Osmotic Research Articles

Sink Strength During Sugarcane Culm Growth: Size Matters

Sugarcane growth and its subsequent yield are linked to plant height. The increase in sugarcane height is controlled by elongation of the top 6 to 7 internodes. The elongation of the internodes can be significantly reduced by an application of the Trinexapac-ethyl (Moddus®) which is a known disruptor of GA synthesis. In this study, the growth and composition of the internodes were analysed following the treatment. We found that the strong inhibitory effect of Moddus® on internode size was due to a strongly suppressed rate of internode elongation, with no effect on the duration of the elongation period. The Moddus® inhibition of internode elongation was not due to a lack of an osmotic potential gradient but probably reflects a higher pressure potential of the tissue. A consequence of the reduced internode size was a significant reduction in carbon flow (sink strength) of the internode. It was not only the rate of internode growth that was altered by Moddus®, but also partitioning within the internode. Partitioning of carbon into components other than the soluble sugars and cell wall was significantly reduced by the Moddus® treatment. The high reducing sugar content in the Moddus® treatment suggests that sucrose mobilisation (hydrolysis by invertases and cleavage by sucrose synthase) might, like the duration of elongation, be controlled by thermal time. No accumulation of reducing sugars was evident in the control internodes probably due to the rapid mobilisation to other cellular processes. Sucrose accumulation in the internode reflected a cessation of sugar utilisation to support growth and maintenance.

Forward Osmosis for Metal Processing Effluents under Similar Osmotic Pressure Gradients.

Water recovery from aqueous effluents in the mining and metals processing industry poses a unique challenge due to the high concentration of dissolved salts typically requiring energy intensive methods of treatment. Forward osmosis (FO) is a lower energy technology which employs a draw solution to osmotically extract water through a semi-permeable membrane further concentrating any feed. Successful FO operation relies on using a draw solution of higher osmotic pressure than the feed to extract water while minimizing concentration polarization to maximize the water flux. Previous studies employing FO on industrial feed samples commonly used concentration instead of osmotic pressures for feed and draw characterization; this led to misleading conclusions on the impact of design variables on water flux performance. By employing a factorial design of experiments methodology, this study examined the independent and interactive effects on water flux by: osmotic pressure gradient, crossflow velocity, draw salt type, and membrane orientation. With a commercial FO membrane, this work tested a solvent extraction raffinate and a mine water effluent sample to demonstrate application significance. By optimizing with osmotic gradient independent variables, water flux can be improved by over 30% without increasing energy costs or compromising the 95-99% salt rejection of the membrane.

Hyperosmolar therapy for regulation of cerebral edema and intracranial pressure

Background: Hyperosmolar therapy is an essential treatment method for increased intracranial pressure and cerebral edema. Mannitol and hypertonic saline are frequently used in clinical practice; however, more helpful recommendations are needed for the optimal management of cerebral edema in terms of the choice, dosage, and timing of these medications. This study aimed to introduce the characteristics and relative strengths of two agents, i.e., mannitol and hypertonic saline, and review clinical data supporting their use in various diseases.Current Concepts: Hyperosmolar therapy reduces intracranial pressure by removing water from the brain tissue and transferring it to the vascular space by creating an osmotic gradient. Mannitol improves cerebral blood flow by reducing the hematocrit, decreasing blood viscosity, and increasing deformability of red blood cells. Hypertonic saline increases intravascular volume, transiently increases cardiac output, and improves tissue oxygen partial pressure in the brain. Hypertonic saline has several advantages over mannitol, including quicker onset and longer-lasting reduction in intracranial pressure. However, no significant differences are noted in clinical, functional outcomes, or mortality between the two treatment agents.Discussion and Conclusion: Both mannitol and hypertonic saline are effective in reducing increased intracranial pressure. Clinicians should be able to select an appropriate agent in different clinical situations based on available evidence and patients’ individual medical conditions.

