Increase In Osmolality Research Articles

Aspects of Acidosis in Ruminants with a Focus on Nutrition: A Review

An increased risk of acidosis in animals is associated with a high dry matter intake (DMI), which in turn results in the consumption of more fermentable organic matter (OM) in the rumen leading to a high production of volatile fatty acids (VFA). This is observed in lactating dairy cows and animals in a feedlot. Acute acidosis occurs when there is a severe drop in the pH of the rumen. A prolonged period when pH of in rumen remains low, it leads to sub-acute ruminal acidosis (SARA), which is a temporary imbalance between acid production and absorption. An associated change of an acute increase in the ruminal osmolarity and the accumulation of glucose and lactate in its stereoisomeric forms (D-lactate and L-lactate), is observed in the rumen fluid. However, in the sub-acute form, the accumulation of lactic acid occurs in the rumen. To a great extent, these changes in the rumen are due to high concentrations of VFA. The best way to avoid problems with ruminal acidosis is an adequate supply of neutral detergent fiber (NDF) in the diet, preferentially with large particle size and length to stimulate rumination and consequently greater buffering efficiency, thus maintaining the balance between pH and microorganisms in the rumen.

Effect of exercise-induced dehydration on circulatory markers of oxidative damage and antioxidant capacity.

Dehydration is a common event associated with exercise. However, few studies have examined the effects of dehydration on plasma redox status in humans. Eighty-two athletes were recruited and baseline anthropometrics and blood samples were obtained. Athletes then engaged in a dehydration protocol, training until 3% of preweight body mass was lost. Athletes returned to the lab and had postdehydration blood collected. Athletes then consumed an isotonic drink until pre-exercise body weight was reestablished. Blood was then recollected (1 h post full rehydration (PFR)). Samples were centrifuged and the plasma snap frozen in liquid nitrogen and stored at -80 °C. Lipid and protein oxidative stress was determined by measuring F2-isoprostanes and protein carbonyls (PC), respectively. Antioxidant capacity was determined by the ferric reducing ability of plasma (FRAP) and trolox equivalent antioxidant capacity (TEAC) assays. Plasma osmolality was determined using an osmometer. Statistical analysis utilized a 1-way ANOVA with posthoc testing. Values are reported as mean ± SD. Plasma osmolality was significantly elevated immediately postdehydration (p ≤ 0.001) but decreased to baseline at PFR. Plasma TEAC increased immediately postdehydration and at PFR (p ≤ 0.001). FRAP increased immediately postdehydration (p ≤ 0.001) and decreased to below baseline at PFR (p ≤ 0.05). Conversely, F2-isoprostanes declined significantly from baseline to immediately postdehydration and then significantly rose at PFR (p ≤ 0.001), whereas PC declined at PFR (p ≤ 0.01). This study indicates that dehydration and exercise cause a significant increase in plasma osmolality and antioxidant potential immediately postexercise. We propose dehydration significantly elevates antioxidant concentration which suppresses F2-isoprostanes and PC.

Protein Kinase R Mediates the Inflammatory Response Induced by Hyperosmotic Stress.

High extracellular osmolarity results in a switch from an adaptive to an inflammatory gene expression program. We show that hyperosmotic stress activates the protein kinase R (PKR) independently of its RNA-binding domain. In turn, PKR stimulates nuclear accumulation of nuclear factor κB (NF-κB) p65 species phosphorylated at serine-536, which is paralleled by the induction of a subset of inflammatory NF-κB p65-responsive genes, including inducible nitric oxide synthase (iNOS), interleukin-6 (IL-6), and IL-1β. The PKR-mediated hyperinduction of iNOS decreases cell survival in mouse embryonic fibroblasts via mechanisms involving nitric oxide (NO) synthesis and posttranslational modification of proteins. Moreover, we demonstrate that the PKR inhibitor C16 ameliorates both iNOS amplification and disease-induced phenotypic breakdown of the intestinal epithelial barrier caused by an increase in extracellular osmolarity induced by dextran sodium sulfate (DSS) in vivo Collectively, these findings indicate that PKR activation is an essential part of the molecular switch from adaptation to inflammation in response to hyperosmotic stress.

