Reduction In Osmotic Pressure Research Articles

Патофизиологические механизмы отека головного мозга при диабетическом кетоацидозе в детской практике

Diabetic ketoacidosis is a frequent complication of type 1 diabetes mellitus in children and adolescents. One of the leading causes of death in this pathology is cerebral edema. This complication is often asymptomatic, which makes it difficult to diagnose. The main risk factors for cerebral edema in children include the true factors (low partial pressure of carbon dioxide, high blood urea nitrogen, concomitant psychiatric pathology, etc.) and iatrogenic factors (large volume of infusion therapy, rapid decrease in blood glucose levels, administration of bicarbonate, etc.). The pathophysiology of this complication is not yet fully understood. The main pathophysiological elements of cerebral edema in children with DKA include the disruption of blood-brain barrier permeability, edema of brain cells, and dysfunction of cell membranes. Important roles are also played by hypercapnia and reduction of osmotic pressure. Based on the character of pathophysiologic changes, cerebral edema in children and adolescents with DKA is subdivided into vasogenic and cytotoxic. Gaining a better understanding of the pathophysiological mechanisms of this complication will increase the quality of care provided in pediatric practice.

Патофизиологические механизмы отека головного мозга при диабетическом кетоацидозе в детской практике

Diabetic ketoacidosis is a frequent complication of type 1 diabetes mellitus in children and adolescents. One of the leading causes of death in this pathology is cerebral edema. This complication is often asymptomatic, which makes it difficult to diagnose. The main risk factors for cerebral edema in children include the true factors (low partial pressure of carbon dioxide, high blood urea nitrogen, concomitant psychiatric pathology, etc.) and iatrogenic factors (large volume of infusion therapy, rapid decrease in blood glucose levels, administration of bicarbonate, etc.). The pathophysiology of this complication is not yet fully understood. The main pathophysiological elements of cerebral edema in children with DKA include the disruption of blood-brain barrier permeability, edema of brain cells, and dysfunction of cell membranes. Important roles are also played by hypercapnia and reduction of osmotic pressure. Based on the character of pathophysiologic changes, cerebral edema in children and adolescents with DKA is subdivided into vasogenic and cytotoxic. Gaining a better understanding of the pathophysiological mechanisms of this complication will increase the quality of care provided in pediatric practice.

Nonmonotonic swelling and compression dynamics of hydrogels in polymer solutions.

Hydrogels are sponge-like materials that can absorb or expel significant amounts of water. Swelling up from a dried state, they can swell up more than a hundredfold in volume, with the kinetics and the degree of swelling depending sensitively on the physicochemical properties of both the polymer network and the aqueous solvent. In particular, the presence of dissolved macromolecules in the background liquid can have a significant effect, as the macromolecules can exert an additional external osmotic pressure on the hydrogel material, thereby reducing the degree of swelling. In this paper, we have submerged dry hydrogel particles in polymer solutions containing large and small macromolecules. Interestingly, for swelling in the presence of large macromolecules we observe a concentration-dependent overshoot behavior, where the particle volume first continuously increases toward a maximum, after which it decreases again, reaching a lower, equilibrium value. In the presence of smaller macromolecules we do not observe this intriguing overshoot behavior, but instead observe a rapid growth followed by a slowed-down growth. To account for the observed overshoot behavior, we realize that the macromolecules entering the hydrogel network not only lead to a reduction of the osmotic pressure difference, but their presence within the network also affects the swelling behavior through a modification of the solvent-polymer interactions. In this physical picture of the swelling process, the net amount of volume change should thus depend on the magnitudes of both the reduction in osmotic pressure and the change in effective solvent quality associated with the macromolecules entering the pores of the hydrogel network. We develop a phenomenological model that incorporates both of these effects. Using this model we are able to account for both the swelling and compression kinetics of hydrogels within aqueous polymer solutions, as a function of the size of the dissolved macromolecules and of their effect on the effective solvent quality.

