Increase In Osmolality Research Articles

Differential effects of water loss and temperature increase on the physiology of fiddler crabs from distinct habitats

Temperature is one of the main environmental constraints to organism distribution, affecting physiology and survival. Organisms that inhabit the intertidal zone are exposed to temperature variation and, with climate change, they should face different conditions which include higher temperatures, leading to higher rates of water loss through evaporation and then fitness reduction or mortality. Here we tested the effects of desiccation and increased temperature in two fiddler crabs species that occupy distinct habitats in regard to vegetation cover and position on the intertidal zone and thus may respond differently to these stressors. Leptuca thayeri, which is restricted to the mid-tide zone and vegetated areas, had higher desiccation and mortality rates than Minuca rapax, a generalist species, when exposed to desiccation for 120 min. Also, compared to M. rapax, L. thayeri had a more permeable carapace. Temperature elevation of 10 °C and 20 °C for 72 h caused no mortality in either species. However, there were changes in hemolymph osmolality and muscle hydration in both species. Leptuca thayeri osmolality was low in the intermediate temperature, suggesting that at this temperature this species has a better salt secretion capability. Minuca rapax, however, had an increase in hemolymph osmolality at the highest temperatures with no LDH increase, which indicates that osmotic control in this species is more sensitive to temperature increase. Our results show that L. thayeri suffers more from desiccation, due to a more permeable carapace. However, because of this higher permeability L. thayeri is capable of lowering its temperature more than M. rapax. As temperature elevation produces great physiological changes in M. rapax, a reduced ability to keep a low temperature can be an issue for this species if temperature increases. However, higher water loss to keep body temperature low may decrease L. thayeri survivability in the same scenario.

Dystrophin 71 and α1syntrophin in morpho-functional plasticity of rat supraoptic nuclei: Effect of saline surcharge and reversibly normal hydration

Dystrophin (Dp) is a multidomain protein that links the actin cytoskeleton to the extracellular matrix through the dystrophin associated proteins complex (DAPC). Dp of 71 kDa (Dp71), corresponding to the COOH-terminal domain of dystrophin, and α1-syntrophin (α1Syn) as the principal component of the DAPC, are strongly expressed in the brain. To clarify their involvement in the central control of osmotic homeostasis, we investigated the effect of 14 days of salt loading (with drinking water containing 2% NaCl) and then reversibly to 30 days of normal hydration (with drinking water without salt), first on the expression by western-blotting and the distribution by immunochemistry of Dp71 and α1Syn in the SON of the rat and, second, on the level of some physiological parameters, as the plasma osmolality, natremia and hematocrit.Dp71 is the most abundant form of dystrophin revealed in the supraoptic nucleu (SON) of control rat. Dp71 was localized in magnocellular neurons (MCNs) and astrocytes, when α1Syn was observed essentially in astrocytes end feet. After 14 days of salt-loading, Dp71 and α1Syn signals decreased and a dual signal for these two proteins was revealed in the astrocytes processes SON surrounding blood capillaries. In addition, salt loading leads to an increase in plasma osmolality, natremia and hematocrit. Reversibly, after 30 days of normal hydration, the intensity of the signal for the two proteins, Dp71 and α1Syn, increased and approached that of control. Furtheremore, the levels of the physiological parameters decreased and approximated those of control.This suggests that Dp71 and α1Syn may be involved in the functional activity of the SON. Their localization in astrocyte end feet emphasizes their importance in neuronal–vascular–astrocyte interactions for the central detection of osmolality. In the SON, Dp71 and α1Syn may be involved in osmosensitivity.

Assessing Propylene Glycol Toxicity in Alcohol Withdrawal Patients Receiving Intravenous Benzodiazepines: A One-Compartment Pharmacokinetic Model.

While some case reports indicate that high doses of propylene glycol (PG) may result in metabolic acidosis, there has been no large-scale study that evaluatedthe risk of metabolic acidosis in patients receiving PG-containing benzodiazepines for acute alcohol withdrawal. This study was undertaken to evaluate the potential toxicity of PG in patients with acute alcohol withdrawal treated with intermittent intravenous bolus doses of diazepam and/or lorazepam. This is a retrospective case study using data collected from 18 randomly selected patients receiving one or both of these medications per a modified Clinical Institute Withdrawal Assessment for Alcohol (CIWA) Class 3 protocol. Plasma levels of PG were estimated using a one-compartment pharmacokinetic model. Only two patients had an elevated anion gap compared to their baseline value with one also experiencing a significant increase in serum creatinine. No increases in serum osmolarity were noted. Analysis showed that the benzodiazepine dose received was a good predictor of the estimated PG concentration (r=0.6), but was poorly correlated with the anion gap. No significant correlation was found with the creatinine clearance or serum creatinine. Patients receiving several daily doses were at higher risk of developing an anion gap (r=0.33), but the estimated maximum PG concentration did not correlate with the anion gap or serum concentration. It does not appear that intermittent bolus administration of intravenous benzodiazepines for alcohol withdrawal influenced renal function or anion gap regardless of number of administered doses, amount of PG received, or the estimated PG concentration.