Durum Wheat Roots Adapt to Salinity Remodeling the Cellular Content of Nitrogen Metabolites and Sucrose

Plants are currently experiencing increasing salinity problems due to irrigation with brackish water. Moreover, in fields, roots can grow in soils which show spatial variation in water content and salt concentration, also because of the type of irrigation. Salinity impairs crop growth and productivity by inhibiting many physiological and metabolic processes, in particular nitrate uptake, translocation, and assimilation. Salinity determines an increase of sap osmolality from about 305 mOsmol kg−1 in control roots to about 530 mOsmol kg−1 in roots under salinity. Root cells adapt to salinity by sequestering sodium in the vacuole, as a cheap osmoticum, and showing a rearrangement of few nitrogen-containing metabolites and sucrose in the cytosol, both for osmotic adjustment and oxidative stress protection, thus providing plant viability even at low nitrate levels. Mainly glycine betaine and sucrose at low nitrate concentration, and glycine betaine, asparagine and proline at high nitrate levels can be assumed responsible for the osmotic adjustment of the cytosol, the assimilation of the excess of ammonium and the scavenging of ROS under salinity. High nitrate plants with half of the root system under salinity accumulate proline and glutamine in both control and salt stressed split roots, revealing that osmotic adjustment is not a regional effect in plants. The expression level and enzymatic activities of asparagine synthetase and Δ1-pyrroline-5-carboxylate synthetase, as well as other enzymatic activities of nitrogen and carbon metabolism, are analyzed.

Salivary diagnostic markers in males and females during rest and exercise

BackgroundSaliva is a useful diagnostic tool for analysis in sports, exercise and nutrition research, as collection is easy and non-invasive and it contains a large number of analytes affected by a range of physiological and pathological stressors and conditions. This study examined key salivary electrolytes and stress and immune markers in males and females at rest and during exercise.MethodsUnstimulated whole saliva from 20 healthy, recreationally active participants (8 males and 12 females) was analysed for flow rate, osmolality, sodium (Na+), potassium (K+), chloride (Cl−), secretory immunoglobulin A (SIgA), α-amylase activity and cortisol during both rest and moderate intensity (70% peak power) cycling exercise in a randomised crossover design. Each trial lasted 60 min and sampling was carried out at 15 and 45 min after the start of the trial. Saliva was collected using the gold-standard drool method; participants were required to provide at least 1 mL sample over 2 or 3-min period.ResultsFemales showed a greater response to steady-state exercise stress than males, with significant increases in osmolality (P < 0.001), α-amylase activity (P = 0.001) and secretion rate (P = 0.023) and SIgA secretion rate (P = 0.023), with trends for an increase in K+ (P = 0.053) and decrease in Cl− (P = 0.067). There were no differences between rest and exercise for any salivary analytes in males. In addition, females showed a trend for higher levels of cortisol than males at both rest (P = 0.099) and exercise (P = 0.070), as well as a higher heart rate (P < 0.001) and greater ratings of perceived exertion (P < 0.001) during the exercise trial. The coordination of the two stress response pathways (α-amylase vs cortisol) was positive in males (r = 0.799; P = 0.017) yet negative in females (r = −0.475; P = 0.036).ConclusionsMales and females show a markedly different response to steady-state exercise stress as measured in unstimulated whole saliva.

Bilateral tear film alterations in patients with unilateral quiescent herpes simplex keratitis

To evaluate bilateral tear function and corneal sensitivity in patients with unilateral quiescent herpes simplex keratitis (HSK) and determine the correlation between corneal sensitivity and tear secretion in both eyes. Thirty-five patients diagnosed with unilateral quiescent HSK and 35 heathy controls were included in this study. Bilateral tear osmolarity, Schirmer's test, the tear break-up time (TBUT) and corneal sensitivity were measured in all participants. In the HSK group, both eyes demonstrated a significant increase in tear osmolarity, and a decrease in Schirmer's test and the TBUT compared with healthy controls (All p<0.001). The bilateral tear osmolarity and Schirmer's test were similar, but the TBUT (4.9±2.1 versus 7.4±2.0second; p<0.001) and corneal sensitivity (35.1±1.9 versus 54.3±0.8mm; p<0.001) were significantly lower in the affected eyes. The bilateral tear osmolarity, Schirmer's test and the TBUT were significantly correlated with corneal sensitivity of the affected eye (All p<0.001). When corneal sensitivity of the unaffected eye was treated as a control variable, tear osmolarity (R=-0.626, p<0.001), Schirmer's test (R=0.739, p<0.001) and the TBUT (R=0.691, p<0.001) of the unaffected eyes were still significantly correlated with the corneal sensitivity of the affected eyes. Unilateral quiescent HSK causes bilateral tear impairment, which depends on the loss of corneal sensitivity in the affected eye. In the affected eye with severe corneal sensitivity loss, bilateral dry eye occurred.