Effects of treatment agents during acid washing and pH neutralization on the fertility of heavy metal-impacted dredged marine sediment as plant-growing soil

The present study was aimed at investigating the effects of different acids and pH neutralizers applied to dredged marine sediment for the treatment of heavy metals, and the resulting influence on the sediment quality as a plant growth medium. The inspection of barley germination in the dredged marine sediment revealed that residual salts are critical plant stressors whose adverse effects exceed those exhibited by high-level heavy metals and petroleum hydrocarbons present in the sediment. Acid washing and pH neutralization reduced not only the heavy metal contents but also the sediment salinity (by factors of 6.1–9.5), resulting in 100% germination of barley. For acid-washed and calcium-oxide-neutralized sediment, the barley growth was comparable to that observed in untreated and water washed sediment despite factors of 5.2–8.0 greater sediment salinity in the former. This result represents the protective effect of residual calcium against sodium and chloride toxicity. Water washing of acid-washed and pH-neutralized sediments further enhanced barley growth owing to the reduction in osmotic pressure. This study showed the effect of different sediment-washing reagents on the product quality. It also indicated the significance of balancing the enhancement of product quality and economic cost of further treatment requirements.

Fluxes of Water through Aquaporin 9 Weaken Membrane-Cytoskeleton Anchorage and Promote Formation of Membrane Protrusions

All modes of cell migration require rapid rearrangements of cell shape, allowing the cell to navigate within narrow spaces in an extracellular matrix. Thus, a highly flexible membrane and a dynamic cytoskeleton are crucial for rapid cell migration. Cytoskeleton dynamics and tension also play instrumental roles in the formation of different specialized cell membrane protrusions, viz. lamellipodia, filopodia, and membrane blebs. The flux of water through membrane-anchored water channels, known as aquaporins (AQPs) has recently been implicated in the regulation of cell motility, and here we provide novel evidence for the role of AQP9 in the development of various forms of membrane protrusion. Using multiple imaging techniques and cellular models we show that: (i) AQP9 induced and accumulated in filopodia, (ii) AQP9-associated filopodial extensions preceded actin polymerization, which was in turn crucial for their stability and dynamics, and (iii) minute, local reductions in osmolarity immediately initiated small dynamic bleb-like protrusions, the size of which correlated with the reduction in osmotic pressure. Based on this, we present a model for AQP9-induced membrane protrusion, where the interplay of water fluxes through AQP9 and actin dynamics regulate the cellular protrusive and motile activity of cells.