Drugging aquaporins

Water is essential for all life because it is required for the proper functioning of the cells and tissues of all organisms. It crosses biological membranes down osmotic gradients through the pores of aquaporin membrane channels at rates of up to 3 billion molecules per second. In the twenty years since Peter Agre was awarded the 2003 Nobel Prize in Chemistry for the discovery of the aquaporin family, aquaporin structure and function have become established in the literature. As a consequence, we understand in fine detail the mechanism by which aquaporins facilitate membrane water flow while excluding protons. We also know that some aquaporins facilitate the permeation of other small neutral solutes, ions or even unexpected substrates across biological membranes. The thirteen aquaporins in the human body have been implicated in pathologies including oedema, epilepsy, cancer cell migration, tumour angiogenesis, metabolic disorders and inflammation. Surprisingly, however, there is no aquaporin-targeted drug in the clinic. Some scientists have therefore concluded that aquaporins are intrinsically non-druggable targets. Discovering medicines to treat disorders of water homeostasis is thus an enduring challenge for the aquaporin field. Success in this endeavour will meet the urgent clinical need of millions of patients suffering from a range of life-threatening conditions and for whom no pharmacological interventions are currently available.

Blockade of sodium-glucose co-transporters improves peritoneal ultrafiltration in uraemic rodent models.

The most used PD fluids contain glucose as a primary osmotic agent. Glucose peritoneal absorption during dwell decreases the osmotic gradient of peritoneal fluids and causes undesirable metabolic consequences. Inhibitors of sodium-glucose co-transporter (SGLT) type 2 are wildly used for the treatment of diabetes, heart and kidney failure. Previous attempts to use SGLT2 blockers in experimental peritoneal dialysis yielded contrasting results. We studied whether peritoneal SGLTs blockade may improve ultrafiltration (UF) via partial inhibition of glucose uptake from dialysis fluids. Kidney failure was induced in mice and rats by bilateral ureteral ligation, and dwell was performed by injection of glucose-containing dialysis fluids. The effect of SGLT inhibitors on glucose absorption during fluid dwell and UF was measured in vivo. Diffusion of glucose from dialysis fluid into the blood appeared to be sodium-dependent, and blockade of SGLTs by phlorizin and sotagliflozin attenuated blood glucose increment thereby decreasing fluid absorption. Specific SGLT2 inhibitors failed to reduce glucose and fluid absorption from the peritoneal cavity in a rodent kidney failure model. Our study suggests that peritoneal non-type 2 SGLTs facilitate glucose diffusion from dialysis solutions, and we propose that limiting glucose reabsorption by specific SGLT inhibitors may emerge as a novel strategy in PD treatment to enhance UF and mitigate the deleterious effects of hyperglycaemia.

How to Study Osmosis If the Membrane Water Moves Across Is Nonideal

In our past works, we introduced two fundamental osmosis systems (a simple S-m-H 2 O and a composite S 1 -m-S 2 ) to study osmosis 1,2 , where m is a selectively permeable membrane that separates two fluid compartments. A composite S 1 -m-S 2 can be deconstructed into two simple osmosis systems (S 1 -m-H 2 O and H 2 O-m-S 2 ) 1,2 . When applying these two fundamental osmosis systems, a given m can either be permeable to water only (an ideal m) or its permeability to one species of non-charged solute particles (SP, e.g., urea) can be ignored. If m' represents a nonideal membrane whose permeability to urea cannot be ignored, then a new research question emerges: how can osmosis be studied in S-m'-H 2 O and S 1 -m'-S 2 , respectively? This abstract provides the answers by logical reasoning. First, S-m'-H 2 O can be viewed as the overlap of a pure osmosis system with an ideal m (S-m-H 2 O) and a permeant SP (pSP), urea diffusion system: S-m'-H 2 O = S-m-H 2 O + S urea -m'-H 2 O, so that osmosis and urea diffusion can be studied separately. The former is governed by van ’t Hoff’s law and the latter by Fick’s law. Second, similarly, S 1 -m'-S 2 = S 1 -m-S 2 + S 1urea -m'-S 2urea . Third, the effect of urea diffusion on osmosis depends on several conditions: 1) In S-m'-H 2 O, urea diffusion and osmosis are always in opposite directions, so urea diffusion reduces the resulting osmotic pressure (π). 2) In S 1 -m'-S 2 , if S 1 is hypertonic to S 2 and [urea] S1 > [urea] S2 , then the diffusion and osmosis are in opposite directions, so the diffusion reduces the resulting osmotic pressure gradient (Δ π). 3) If S 1 is hypotonic to S 2 and [urea] S1 > [urea] S2 , then osmosis and diffusion are in the same direction, so the diffusion augments the resulting Δ π. In conclusion: 1) Deconstruction of an osmosis system that has a nonideal m' allows separate studies of osmosis and pSP diffusion, respectively. 2) The effect of pSP diffusion on osmosis needs to be differentiated according to the type of osmosis systems and the direction of osmosis and pSP diffusion. 3) While the simple S-m-H 2 O and composite S 1 -m-S 2 are fundamental osmosis systems, S-m'-H 2 O and S 1 -m'-S 2 are complex passive membrane transport systems that transport both water and pSP. 4) If a given nonideal m' is permeable to two types of pSP (e.g., urea and glucose), then the diffusion system needs to be further deconstructed into a urea diffusion system and a glucose diffusion system.