Efficiency of Osmotic Concentration after Combined Treatment with Vasopressin and Blockage of Prostaglandin Synthesis.

We performed a complex functional study of the effects of prostaglandin synthesis blockage with diclofenac on manifestation of the hydroosmotic effect of vasopressin V2-receptor agonist desmopressin in the kidneys of Wistar rats with normal synthesis of endogenous vasopressin and homozygous Brattleboro rats with hereditary impaired synthesis of neurohypophyseal hormone vasopressin. Blockage of prostaglandin synthesis led to more pronounced increase in urine osmolality in Brattleboro rats than in Wistar rats due to elevation of not only urine but also sodium gradient at the expense of elimination of the inhibitory effect of prostaglandins on sodium reabsorption and membrane permeability for urine. During combined treatment, the effects of the hormone predominated: the increase in urine osmolality in Wistar and Brattleboro rats did not differ from that after desmopressin administration.

Incubation relative humidity induces renal morphological and physiological remodeling in the embryo of the chicken (Gallus gallus domesticus)

The metanephric kidneys of the chicken embryo, along with the chorioallantoic membrane, process water and ions to maintain osmoregulatory homeostasis. We hypothesized that changes in relative humidity (RH) and thus osmotic conditions during embryogenesis would alter the developmental trajectory of embryonic kidney function. White leghorn chicken eggs were incubated at one of 25–30% relative humidity, 55–60% relative humidity, and 85–90% relative humidity. Embryos were sampled at days 10, 12, 14, 16, and 18 to examine embryo and kidney mass, glomerular characteristics, body fluid osmolalities, hematological properties, and whole embryo oxygen consumption. Low and especially high RH elevated mortality, which was reflected in a 10–20% lower embryo mass on D18. Low RH altered several glomerular characteristics by day 18, including increased numbers of glomeruli per kidney, increased glomerular perfusion, and increased total glomerular volume, all indicating potentially increased functional kidney capacity. Hematological variables and plasma and amniotic fluid osmolalities remained within normal physiological values. However, the allantoic, amniotic and cloacal fluids had a significant increase in osmolality at most developmental points sampled. Embryonic oxygen consumption increased relative to control at both low and high relative humidities on Day 18, reflecting the increased metabolic costs of osmotic stress. Major differences in both renal structure and performance associated with changes in incubation humidity occurred after establishment of the metanephric kidney and persisted into late development, and likely into the postnatal period. These data indicate that the avian embryo deserves to be further investigated as a promising model for fetal programming of osmoregulatory function, and renal remodeling during osmotic stress.

Compliance as an Integral Part of the Dry Eye Syndrome Prevention Using Silicone Hydrogel Contact Lenses

The probability of dry eye syndrome (DES) in the patients using the Silicone-Hydrogel Contact Lenses is examined in many researches. Therefore, adhering to clinical recommendations is an important factor for DES prevention. The urgent issue is also a comprehensive assessment of functional parameters as pathogenetic base of DES.The objective of the research was tostudy DES development depending on compliance of silicone hydrogel contact lenses users.Matherials and methods. 97 patients (194 eyes) were included into the research. They formed 2 groups: group I with incomplete compliance (36 persons) and group II with complete compliance (61 persons). All the patients underwent the Norn’s test, Schirmer’s test, Jones test, tear film stability was defined. The probability of the dry eye syndrome development due to the subjective signs was also analysed.Results. The reliable decrease in the total (р&lt;0.05) and basale lacrimation (р&lt;0.05) indexes, the increase in osmolarity (р&lt;0.05) and decrease in tear film stability (р&lt;0.05) were detected in the patients who did not follow the clinical guidance during the Silicone-Hydrogel Contact Lenses wearing. In the same group the higher risk of dry eye syndrome development was verified (р&lt;0.05).Conclusion. Compliance disorder in the patients using Silicone-Hydrogel Contact Lenses was found to induce the reliable decrease in total and basale lacrimation, increase in osmolarity and tear stability disorder. All of this factors increase the risk of dry eye syndrome.