Hemopexin Is Protective Against Intravascular Hemolysis–Induced Vascular Damage

AbstractAbstract 3207 Background:Intravascular hemolysis renders hemoglobin (Hb), usually protected by the red blood cell environment, susceptible to oxidation to its ferric (metHb) form. Haptoglobin (Hp) provides first aid to protect the vasculature from acellular metHb havoc. However, once Hp is consumed, ferrous Hb readily undergoes oxidation to metHb, in which the globin to heme affinity is reduced. MetHb releases the loosely bound heme allowing it to execute its oxidative activity. While nucleated cells, like endothelial cells, are equipped with the heme oxygenase-1 defence system, the nucleus lacking red blood cells (RBC) and low density lipoproteins (LDL) particles have no defence from heme-induced oxidation. Therefore the sole defence from heme oxidative damage remains the plasma protein hemopexin (Hx), which binds hemin with high affinity comparable to that of globin. Following hemin binding, Hx undergoes conformational changes rendering the heme inaccessible thereby inactive. Aim:The current study is focused on the ability of plasma Hx to defend the vasculature from acellular Hb induced damage. Results:Hx defence from metHb damage was studied in the following projects: a) preventing in vitro LDL oxidation by metHb, b) decreasing in vitro lysis of red cells created by hypotonic and mechanical stress. (c) Exploring consumption of Hx in hemodialysis (HD) treated patients by measuring their Hx levels. (a) Methemoglobin iron is a central cause of LDL oxidation. This process initiates formation of blood vessel plaques and atherosclerosis development. This part of the study examined the effect of apoHx (lacking heme) on LDL oxidation by metHb. Incubation of isolated native LDL (nLDL) or vitamin E depleted (dLDL) with low concentration of metHb range (1-10μM) resulted in covalent apoB inter-particle crosslinking in both LDL types, dLDL being more sensitive than nLDL to the oxidative crosslinking. Addition of apoHx abolished metHb-induced oxidation even in the dLDL. This Hx activity (comparable to that of haptoglobin) was confirmed by both SDS-PAGE and fluorescent assay of bityrosines formation. The fact that Hx protects LDL, especially vitamin E depleted particles, shed light on the controversial antioxidant vitamin E properties by indicating its efficacy in defence against acellular Hb induced LDL oxidation. (b) Like LDL the red cell membrane is exposed to metHb-induced oxidative damage. Acellular Hb was formed by hypotonic shock or mechanical shear stress to fresh whole blood of healthy donors. The effect of Hx on acellular Hb levels was measured spectrophotometrically. Reduction of osmotic pressure in fresh blood to 40% of its normal value resulted in formation of ∼300 μM acellular Hb. Supplementation of exogenous apoHx (20μM) to blood before exposure to hypotonicity reduced acellular Hb formation by half. The specificity of Hx was proved by addition of up to 80μM albumin, which had no effect on acellular Hb concentration. Acellular Hb was formed also by applying shear stress on circulating fresh blood in narrow channels using a peristaltic pump. Within 4 hours acellular Hb reached ∼500μM. However, in presence of 20μM apoHx hemolysis was significantly reduced (up to 50%). This reduction may be attributed to Hx's ability to block the hemolysis amplifying effect of metHb on the RBC membrane. (c) In HD treated patients RBCs are exposed to the effects of recurrent mechanical shear stress. The last part of the research was dedicated to quantisation of apoHx levels (by titration with hemin) in sera of HD patients (n=60) prior to and immediately after a single dialysis procedure versus normal controls (n=20). Sera apoHx levels in HD patients prior to a dialysis session were lower compared to healthy controls (10.91±3.19 μM vs. 14.95±2.63 μM, p<0.05) and were even lower (7.49±3.8 μM) immediately after the treatment. These findings indicate that in the plasma of HD treated patients Hx consumption rate exceeds synthesis rate leading to a chronically low level of Hx. Moreover, reduction of Hx was even more prominent in patients on long term HD treatment of above five years. Conclusion:Hx is specifically effective in attenuation of acellular Hb damage to the vasculature. These results point to the option that treating HD patients with exogenous Hx may slow down the rate of atherosclerotic cardiovascular disease development, the major cause of morbidity and mortality in these patients. Disclosures:No relevant conflicts of interest to declare.

Formation of ovarian follicular fluid may be due to the osmotic potential of large glycosaminoglycans and proteoglycans

During mammalian follicle development, a fluid-filled antrum develops in the avascular centre of the follicle. We investigated the hypothesis that follicular fluid contains osmotically-active molecules, sufficiently large so as to not freely escape the follicular fluid. Such molecules could generate an osmotic differential and thus recruit fluid from the surrounding vascularised stroma into the antrum. Follicular fluid was collected from bovine follicles classified histologically as healthy (n = 4 pools) or atretic (n = 4 pools). Dialysis of the follicular fluid at 300 kDa or 500 kDa resulted in a reduction in colloid osmotic pressure of 35% and 60%, respectively, in fluid from healthy follicles and 29% and 80% from atretic follicles. Digestion of follicular fluid with Streptomyces hyaluronidase, chondroitinase ABC or DNase 1 followed by dialysis resulted in reductions in osmotic pressure of 43%, 53% and 43% respectively for fluids from healthy follicles and 34%, 20% and 31% for atretic follicles. Digestion with collagenase I, proteinase K, heparanase 1 or keratanase had no significant effect on the osmotic pressure of follicular fluid of healthy follicles. Ion exchange and size exclusion, Western blotting and ELISA identified the proteoglycans versican and inter-alpha trypsin inhibitor and the glycosaminoglycan hyaluronan in follicular fluid. We conclude that these molecules or aggregates of them are of sufficient size to contribute to the osmotic potential of follicular fluid and thus recruit fluid into the follicular antrum. DNA may also contribute but it is probably not a component that is regulated for this role.