The Nature and Properties of Tonicity

We proposed that tonicity has a physical nature and three properties 1 . In this abstract, we prove this hypothesis to be true by logical reasoning. Two key terms will be used: 1) S 1 -m-S 2 (a composite osmosis system that can be deconstructed into two simple osmosis systems: S 1 -m-H 2 O and H 2 O-m-S 2 1 ; and 2) OC 0 , the initial osmotic concentration (concentration of the impermeant solute particles (impSP)) before osmosis occurs (time = 0) 2 . Results are as follows. 1) Since we defined tonicity to be a relational concept that reflects a comparison of two OC 0 in S 1 -m-S 2 1 , if OC 0 (S 1 ) = 90 mOsm/L and OC 0 (S 2 )= 30 mOsm/L, then Δ OC0 (S 1 -S 2 ) = 90 – 30 = 60 mOsm/L, which contributes to the force that drives osmosis and an osmotic pressure gradient (Δ π) results 3 . Δ OC 0 informs the tonicity (i.e., S 1 is hypertonic to S 2 ) directly and Δ π indirectly, so both can be used to express tonicity (the comparison) 4 . Either Δ OC 0 or Δ π is a form of energy, thus tonicity has a physical nature. Tonicity is often inappropriately described as a solution's ability to change a cell’s volume 5 . As shown in this work, it is Δ OC 0 (S 1 -S 2 ) that has the ability to cause a change in cell volume, not any single solution in S 1 ‐m‐S 2 . 2) The first property of tonicity is m-dependent: Facing different m, different fractions of the impSP result, so OC 0 is m-dependent 2 ; tonicity compares two OC 0 separated by a given m, thus is m-dependent too. 3) The second property is relativity (reference-solution dependency: S 2 in S 1 -m-S 2 can be replaced by S X (X = 1, 2, 3, …n), a reference solution for S 1 . In contrast, in any simple osmosis system (S-m-H 2 O) 1 , the reference solution for S is always water with 0 mOsm/L, which cannot be replaced by any solution. 4) The third property is reciprocity because the same comparison can be described as either “S 1 is hypertonic to S 2 or S 2 is hypotonic to S 1 ” or “ Δ OC 0 (S 1 -S 2 ) or Δ OC 0 (S 2 –S 1 )” etc. Hence, we conclude: Tonicity can be expressed using either Δ OC 0 or Δ π. Either stores a form of energy representing a physical nature. OC 0 (defined in a simple S-m-H 2 O) and tonicity (defined in a composite S 1 -m-S 2 ) are both m-dependent, whereas relativity and reciprocity are properties of tonicity only.