Media osmolality changes over 7 days following culture in a non-humidified benchtop incubator

Environmental stressors encountered in the IVF laboratory can negatively impact embryo development. Introduction of benchtop incubators and use of single-step uninterrupted culture methods aim to reduce harmful environmental deviations and improve system stability. However, evaporation and the subsequent increase in media osmolality could be induced from culture in the non-humidified environment present in many benchtop incubators, which could be amplified due to extended culture time with no media refreshment; especially in laboratories who culture embryos for up to 7 days.

The second messenger c-di-AMP inhibits the osmolyte uptake system OpuC in Staphylococcus aureus.

Staphylococcus aureus is an important opportunistic human pathogen that is highly resistant to osmotic stresses. To survive an increase in osmolarity, bacteria immediately take up potassium ions and small organic compounds known as compatible solutes. The second messenger cyclic diadenosine monophosphate (c-di-AMP) reduces the ability of bacteria to withstand osmotic stress by binding to and inhibiting several proteins that promote potassium uptake. We identified OpuCA, the adenosine triphosphatase (ATPase) component of an uptake system for the compatible solute carnitine, as a c-di-AMP target protein in S aureus and found that the LAC*ΔgdpP strain of S aureus, which overproduces c-di-AMP, showed reduced carnitine uptake. The paired cystathionine-β-synthase (CBS) domains of OpuCA bound to c-di-AMP, and a crystal structure revealed a putative binding pocket for c-di-AMP in the cleft between the two CBS domains. Thus, c-di-AMP inhibits osmoprotection through multiple mechanisms.

Effects of salinity on short-term waterborne zinc uptake, accumulation and sub-lethal toxicity in the green shore crab (Carcinus maenas)

Waterborne zinc (Zn) is known to cause toxicity to freshwater animals primarily by disrupting calcium (Ca) homeostasis during acute exposure, but its effects in marine and estuarine animals are not well characterized. The present study investigated the effects of salinity on short-term Zn accumulation and sub-lethal toxicity in the euryhaline green shore crab, Carcinus maenas. The kinetic and pharmacological properties of short-term branchial Zn uptake were also examined. Green crabs (n=10) were exposed to control (no added Zn) and 50μM (3.25mgL−1) of waterborne Zn (∼25% of 96h LC50 in 100 seawater) for 96h at 3 different salinity regimes (100%, 60% and 20% seawater). Exposure to waterborne Zn increased tissue-specific Zn accumulation across different salinities. However, the maximum accumulation occurred in 20% seawater and no difference was recorded between 60% and 100% seawater. Gills appeared to be the primary site of Zn accumulation, since the accumulation was significantly higher in the gills relative to the hepatopancreas, haemolymph and muscle. Waterborne Zn exposure induced a slight increase in haemolymph osmolality and chloride levels irrespective of salinity. In contrast, Zn exposure elicited marked increases in both haemolymph and gill Ca levels, and these changes were more pronounced in 20% seawater relative to that in 60% or 100% seawater. An in vitro gill perfusion technique was used to examine the characteristics of short-term (1–4h) branchial Zn uptake over an exposure concentration range of 3–12μM (200–800μgL−1). The rate of short-term branchial Zn uptake did not change significantly after 2h, and no difference was recorded in the rate of uptake between the anterior (respiratory) and posterior (ion transporting) gills. The in vitro branchial Zn uptake occurred in a concentration-dependent manner across different salinities. However, the rate of uptake was consistently higher in 20% seawater relative to 60% or 100% seawater – similar to the trend observed with tissue Zn accumulation during in vivo exposure. The short-term branchial Zn uptake was found to be inhibited by lanthanum (a blocker of voltage-independent Ca channels), suggesting that branchial Zn uptake occurs via the Ca transporting pathways, at least in part. Overall, our findings indicate that acute exposure to waterborne Zn leads to the disruption of Zn and Ca homeostasis in green crab, and these effects are exacerbated at the lower salinity.

In vivo organ specific drug delivery with implantable peristaltic pumps.

