gradients at the lipid bilayer surface. Aquaporins markedly and highly selectively accelerate water flux and are "switched on" either by deployment into membranes or gating. This review summarizes these mechanisms in many species, and indicates potential roles for manipulating water permeabilities in treating disease.
Topics: Animals; Aquaporins; Biological Evolution; Biological Transport; Cell Membrane Permeability; Homeostasis; Humans; Lipid Bilayers; Osmosis; Water
PubMed: 23303973
DOI: No ID Found -
Giornale Italiano Di Nefrologia :... Feb 2016Less is generally known about the ideas, events and personalities which drove developments permitting the evolution of haemodialysis as a clinically useful form of...
Less is generally known about the ideas, events and personalities which drove developments permitting the evolution of haemodialysis as a clinically useful form of palliation and treatment, than its subsequent success and failures. This pre-history of haemodialysis is summarized here. One must remember that with hindsight we can now discern connections between ideas and developments which were not perceptible in their time, and that progress towards any new idea, material or piece of hardware was usually random and undirected, and outcomes uncertain. We must also remember the many blind alleys we can now safely ignore, to give a spurious continuity to the development of ideas. The prehistory of dialysis begins with study of the diffusion of solute and solvent in osmosis in living systems and experimental settings, and the retention of potentially toxic substances in kidney failure, during the 18th and early 19th centuries. These two areas came together in work in the mid-19th century on diffusion of gases and liquids, and showed that natural and synthetic membranes could selectively hinder different solutes. This explained osmosis and allowed semi-permeable membranes to be used and designed. These ideas underpinned the subsequent history of both dialysis using body cavities such as the peritoneum (not discussed here) and ex vivo dialysis of blood. To perform this, new membranes and anticoagulants were needed. These led to the first attempts in animals in 1912-3, and human patients in 1924-8, but only the purification and synthesis of newer materials such as cellulose and heparin allowed practical and successful haemodialysis to evolve in the 1940s.
Topics: Animals; History, 18th Century; History, 19th Century; History, 20th Century; Humans; Osmosis; Renal Dialysis; Uremia
PubMed: 26913871
DOI: No ID Found -
Nature Communications Sep 2023Members of the NETWORKED (NET) family are involved in actin-membrane interactions. Here we show that two members of the NET family, NET4A and NET4B, are essential for...
Members of the NETWORKED (NET) family are involved in actin-membrane interactions. Here we show that two members of the NET family, NET4A and NET4B, are essential for normal guard cell actin reorganization, which is a process critical for stomatal closure in plant immunity. NET4 proteins interact with F-actin and with members of the Rab7 GTPase RABG3 family through two distinct domains, allowing for simultaneous localization to actin filaments and the tonoplast. NET4 proteins interact with GTP-bound, active RABG3 members, suggesting their function being downstream effectors. We also show that RABG3b is critical for stomatal closure induced by microbial patterns. Taken together, we conclude that the actin cytoskeletal remodelling during stomatal closure involves a molecular link between actin filaments and the tonoplast, which is mediated by the NET4-RABG3b interaction. We propose that stomatal closure to microbial patterns involves the coordinated action of immune-triggered osmotic changes and actin cytoskeletal remodelling likely driving compact vacuolar morphologies.
Topics: Actins; Vacuoles; Actin Cytoskeleton; Cell Physiological Phenomena; Osmosis
PubMed: 37730720
DOI: 10.1038/s41467-023-41337-z -
Journal of Dairy Science Jul 2021Concentration of milk in the dairy industry is typically achieved by thermal evaporation or reverse osmosis (RO). Heat concentration is energy intensive and leads to...
Concentration of milk in the dairy industry is typically achieved by thermal evaporation or reverse osmosis (RO). Heat concentration is energy intensive and leads to cooked flavor and color changes in the final product, and RO is affected by fouling, which limits the final achievable concentration of the product. The main objective of this work was to evaluate forward osmosis (FO) as an alternative method for concentrating milk. The effects of fat content and temperature on the process were evaluated, and the physicochemical properties and sensory qualities of the final product were assessed. Commercially pasteurized skim and whole milk samples were concentrated at 4, 15, and 25°C using a benchtop FO unit. The FO process was assessed by monitoring water flux and product concentration. The color of the milk concentrates was also evaluated. A sensory panel compared the FO concentrated and thermally concentrated milks, diluted to single strength, with high temperature, short time pasteurized milk. The FO experimental runs were conducted in triplicate, and data were analyzed by single-factor ANOVA. Water flux during FO decreased with time under all processing conditions. Higher temperatures led to faster concentration and higher concentration factors for both skim and whole milk. After 5.75 h of FO processing, the concentration factors achieved for skim milk were 2.68 ± 0.08 at 25°C, 2.68 ± 0.09 at 15°C, and 2.36 ± 0.08 at 4°C. For whole milk, after 5.75 h of FO processing, concentration factors of 2.32 ± 0.12 at 25°C, 2.12 ± 0.36 at 15°C, and 1.91 ± 0.15 at 4°C were obtained. Overall, maximum concentration levels of 40.15% total solids for skim milk and 40.94% total solids for whole milk were achieved. Additionally, a triangle sensory test showed no significant differences between regular milk and FO concentrated milk diluted to single strength. This work shows that FO is a viable nonthermal processing method for concentrating milk, but some technical challenges need to be overcome to facilitate commercial utilization.
Topics: Animals; Filtration; Flavoring Agents; Membranes, Artificial; Milk; Osmosis; Taste
PubMed: 33865601
DOI: 10.3168/jds.2020-20019 -
JASA Express Letters Aug 2021Electro-osmosis (EO) is a non-traditional pumping and transduction mechanism with the ability to project acoustic energy in fluids. This investigation experimentally...
Electro-osmosis (EO) is a non-traditional pumping and transduction mechanism with the ability to project acoustic energy in fluids. This investigation experimentally validates the influence of zeta potential, a well-studied physical characteristic used for quantifying the efficacy of an EO pump, on generation of sound pressure level. Acoustic signals of discrete frequencies were observed from 130 Hz to over 150 kHz. EO-type projectors are an attractive technology in that it does not contain moving parts, can be fabricated using a variety of materials, is intrinsically resilient to effects of hydrostatic pressure, and may be designed on the micro-electromechanical system scale.
Topics: Acoustics; Osmosis
PubMed: 36154251
DOI: 10.1121/10.0005763