Aberrant adaptation of the inner medullary collecting ducts results in sodium retention and hypernatremia in a thick ascending limb specific Myh9 and Myh10 conditional knockout mouse model

Sodium reabsorption in the thick ascending limb (TAL) epithelium is essential to generate and sustain the interstitial osmotic gradient, which facilitates water reabsorption in the adjacent collecting duct system. Impaired TAL function can compromise this gradient and lead to electrolyte imbalance. Our previous work demonstrated that pan renal tubular conditional genetic inactivation of nonmuscle myosin II genes Myh9&10 in adult mice results in progressive kidney disease of TAL origin with aberrant regulation of TAL proteins U MOD and NKCC2 (Otterpohl et al; 2020). To confirm the cell-autonomous role for NM2 proteins in adult TAL epithelial cells, we generated a TAL-specific conditional knockout mouse model of Myh9&10 using the UMOD->CreERT2 mouse line (cKO). Genetic inactivation of Myh9&10 in the TAL was induced at 5 weeks of age with tamoxifen injections. Age matched control and cKO littermates were part of every cohort. Mice underwent metabolic, histologic, immunohistochemical, and biochemical analyses at varying time points until moribund. Development of progressive kidney disease in cKO mice was indicated by increasing levels of blood urea nitrogen, serum creatinine, and the tubular injury marker NGAL. Our results show that cKO females experience significant loss of weight at 12 weeks of age and are moribund between 13 – 14 weeks, while cKO males survive up to 25 weeks. Interestingly, female cKO mice exhibit hypernatremia at 12 weeks of age and male cKO mice between 16 - 20 weeks of age. We analyzed NKCC2 protein levels in whole kidney lysates and a drastic reduction was evident in both female and male cKO mice by 9 weeks of age, therefore hypernatremia was unexpected. We examined if the hypernatremia in TAL-Myh9&10 cKO mice is due to tubular adaptation in the distal nephron and/or the collecting duct segments. Systematic analysis of sodium cotransporters and channels in the distal nephron and collecting duct segments revealed an increase in NCC/pNCC levels in males and a decrease in females when compared with age matched control littermates. No apparent volume loss (increased urine output) has been observed in the female mice. Additionally, immunostaining experiments showed aberrant increase in expression of ENaC gamma in the inner medullary collecting duct cells in female and not male mice by 9-weeks of age. ENaC expression is limited to cortical collecting duct and the connecting segment under normal conditions in the mouse kidney. Consistent with this, our control mice do not have ENaC gamma expression in the inner medullary collecting ducts. Further experiments are underway to determine the cellular state/identity of these ENaC expressing inner medullary collect duct cells. These experiments confirm the critical role for Myh9&10 proteins in TAL tubule NKCC2 transport, and reveal novel, sex specific, adaptive mechanisms in distal nephron and collecting ducts in response to compromised NKCC2 transport within the TAL. NIDDK RO1 DK131020-01A1 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

TRANSFERSOMES AS NOVEL DRUG DELIVERY SYSTEM

Transdermal drug delivery appears to be most vital drug delivery system because of its merit over conventional systems. Transferosomes & the fundamental concept of transfersomes were launched by Gregor Cevc in the year 1991. The name means carrying body and is derived from the Latin word transferre, meaning to carry across and the Greek word soma, meaning a body. Novel drug delivery system aims to deliver the drug at a rate directed by need of body during the period of treatment and channel the active entity to the site of action. Transferosome is one of the novel vesicular drug delivery system which consists of phospholipids, surfactant and water for enhanced transdermal delivery. Transferosomes are able to reach intact deeper regions of the skin after topical drug administration while delivering higher concentrations of active substances making them a successful carrier for transdermal applications. These vesicular systems can deliver low as well as high molecular weight compounds. Targeted and controlled release formulations can also be prepared by transferosomes as it can accommodate drug molecules with wide range of solubility. Various strategies can be used to augment the transdermal delivery which includes iontophoresis, electrophoresis, sonophoresis, chemical permeation enhancers, microneedles, & vesicular system (liposomes, niosomes, elastic liposomes such as ethosomes & transfersomes). It exists as an ultra-deformable complex having a hydrated core surrounded by a complex layer of lipid. It penetrates the stratum corneum by either intracellular route or the transcellular route by the generation of osmotic gradient. Advantages of Transferosomes are wide range of solubilities, better penetration, biocompatible and biodegradable etc. Disadvantages of Transferosomes are oxidative degradation, expensive, etc. The transfersomes were formulated by the conventional rotary evaporation sonication method. Transferosomes can be applied in controlled release, transportation of large molecular weight compounds, target delivery to peripheral subcutaneous tissues, transdermal immunization etc.