Classic methods for delivery of agents to specific organs are technically challenging and causes superfluous stress. The current study describes a method using programmable, implantable peristaltic pumps to chronically deliver drugs in vivo, while allowing animals to remain undisturbed for accurate physiological measurements. In this study, two protocols were used to demonstrate accurate drug delivery to the renal medulla. First, the vasopressin receptor-2 agonist, dDAVP, was delivered to the renal medulla resulting in a significant increase in water retention, urine osmolality and aquaporin-2 expression and phosphorylation. Second, in a separate group of rats, the histone deacetylase (HDAC) inhibitor, MS275, was delivered to the renal medulla. HDAC inhibition resulted in a significant increase in histone H3-acetylation, the hallmark for histone deacetylase inhibition. However, this was confined to the medulla, as the histone H3-acetylation was similar in the cortex of vehicle and MS275 infused rats, suggesting targeted drug delivery without systemic spillover. Thus, implantable, peristaltic pumps provide a number of benefits compared to externalized chronic catheters and confer specific delivery to target organs.

Adaptations of semen characteristics and sperm motility to harsh salinity: Extreme situations encountered by the euryhaline tilapia Sarotherodon melanotheron heudelotii (Dumeril, 1859)

In most teleost fishes, sperm cells are quiescent in the seminal plasma and are activated by either a drop (fresh water fish) or an increase in osmolality (marine fish) when released in the water. It is most interesting to examine how the mechanisms of sperm motility activation can adapt to a broad range of salinities, as applies to some euryhaline species, and particularly to the tilapia Sarotherodon melanotheron heudelotii, which can reproduce at salinities from 0 up to 120 in the wild. Here, the gonado-somatic index, semen characteristics, and the osmotic and ionic requirements of sperm motility activation were compared in S. m. heudelotii reared in fresh water (FW), sea water (SW), or hypersaline water (HW; salinities of 0, 35, and 70, respectively). No salinity-dependent differences were found in gonado-somatic index or semen characteristics, except for an increase of seminal plasma osmolality with increasing salinity (from 318 to 349 mOsm kg−1 in FW and HW fish, respectively). The osmolality range allowing the highest percentages of sperm activation broadened and shifted toward higher values with increasing fish ambient salinity (150–300, 300–800, and 500–1200 mOsm kg−1, for FW, SW, and HW fish, respectively). Nevertheless, at the three fish rearing salinities, sperm could be activated in media that were hypotonic, isotonic, or hypertonic relative to the seminal plasma, at least when some calcium was present above a threshold concentration. The [Ca2+] required for the activation of S. m. heudelotii sperm is (1) higher in fish reared at a higher salinity (2) higher in hypertonic than that in hypotonic activation media, whatever the fish rearing salinity, and (3) higher in the presence of Na+ or K+, the negative effects of which increased with an increase in fish rearing salinity. The [Ca2+]/[Na+] ​ ratios allowing for maximal sperm motility in SW or HW fish are close to those observed in natural environments, either in sea or hypersaline waters. In comparison to most teleosts with external fertilization, the total duration of sperm motility in S. m. heudelotii was exceptionally long (>2 hours regardless the fish rearing salinities). The decrease in sperm activity with increasing time since activation did not result from limiting energy reserves, as the addition of calcium in the activation medium caused most spermatozoa to become motile again. The comparison of sperm characteristics of S. m. heudelotii acclimated from FW to SW or HW with those of fish maintained all lifelong at their native salinity showed that adaptive responses were completed within 2 months or less.

(Pro)Renin Receptor Mediates Antidiuretic Action of Vasopressin/Prostaglandin EP4 Subtype