Mechanosensitivity of GIRK Channels Is Mediated by Protein Kinase C-dependent Channel-Phosphatidylinositol 4,5-Bisphosphate Interaction

Gprotein-activated inwardly rectifying K+ channel (GIRK or Kir3) currents are inhibited by mechanical stretch of the cell membrane, but the underlying mechanisms are not understood. In Xenopus oocytes heterologously expressing GIRK channels, membrane stretch induced by 50% reduction of osmotic pressure caused a prompt reduction of GIRK1/4, GIRK1, and GIRK4 currents by 16.6-42.6%. Comparable GIRK current reduction was produced by protein kinase C (PKC) activation (phorbol 12-myristate 13-acetate). The mechanosensitivity of the GIRK4 current was abolished by pretreatment with PKC inhibitors (staurosporine or calphostin C). Neither hypo-osmotic challenge nor PKC activation affected IRK1 currents. GIRK4 chimera (GIRK4-IRK1-(Lys207-Leu245)) and single point mutant (GIRK4(I229L)), in which the phosphatidylinositol 4,5-bisphosphate (PIP2) binding domain or residue was replaced by the corresponding region of IRK1 to strengthen the channel-PIP2 interaction, showed no mechanosensitivity and minimal PKC sensitivity. IRK1 gained mechanosensitivity and PKC sensitivity by reverse double point mutation of the PIP2 binding domain (L222I/R213Q). Overexpression of Gbetagamma, which is known to strengthen the channel-PIP2 interaction, attenuated the mechanosensitivity of GIRK4 channels. In oocytes expressing a pleckstrin homology domain of PLC-delta tagged with green fluorescent protein, hypo-osmotic challenge or PKC activation caused a translocation of the fluorescence signal from the cell membrane to the cytosol, reflecting PIP2 hydrolysis. The translocation was prevented by pretreatment with PKC inhibitors. Involvement of PKC activation in the mechanosensitivity of muscarinic K+ channels was confirmed in native rabbit atrial myocytes. These results suggest that the mechanosensitivity of GIRK channels is mediated primarily by channel-PIP2 interaction, with PKC playing an important role in modulating the interaction probably through PIP2 hydrolysis.

Antidiarrhoeal Effect of Isolated Fraction (JC) of Jatropha curcas Roots in Mice

Objective : To study antidiarrhoeal activity of JC fraction isolated from Jatropha curcas L. roots in albino mice. Materials and methods : The roots of Jatropha curcas were collected from Awasari ghat near Pune, Maharashtra. The methanol extract of defatted roots was fractionated by solvent wash and preparative chromatography to yield JC fraction. This fraction at 50 and 100 mg/kg was tested for faecal output in normal and castor oil or magnesium sulphate induced diarrhoea in albino mice. The effect of JC fraction 100mg/kg was also studied on fluid and electrolyte secretion after castor oil administration and charcoal meal adsorption. Results : JC fraction showed activity against castor oil and magnesium sulphate induced diarrhoea . It also reduced intestinal motility as well as castor oil induced increased intraluminal fluid and sodium ion secretion in small intestine. Conclusion : JC fraction shows antidiarrhoeal activity through inhibition of prostaglandin biosynthesis and reduction of osmotic pressure. It also decreases peristaltic activity and castor oil induced permeability changes in intestinal mucosal membrane to water and electrolyte.

Effect of Osmotic Pressure on the Activation and Storage of Channel Catfish Sperm