Expert Consensus on the Use of Human Serum Albumin in Adult Cardiac Surgery.

Expert Consensus on the Use of Human Serum Albumin in Adult Cardiac Surgery.

Biodegradable Preformed Particle Gel (PPG) Made of Natural Chitosan Material for Water Shut-Off Application.

Oil and gas extraction frequently produces substantial volumes of produced water, leading to several mechanical and environmental issues. Several methods have been applied over decades, including chemical processes such as in-situ crosslinked polymer gel and preformed particle gel, which are the most effective nowadays. This study developed a green and biodegradable PPG made of PAM and chitosan as a blocking agent for water shutoff, which will contribute to combating the toxicity of several commercially used PPGs. The applicability of chitosan to act as a crosslinker has been confirmed by FTIR spectroscopy and observed by scanning electron microscopy. Extensive swelling capacity measurements and rheological experiments were performed to examine the optimal formulation of PAM/Cs based on several PAM and chitosan concentrations and the effects of typical reservoir conditions, such as salinity, temperature, and pH. The optimum concentrations of PAM with 0.5 wt% chitosan were between 5-9 wt%, while the optimum chitosan amount with 6.5 wt% PAM was in the 0.25-0.5 wt% range, as these concentrations can produce PPGs with high swellability and sufficient strength. The swelling capacity of PAM/Cs is lower in high saline water (HSW) with a TDS of 67.2976 g/L compared with fresh water, which is related to the osmotic pressure gradient between the swelling medium and the PPG. The swelling capacity in freshwater was up to 80.37 g/g, while it is 18.73 g/g in HSW. The storage moduli were higher in HSW than freshwater, with ranges of 1695-5000 Pa and 2053-5989 Pa, respectively. The storage modulus of PAM/Cs samples was higher in a neutral medium (pH = 6), where the fluctuation behavior in different pH conditions is related to electrostatic repulsions and hydrogen bond formation. The increase in swelling capacity caused by the progressive increment in temperature is associated with the amide group's hydrolysis to carboxylate groups. The sizes of the swollen particles are controllable since they are designed to be 0.63-1.62 mm in DIW and 0.86-1.00 mm in HSW. PAM/Cs showed promising swelling and rheological characteristics while demonstrating long-term thermal and hydrolytic stability in high-temperature and high-salinity conditions.

Seasonal changes in blood rheology in little ground squirrels.

The annual cycle of small ground squirrels (Spermophilus pygmaeus) consists of 2 periods: wakefulness (spring-autumn) and hibernation (winter). During the active period, ground squirrels breed (spring), accumulate fat reserves (summer) and prepare for hibernation (autumn). We suppose that the rheological properties of blood and the deformability of erythrocytes can change in different seasons of the animal's wakefulness period to adequately provide tissues with oxygen. The aim of this study was to identify possible adaptive changes in erythrocyte deformability and erythrocyte indices in ground squirrels during their active period. The deformability of erythrocytes was studied by ektacytometry in an osmotic gradient. It was found that in spring, after the arousal of ground squirrels, erythrocytes have the highest deformability (El_max), hydration (O_hyper), water permeability (El_min) and osmotic stability (∆O). In summer, compared with spring, the deformability of erythrocytes decreases, and the average volume of erythrocytes (MCV) also decreases. In autumn, before hibernation, the integral deformability of erythrocytes, their hydration, as well as the range of osmotic stability of erythrocytes increases relative to the summer period. In summer and autumn, in contrast to spring, the average concentration of hemoglobin in the erythrocyte (MCHC) increases. At low shear stress (1 Pa) in summer and autumn, osmoscan becomes a pronounced polymodal form, indicating a change in the viscoelastic properties of ground squirrel erythrocyte membranes. Thus, for the first time, we discovered seasonal variability in the deformability of ground squirrel erythrocytes, which is consistent with the spring-summer activity of animals and preparation for hibernation.