Within the kidney, (pro)renin receptor (PRR) is predominantly expressed in the collecting duct (CD), particularly in intercalated cells and is regulated by the EP4 subtype. Here we investigated the function of CD PRR during antidiuresis and defined its relationship with the EP4 subtype as well as vasopressin (VP). Water deprivation (WD) elevated renal PRR expression and urinary soluble PRR (sPRR) excretion in rats. Intrarenal infusion of a PRR decoy peptide PRO20 to rats partially attenuated the decrease in urine volume and the increase in urine osmolality in response to 48‐h WD, in parallel with suppressed aquaporin‐2 expression; a similar effect was seen with EP4 antagonism. The mice lacking PRR in the CD exhibited increased urine volume and decreased urine osmolality at basal condition and exhibited impaired urine concentrating capability after WD, accompanied with severe volume loss and a dangerous level of plasma hyperosmolality. In primary culture of rat inner medullary collecting duct (IMCD) cells, exposure to 10 nM prorenin for 24 h remarkably induced AQP2 protein expression, which was blunted by a PRR decoy inhibitor PRO20 and PRR siRNA. VP treatment for 24 h similarly induced aquaporin‐2 (AQP2) expression, accompanied with increased release of PGE2 and sPRR; the AQP2 upregulation was blunted by antagonism of EP4 or PRR. Overall, we have defined a VP/PGE2/EP4/PRR/AQP2 pathway that appears to play an important role in regulation of urine concentrating capability.Support or Funding InformationThis work was supported by National Institutes of Health Grants DK104072 and DK094956, VA Merit Review from the Department of Veterans Affairs, and National Natural Science Foundation of China Grant No. 91439205 and No. 31330037. T. Yang is a Research Career Scientist in the Department of Veterans Affairs.

Effects of Hyperosmotic Stress on Cellular Proteome and Phenotype of Tilapia (Oreochromis mossambicus) OmB Cells

Fish that inhabit an environment of fluctuating salinity (e.g. estuaries, intertidal zones) are frequently exposed to osmotic challenges. These euryhaline fish must cope with unpredictable salinity changes, and thus must respond quickly to alterations in environmental osmolality. Some euryhaline fish, e.g. tilapia, also face irregular and longer periods of high salinity, for instance during seasonal droughts in arid areas. Even though teleosts are osmoregulators, hyperosmotic stress leads to a significant increase in plasma osmolality. To prevent the detrimental effects that result from hyperosmotic stress if unaccounted for, cells must compensate for increased plasma osmolality. A previously immortalized Mozambique tilapia (Oreochromis mossambicus) cell line derived from the brain (OmB) was utilized to expose the mechanisms individual cells employ to survive this stress. Cultured cells were exposed to either control isosmotic media (300mOsm/kg), 450mOsm/kg, which is physiologically relevant for fish plasma, or maximum cellular tolerance levels of 700mOsm/kg for 8 days. Hyperosmotic medium was prepared by increasing NaCl concentration. Cell proliferation and time to confluency, as well as passage numbers, were monitored in treatment and control cells. The morphology and general appearance of experimental and control cells were also periodically monitored via phase contrast microscopy. In addition, proteins that are altered in their abundance by hyperosmolality were identified by label‐free quantitative proteomics to explain cellular phenotypes associated with hyperosmotic stress acclimation. Based on our results we conclude that the tilapia proteome is extensively and specifically modulated during hyperosmotic stress to adjust cellular physiology, stress tolerance, and morphology.Support or Funding InformationThis work was supported by National Science Foundation, IOB 1355098.

Coordination of Gene Expression and Cell Cycle Progression in Response to Stress; a Novel Checkpoint in S Phase

Exposure of cells to increases in extracellular osmolarity results in the activation of the Hog1 stress‐activated protein kinase (SAPK). Activation of Hog1 is required to generate a set of osmoadaptive responses essential for survival under high osmolarity. Adaptation to osmostress requires the induction of a large number of genes, which indicates the necessity to regulate several aspects of the cell physiology. In addition to gene expression, the SAPK also controls cell cycle. Here, we showed that the SAPK is able to modulate cell cycle delay in different phases of the cell cycle including S phase. During S phase, Hog1 controls Mrc1, a protein of the replication complex, to control DNA replication (Duch et al., 2013). The control of replication through Mrc1 is required to coordinate stress‐responsive gene induction with duplication of DNA upon osmostress. Remarkably, we have recently found that Mrc1 is also important to delay replication in response to other environmental stresses suggesting a conserved mechanism of S phase regulation upon transcriptional outbursts.Support or Funding InformationThis work was supported by grants from the Spanish Government (BFU2012‐33503 to F.P., BFU2014 52333 to E.d.N.) and the Fundación Marcelino Botín to F.P. F.P. and E.d.N. are recipients of an ICREA Academia (Generalitat de Catalunya).

Antidiuretic Action of Collecting Duct (Pro)Renin Receptor Downstream of Vasopressin and PGE2 Receptor EP4.