Artificial spawning of channel catfish Ictalurus punctatus relies on the removal of testis and suspension of sperm in an extender solution for storage and use in fertilization. Little is known about the relationships among osmotic pressure, sperm activation, motility, and storage. Our objectives were to (1) estimate motility of channel catfish sperm diluted in solutions ranging in osmotic pressure from 8 to 295 milliosmols (mosmol)/kg, (2) identify the osmotic pressure that induces threshold activation (10% motility) and the highest pressure that induces complete activation, (3) determine the role of ionic dilution in activation by use of ion-deficient solutions, and (4) evaluate the effect of osmotic pressure on the retention of motility during storage. Motility (percentage of actively swimming sperm) was estimated in diluted Hanksˈ balanced salt solution (HBSS) and sucrose solutions over a range of osmotic pressures. The HBSS osmotic pressures of threshold and complete activation were 218 ± 15 mosmol/kg and 132 ± 9 mosmol/kg, respectively. We found that osmotic pressures above 220 mosmol/kg induced minimal (<10%) activation and pressures below 130 mosmol/kg induced complete activation. Within the zone of incomplete activation (220–130 mosmol/kg) a decrease of 15 mosmol/kg in osmotic pressure increased motility about 10%. We used sucrose solutions to provide an osmotic environment with minimal ionic influence for the testing of activation. Osmotic pressures for threshold (214 ± 1 mosmol/kg) and complete (125 ± 2 mosmol/kg) activation were consistent with those obtained with diluted HBSS, suggesting that reduction in osmotic pressure plays a major role in the activation of channel catfish sperm. Sperm stored in 122 mosmol/kg HBSS lost 82% of initial motility after 2.5 h. However, sperm stored in solutions with higher osmolalities retained motility significantly longer (P = 0.0017). A minimum reduction of osmotic pressure to below 130 mosmol/kg is essential to induce complete motility of channel catfish sperm for motility estimates and artificial fertilization.

Osmotic Pressure, Creaming, and Rheology of Emulsions Containing Nonionic Polysaccharide

We report measurements of the osmotic pressure, rheology, and creaming of concentrated oil-in-water emulsions (30 wt% mineral oil, 1 wt% surfactant, pH 7, ionic strength 0.05 M) as a function of the concentration of added nonionic polysaccharide dextran (5 × 105 Da). Experiments were carried out at 25°C on emulsions prepared with two different low-molecular-weight surfactants—nonionic Tween 20 (polyoxyethylenesorbitan monolaurate) and anionic SDS (sodium dodecyl sulfate). For both types of emulsifier, the addition of dextran was found to lead to a reduction in osmotic pressure, an increase in the limiting zero-shear-rate viscosity, and an enhancement in the rate of serum separation. These observations are consistent with the theory of depletion flocculation of the droplets by the nonadsorbing polymer. The effects of the surfactant type on emulsion properties are most evident at low or high dextran contents. The results are compared with those reported earlier for the same emulsions containing the anionic polysaccharide rhamsan. The combined data indicate a strong but complex relationship between creaming stability and low-stress creep rheological behavior. Substantial differences in properties between emulsions made with nonionic and charged surfactants indicate the importance of surfactant-biopolymer interactions in controlling the flocculation of emulsion droplets.

Quasi‐elastic neutron scattering in gels and solutions

AbstractMeasurements of swelling pressure, neutron spin‐echo scattering, and dynamic light scattering were made in an end‐linked poly(dimethylsiloxane) (PDMS) gel swollen to equilibrium in a good solvent (toluene) and also in the equivalent solution. The macroscopic osmotic modulus is depressed in the gel. Neutron spin echo observations at intermediate and high values of the scattering vector Q reveal that the mobility of the monomers is unaffected by cross‐linking. Elastic neutron scattering at small Q detects non‐uniformities in the polymer concentration distribution, which are absent from the solution. These non‐uniformities play a major role in the dynamic response of the system at lower Q, and and appear to be the cause of the observed reduction in osmotic pressure.

Preparation of lipid-free human hemoglobin by dialysis and ultrafiltration.

Dialysis of human red blood cells using a hypotonic solution and a commercial kidney dialysis unit followed by ultrafiltration through 0.1 micron pore hollow fibers provides an easily managed method for isolation of lipid-free hemoglobin. High pressure liquid chromatography analysis of lipid-free hemoglobin (LFHB) indicates 99-100% protein purity. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis demonstrated that LFHB migrates as a single band. The process requires hypoosmotic dialysis of human RBC to a final 119-139 (av 132) mosmol/kg osmotic pressure. Additional reduction in osmotic pressure results in irreversible cell lysis which results in lipid contamination of the hemoglobin. Processing one-half liter of packed red blood cells requires 10 h, resulting in an average of 90% hemoglobin recovery.