An evaluation of different pretreatment methods of hot-air drying of garlic: Drying characteristics, energy consumption and quality properties

Various drying pretreatment techniques play an important role in the drying process. This study investigated the effect of ultrasound (US), osmosis (OM) and freeze-thaw (FT) pretreatments on the hot-air drying characteristics, physical characteristics, rehydration characteristics, and allicin content of garlic. The results showed that the application of different pretreatments increased the drying efficiency and reduced the total energy consumption, compared with unpretreated garlic. Particularly, drying garlic with US pretreatment reduced the drying time by 450, 270 and 90 min and the total energy consumption was 24.45%, 20.60% and 18.09% less at 50, 60 and 70 °C, respectively. These improvements attribute to an increasement in porous structure by US, which leads to an increase in water diffusion capacity. Moreover, US drying had lowest color difference, highest rehydration rate and allicin content. The Midilli model could satisfactorily describe the drying curves of US pretreated garlic.

Are standing osmotic gradients the main driver of cerebrospinal fluid production? A computational analysis

BackgroundThe mechanisms of cerebrospinal fluid (CSF) production by the ventricular choroid plexus (ChP) have not been fully deciphered. One prominent hypothesized mechanism is trans-epithelial water transport mediated by accumulation of solutes at the luminal ChP membrane that produces local osmotic gradients. However, this standing osmotic gradient hypothesis has not been systematically tested.MethodsTo assess the plausibility of the standing gradient mechanism serving as the main driver of CSF production by the ChP, we developed a three-dimensional (3D) and a one-dimensional (1D) computational model to quantitatively describe the associated processes in the rat ChP inter-microvillar spaces and in CSF pools between macroscopic ChP folds (1D only). The computationally expensive 3D model was used to examine the applicability of the 1D model for hypothesis testing. The 1D model was employed to predict the rate of CSF produced by the standing gradient mechanism for 200,000 parameter permutations. Model parameter values for each permutation were chosen by random sampling from distributions derived from published experimental data.ResultsBoth models predict that the CSF production rate by the standing osmotic gradient mechanism is below 10% of experimentally measured values that reflect the contribution of all actual production mechanisms. The 1D model indicates that increasing the size of CSF pools between ChP folds, where diffusion dominates solute transport, would increase the contribution of the standing gradient mechanism to CSF production.ConclusionsThe models suggest that the effect of standing osmotic gradients is too small to contribute substantially to CSF production. ChP motion and movement of CSF in the ventricles, which are not accounted for in the models, would further reduce this effect, making it unlikely that standing osmotic gradients are the main drivers of CSF production.

The Vagus Nerve Mediates Gut-Brain Response to Duodenal Nutrient Administration.

Obesity contributes significant disease burden worldwide, including diabetes, cardiovascular disease, and cancer. While bariatric surgery is the most effective and durable obesity treatment, the mechanisms underlying its effects remain unknown. Although neuro-hormonal mechanisms have been suspected to mediate at least some of the gut-brain axis changes following bariatric surgery, studies examining the intestine and its regionally specific post-gastric alterations to these signals remain unclear. Vagus nerve recording was performed following the implantation of duodenal feeding tubes in mice. Testing conditions and measurements were made under anesthesia during baseline, nutrient or vehicle solution delivery, and post-delivery. Solutions tested included water, glucose, glucose with an inhibitor of glucose absorption (phlorizin), and a hydrolyzed protein solution. Vagus nerve signaling was detectable from the duodenum and exhibited stable baseline activity without responding to osmotic pressure gradients. Duodenal-delivered glucose and protein robustly increased vagus nerve signaling, but increased signaling was abolished during the co-administration of glucose and phlorizin. Gut-brain communication via the vagus nerve emanating from the duodenum is nutrient sensitive and easily measurable in mice. Examination of these signaling pathways may help elucidate how the nutrient signals from the intestine are altered when applied to obesity and bariatric surgery mouse models. Future studies will address quantifying the changes in neuroendocrine nutrient signals in health and obesity, with specific emphasis on identifying the changes associated with bariatric surgery and other gastrointestinal surgery.