Within the kidney, the (pro)renin receptor (PRR) is predominantly expressed in the collecting duct (CD), particularly in intercalated cells, and it is regulated by the PGE2 receptor EP4 Notably, EP4 also controls urinary concentration through regulation of aquaporin 2 (AQP2). Here, we tested the hypothesis that sequential activation of EP4 and PRR determines AQP2 expression in the CD, thus mediating the antidiuretic action of vasopressin (AVP). Water deprivation (WD) elevated renal PRR expression and urinary soluble PRR excretion in rats. Intrarenal infusion of a PRR decoy peptide, PRO20, or an EP4 antagonist partially prevented the decrease in urine volume and the increase in urine osmolality and AQP2 expression induced by 48-hour WD. In primary cultures of rat inner medullary CD cells, AQP2 expression induced by AVP treatment for 24 hours depended on sequential activation of the EP4 receptor and PRR. Additionally, mice lacking PRR in the CD exhibited increased urine volume and decreased urine osmolality under basal conditions and impaired urine concentrating capability accompanied by severe volume loss and a dangerous level of plasma hyperosmolality after WD. Together, these results suggest a previously undescribed linear AVP/PGE2/EP4/PRR pathway in the CD for regulation of AQP2 expression and urine concentrating capability.

The effect on photosynthesis and osmotic regulation in Beta vulgaris L. var. Flavescens DC. by salt stress

This study was to investigate the effect of salt stress on physiological characteristics such as plant growth, photosynthesis, solutes related to osmoregulation of Beta vulgaris. A significant increase of dry weight was observed in 50 mM and 100 mM NaCl. The contents of Chl a, b and carotenoid were lower in NaCl treatments than the control. On 14 day after NaCl treatment, photosynthetic rate (PN), the transpiration rate (E) and stomatal conductance of CO2 (gs) were reduced by NaCl treatment. On 28 day after NaCl treatment, the significant reduction in g s and E was shown in NaCl 200 mM. However, PN and water use efficiency (WUE) in all NaCl treatments showed higher value than that of control. Total ion contents (TIC) and osmolality were higher than the control. On 14 day after treatment, the contents of proline (Pro) increased signifi cantly in 200 mM and 300 mM NaCl concentration compared with control, whereas on 28 day in all treatments it was lower than that of the control. The contents of glycine betaine (GB) increased with the increase of NaCl concentration. The contents of Na + , Cl , GB, osmolality and TIC increased with the increase of NaCl concentrations. These results suggested that under severe NaCl stress conditions, NaCl treatment did not induce photochemical inhibition on fluorescence in the leaves of B. vulgaris, but the reduction of chlorophyll contents was related in a decrease in leaf production. Furthermore, increased GB as well as Na + and Cl contents resulted in a increase of osmolality, which can help to overcome NaCl stress.

Contributions of Coulombic and Hofmeister Effects to the Osmotic Activation of Escherichia coli Transporter ProP.

Osmosensing transporters mediate osmolyte accumulation to forestall cellular dehydration as the extracellular osmolality increases. ProP is a bacterial osmolyte-H(+) symporter, a major facilitator superfamily member, and a paradigm for osmosensing. ProP activity is a sigmoid function of the osmolality. It is determined by the osmolality, not the magnitude or direction of the osmotic shift, in cells and salt-loaded proteoliposomes. The activation threshold varies directly with the proportion of anionic phospholipid in cells and proteoliposomes. The osmosensory mechanism was probed by varying the salt composition and concentration outside and inside proteoliposomes. Data analysis was based on the hypothesis that the fraction of maximal transporter activity at a particular luminal salt concentration reflects the proportion of ProP molecules in an active conformation. ProP attained the same activity at the same osmolality when diverse, membrane-impermeant salts were added to the external medium. Contributions of Coulombic and/or Hofmeister salt effects to ProP activation were examined by varying the luminal salt cation (K(+) and Na(+)) and anion (chloride, phosphate, and sulfate) composition and then systematically increasing the luminal salt concentration by increasing the external osmolality. ProP activity increased with the sixth power of the univalent cation concentration, independent of the type of anion. This indicates that salt activation of ProP is a Coulombic, cation effect resulting from salt cation accumulation and not site-specific cation binding. Possible origins of this Coulombic effect include folding or assembly of anionic cytoplasmic ProP domains, an increase in local membrane surface charge density, and/or the juxtaposition of anionic protein and membrane surfaces during activation.