A continuous-flow high-yield process for preparation of lipid-free hemoglobin

Hypotonic hollow-fiber dialysis of bovine red blood cells followed by ultrafiltration through 0.1-μm pore hollow fibers provides a simple method for isolation of lipid-free hemoglobin. Hemoglobin (Hb) isolated by comparative techniques were all contaminated with membrane stroma. HPLC analysis of Hb revealed a protein peak of 99.6% purity and sodium dodecylsulfate-poly-acrylamide gel electrophoresis analysis revealed a single band. The process requires hypoosmotic dialysis of bovine RBC to a final 160–180 mosmol/kg osmotic pressure. Additional reduction in osmotic pressure causes irreversible cell lysis which leads to lipid contamination of the Hb. Processing of 1 2 liter of packed red blood cells requires 4–5 h, resulting in an average of 90% hemoglobin recovery.

Osmoregulatory and Hematological Responses of Rainbow Trout (Salmo gairdneri) to Extended Environmental Acidification

The dose-dependent relationships of several physiological responses to acid were examined in rainbow trout (Salmo gairdneri) exposed for 22 d to water at pH 4.2–6.0. Significant increases in ventilatory and cardiac rates occurred at pHw &lt; 4.9. Hematocrit and hemoglobin concentration increased progressively with acid stress at pHw &lt; 5.5. Plasma calcium, magnesium, sodium, and chloride concentrations were reduced and plasma phosphate elevated in acid-exposed fish. Seasonal differences were observed in the quantitative responses to acid exposure in the relationship between hematocrit and hemoglobin concentration and in the plasma concentrations of calcium and magnesium. The fractional contribution of sodium and chloride to plasma osmolality decreased linearly with increasing hydrogen ion concentration, and the change in plasma sodium, chloride, and osmolality per unit change in pHwwas 35.2 mmol/L, 39.7 mmol/L, and 47.4 mosmol/kg, respectively, in the pH range of 4.5–5.2. We concluded that the discrepancy between the reduction in plasma osmotic pressure and the combined reduction in the major plasma electrolytes is a result of the elevation in concentration of an unidentified plasma solute which offsets 40–45% of the expected reduction in osmotic pressure.

Association between Pelodera strongyloides (Nematoda: Rhabditidae) and wood mice, Apodemus sylvaticus.

Pelodera strongyloides larvae were found in the conjunctival sacs of Apodemus sylvaticus and Clethrionomys glareolus and in hair follicles of A. sylvaticus. Those in the eyes were 3rd-stage larvae while most of those in the dermis were early 4th stages. There was no evidence of pathology and sections of the skin showed that the nematodes of freshly killed mice and moulted once to the adult stage in 1-2 days at 15 degrees C. The stimulus to resume development appeared to be a reduction in temperature rather than presence of bacterial food or reduction in osmotic pressure. Countless generations ensued on nutrient agar provided the nematodes were periodically sub-cultured onto fresh agar. Nematodes from the eyes died in culture. Dauerlarvae of P. strongyloides were produced in exhausted cultures. They resumed development on fresh agar but not in distilled water. About half could be induced to exsheath by a temperature similar to that of mouse skin. A. sylvaticus probably accumulates nematode larvae in the dermis during its life and the nematodes resume development when the host dies.

The effects of salinity stress on the electrophysiological properties ofMya arenaria neurons

The euryhaline, osmoconforming bivalveMya arenaria is frequently subjected to large fluctuations in environmental salinity which are reflected by changes in the ionic and osmotic composition of the blood. These salinity-induced changes in the extraneuronal medium produce alterations in the electrical properties of neurons of the isolatedMya visceral ganglion. Following acute exposure ofMya neurons to reduced salinity, the resting membrane potential transiently hyperpolarizes and then abruptly depolarizes. These changes are accompanied by alterations in the apparent input resistance and, in addition, by a decrease in excitability, as evidenced by a loss or reduction of the TTX-sensitive action potentials. While a reduction in osmotic pressure produces some of these changes, others are produced by the reduced ionic concentration that also accompanies salinity stress. After several hours, the resting membrane potential repolarizes to near initial levels and the action potentials recover. Furthermore, neurons from animals acclimated to low salinity exhibit electrophysiological properties similar to those from neurons from animals kept in full-strength (100%) seawater, indicating that the neurons have adapted to the reduced environmental salinity.