CAN POLYETHYLENE GLYCOL-20K REPLACE ALBUMIN FOR PREHOSPITAL TREATMENT OF HEMORRHAGIC SHOCK WHEN FULL RESUSCITATION IS UNAVAILABLE?

A solution of high concentration albumin has been used for temporal volume expansion when timely resuscitation was unavailable after hemorrhagic shock. However, during prolonged hemorrhagic shock, cell edema and interstitial dehydration can occur and impede the volume expansion effect of albumin. Polyethylene glycol-20K (PEG) can establish an osmotic gradient from swollen cells to capillary lumens and thus facilitate capillary fluid shift and volume expansion. We hypothesized that with similar osmolality, 7.5% PEG elicits more rapid and profound compensatory responses after hemorrhagic shock than 25% albumin. Rats were randomized into three groups (n = 8/group) based on treatment: saline (vehicle), PEG (7.5%), and albumin (25%). Trauma was induced in anesthetized rats with muscle injury and fibula fracture, followed by pressure-controlled hemorrhagic shock (MAP = 55 mm Hg) for 45 min. Animals then received an intravenous injection (0.3 mL/kg) of saline, PEG, or albumin. MAP, heart rate, blood gases, hematocrit, skeletal muscle capillary flow, renal blood flow, glomerular filtration rate, urinary flow, urinary sodium concentration, and mortality were monitored for another 2 hours. Polyethylene glycol-20K and albumin both improved MAP, renal and capillary blood flow, and renal oxygen delivery, and decreased hyperkalemia, hyperlactatemia, hematocrit, and mortality (saline: 100% PEG: 12.5%; albumin: 38%) over saline treatment. Compared with albumin, PEG had a more rapid decrease in hematocrit and more profound increases in MAP, diastolic pressure, renal blood flow, glomerular filtration rate, and urinary flow. These results suggest that PEG may be a better option than albumin for prolonged prehospital care of hemorrhagic shock.

New-Generation Ektacytometry Study of Red Blood Cells in Different Hemoglobinopathies and Thalassemia

Next-generation ektacytometry provided by the osmoscan module of the Laser Optical Rotational Red Cell Analyser (LoRRca) MaxSis is, so far, one of the best complementary diagnostic tools for congenital rare anaemias due to red blood cell defects. Osmotic gradient ektacytometry (OGE) is currently considered the gold standard for the diagnosis of red cell membrane disorders, especially hereditary spherocytosis (HS). Impairment of red cell deformability, leading to a decrease in red cell survival rate, is the common trait of hereditary haemolytic anaemias; in general, it is the consequence of an abnormal cell shape, increased rigidity or dehydration. Up to now, the next-generation ektacytometry has been mainly used for the differential diagnosis of red blood cell membranopathies, but experience with structural hemoglobinopathies and thalassemia is still scarce. However, recently, many new forms of therapy are being developed for the treatment of hemoglobinopathies, particularly sickle-cell disease and β-thalassemia; clinical interest in ektacytometry is increasing and should be further explored. Here, we have evaluated the OGE profiles provided by the osmoscan module of the LoRRca ektacytometer in 96 patients with different hemoglobinopathies, both structural and thalassemia, with the aim of analysing their usefulness for the early diagnosis of these disorders either individually or in co-inheritance with other hereditary RBC defects. In addition, this study aims to improve our knowledge of the contribution of red cell deformability, osmotic fragility and intracellular viscosity to the physiopathology of haemolysis, especially when these disorders are a cause of rare anaemia. From this study, we conclude that the osmoscan profile provides complementary information on red cell deformability and hydration homeostasis that may contribute to the better understanding of the physiopathology of decreased red cell survival and hemolysis which is present in some patients.