Adaptation of mouse leukemic cells (L5178Y) to anisotonic media: II. Cell growth

In hypotonic media, with o smolarity as low as 185 mosM, mouse leukemic cells (L5178Y) are able to grow indefinitely but at a reduced rate compared with cells in normal medium. The change in growth rate is immediate, readily reversible, and dependent upon the initial cell concentration in the culture. At osmolarities below 185 mosM cells may undergo a few divisions, but some loss of viability is evident even if the cells are returned to normal medium after a short exposure. Failure of growth below 185 mosM is due to the reduction in osmotic pressure rather than the NaCl concentration of the medium, because the cells can grow at salt concentrations lower than 124 mosM if the osmotic pressure is maintained with sucrose. The factor that limits growth is probably the reduction in cellular K + associated with adaptation to media of reduced osmolarity. Growth is also inhibited when the osmolarity is raised above 400 mosM. Manipulation of the external K + concentration cannot extend the range of osmolarities that can support growth, although the rate of growth can be influenced.

Defect in poliovirus maturation under hypotonic conditions

Reduction of osmotic pressure in the medium in which poliovirus-infected cells are incubated results in inhibition of the formation of infectious virions and virus-specific particles sedimenting with the rate of mature virions. Under hypotonic conditions, however, synthesis of “soluble” virus-specific proteins and 74 S particles (procapsids) is observed. The 74 S particles formed under hypotonic and isotonic conditions do not differ from each other by sedimentation in sucrose density gradients, by buoyant density in CsCl, or by the spectrum of polypeptides detected by electrophoresis in polyacrylamide gel. No significant differences have been found in the set of polypeptides in the fraction of “soluble” proteins in extracts of productively or abortively infected cells. Taking into consideration earlier evidence that infectious poliovirus RNA is formed under hypotonic conditions (Tolskaya et al., 1966), a conclusion is drawn that under these conditions maturation of virions from the available precursors is disturbed.

THE MECHANISM OF AUXIN ACTION

Plant growth hormones are known to produce a number of striking effects on various processes including cell enlargement, root initiation, bud inhibition, etc. If has also been shown that the auxins, and indole-3-acetic acid in particular, participate in some general protoplasmic processes. Support for this view has been most recently afforded in the demonstration by Commoner and Thimann (1) that this hormone is involved in part of the respiratory metabolism of plant cells. The mechanism of the action of indole-3-acetic acid in the various growth processes which it influences is as yet unclear, however, even in the most favorable case of cell enlargement. Two theories concerning this auxin effect have been put forth. One suggests that the hormone lowers the resistance of the cell wall to turgor pressure, thereby permitting cell enlargement to take place. The other theory, suggested by Czaja (2), holds that cell enlargement is the result of an increase in the intensity of an osmotic driving force. Although it has been the practice to consider these as two opposing theories it must be pointed out that both agree that the actual driving force in cell enlargement is osmotic in nature for it is clear that the turgor pressure is itself a consequence of osmotic forces. No conclusive evidence in support of the wall-resistance theory has been presented thus far. The second theory has been objected to on the ground that growing plant cells do not show any increase in the osmotic pressure of their vacuole contents. The very failure of growing cells to exhibit a reduction in osmotic pressure while the vacuoles rapidly absorb water and increase in volume indicates, however, that the absolute solute content of the sap must be increased during this process. Thus it becomes important to know whether indole-3-acetic acid influences the solute content of the cell sap and so by momentarily increasing the osmotic pressure, affects water uptake and cell enlargement. It would be expected that no observable increase in osmotic pressure would occur, since the uptake of water would counteract the increase in solute content. Increase in sap solute might result from the hydrolysis of stored material such as protein and starch or from the absorption of salts. Attention toward the latter alternative was drawn by the observation of Thimann and Schneider