Neutral polymers partial exclusion in ionic solutions near charged membranes.

Neutral polymers have become a useful tool in biophysics. They are currently used in a variety of single-channel conductance measurements, to change solution conductivity and viscosity, to induce osmotic stress in polymer-excluded regions, or simply as crowding agents. Many experiments involve the proximity of neutral polymers to charged membranes or their confinement in aqueous pores formed by protein channels with charged residues. A well-known phenomenon relevant to this problem is the polarization of a neutral particle with dielectric properties different from the surrounding medium under the effect of an electric field. This polarization causes a dielectrophoretic force when inhomogeneous electric fields act on the particle and it has been extensively used in many biomedical applications involving particle trapping and cell separation, among others. In addition, whenever a neutral particle perturbs the equilibrium electric double layer near a charged surface, the osmotic pressure gradient acts as a net repulsive force that pushes the particle away from that surface. Both the dielectrophoretic force and the hydrostatic force contribute to exclude a neutral particle from a charged surface, provided the polarizability is lower in the particle than in the solution. Here we report analytical predictions and simulations of the exclusion of polyethylene glycol (PEG) molecules of different molecular weight from charged surfaces. Molecular dynamics of PEG near charged DPPS membranes and neutral DPPC membranes show a region of PEG exclusion near the membrane-solution interface for charged membranes. The simulations also point to a preferential alignment of PEG molecules near the charged membrane. The simulations are confirmed by preliminary neutron reflectometry data, which are consistent with an exclusion region of concentrated PEG solutions near the highly charged silicon dioxide/water interface.

Submicron-Sized In Situ Osmotic Pressure Sensors for In Vitro Applications in Biology.

Physical forces are important cues in determining the development and the normal function of biological tissues. While forces generated by molecular motors have been widely studied, forces resulting from osmotic gradients have been less considered in this context. A possible reason is the lack of direct in situ measurement methods that can be applied to cell and organ culture systems. Herein, novel kinds of resonance energy transfer(FRET)-based liposomal sensors are developed, so that their sensing range and sensitivity can be adjusted to satisfy physiological osmotic conditions. Several types of sensors are prepared, either based on polyethylene glycol- (PEG)ylated liposomes with steric stabilization and stealth property or on crosslinked liposomes capable of enduring relatively harsh environments for liposomes (e.g., in the presence of biosurfactants). The sensors are demonstrated to be effective in the measurement of osmotic pressures in pre-osteoblastic in vitro cell culture systems by means of FRET microscopy. This development paves the way toward the in situ sensing of osmotic pressures in biological culture systems.

Convection Confounds Measurements of Osmophoresis for Lipid Vesicles in Solute Gradients.

Lipid vesicles immersed in solute gradients are predicted to migrate from regions of high to low solute concentration due to osmotic flows induced across their semipermeable membranes. This process─known as osmophoresis─is potentially relevant to biological processes such as vesicle trafficking and cell migration; however, there exist significant discrepancies (several orders of magnitude) between experimental observations and theoretical predictions for the vesicle speed. Here, we seek to reconcile predictions of osmophoresis with observations of vesicle motion in osmotic gradients. We prepare quasi-steady solute gradients in a microfluidic chamber using density-matched solutions of sucrose and glucose to eliminate buoyancy-driven flows. We quantify the motions of giant DLPC vesicles and Brownian tracer particles in such gradients using Bayesian analysis of particle tracking data. Despite efforts to mitigate convective flows, we observe directed motion of both lipid vesicles and tracer particles in a common direction at comparable speeds of order 10 nm/s. These observations are not inconsistent with models of osmophoresis, which predict slower motion at ca. 1 nm/s; however, experimental uncertainty and the confounding effects of fluid convection prohibit a quantitative comparison. In contrast to previous reports, we find no evidence for anomalously fast osmophoresis of lipid vesicles when fluid convection is mitigated and quantified. We discuss strategies for enhancing the speed of osmophoresis using high permeability membranes and geometric confinement.