Exercise and Asthma.

Transient airway narrowing can occur during or following exercise, a phenomenon called exercise-induced bronchoconstriction (EIB). The main mechanism of EIB is considered to be airway dehydration, resulting from increased ventilation during exercise. In asthma, such water loss causes an increase in airway fluid osmolarity, inducing airway smooth muscle contraction following the release of mediators from airway inflammatory cells. Asthmatics frequently experience EIB, but it may also be observed in others not reporting asthma symptoms, particularly elite endurance athletes. Individuals with asthma often refrain from performing physical exercise because they fear troublesome respiratory symptoms. However, in addition to its well-known cardiovascular and metabolic benefits, physical training has been shown to be beneficial for asthmatic adults and children in improving asthma control and asthma-related quality of life. Exercise training also reduces the risk of asthma exacerbations, improves exercise capacity, and decreases frequency and severity of EIB. To minimize the risk of EIB, asthma must be well controlled, and specific pharmacological and nonpharmacological preventative measures can be taken. Counterintuitively, in high-level athletes, the development of asthma, airway hyperresponsiveness, and EIB can be promoted by intense training over many years following exposure to environmental conditions, such as cold air, pollutants, and allergens. As for nonathletes, athletes must have optimal asthma control and apply preventative measures against EIB, taking into account antidoping regulations for asthma medications. A better understanding of the impact of exercise on asthma should improve the overall care of asthmatic patients.

Methodology for exposing avian embryos to quantified levels of airborne aromatic compounds associated with crude oil spills

Oil spills on birds and other organisms have focused primarily on direct effects of oil exposure through ingestion or direct body fouling. Little is known of indirect effects of airborne volatiles from spilled oil, especially on vulnerable developing embryos within the bird egg. Here a technique is described for exposing bird embryos in the egg to quantifiable amounts of airborne volatile toxicants from Deepwater Horizon crude oil. A novel membrane inlet mass spectrometry system was used to measure major classes of airborne oil-derived toxicants and correlate these exposures with biological endpoints. Exposure induced a reduction in platelet number and increase in osmolality of the blood of embryos of the chicken (Gallus gallus). Additionally, expression of cytochrome P4501A, a protein biomarker of oil exposure, occurred in renal, pulmonary, hepatic and vascular tissues. These data confirm that this system for generating and measuring airborne volatiles can be used for future in-depth analysis of the toxicity of volatile organic compounds in birds and potentially other terrestrial organisms.

Estudio «in vitro» de la influencia de la osmolaridad del plasma seminal en la morfología del espermatozoide

IntroductionSperm morphology is a parameter closely related to the fertility of the male gamete. Various infertility-causing disorders have been associated with anomalous sperm sub-populations that may be accompanied by an altered osmolality. A pilot study was conducted to determine whether the increase or decrease in in vitro osmolality can alter the original morphology. Material and methodsThe study included 42 randomly selected patients who had been classified as normal according to WHO criteria. The samples were processed by a CASA - SCA 5.4 (Sperm Class Analyzer) (Microptic S.L, Barcelona, Spain). Seminal plasma osmolality was measured using an Advanced Osmometer 2020 3MO. ResultsThe in vitro assays carried out on 30 patients showed that an osmolality increase up two times the reference value (880mOsm/kg), caused a progressive loss of sperm viability and a significant increase in macrocephalic sperm heads, with an increase in sperm volume and area. An osmolality decrease (half of the reference value, 228 mOsmol/kg) in a sample of 12 patients had no effect on sperm viability, although the sperm sub-population study showed increased micro-cephalic sperm with lower volume and cephalic area. DiscussionSperm morphology is acquired by sperm during the epididymal maturation. It was found that changing in vitro seminal plasma osmolality did not seem to affect it. Only extremely high values of osmolality cause the formation of macrocephalic sperm heads and a progressive loss of viability. These in vitro assays can help us to understand the biochemical seminal plasma effect in the male gamete.

Cold tolerance is linked to osmoregulatory function of the hindgut in Locusta migratoria.

There is growing evidence that maintenance of ion and water balance determines cold tolerance in many insects. The hindgut of terrestrial insects is critical for maintaining organismal homeostasis as it regulates solute and water balance of the haemolymph. Here, we used ex vivo everted gut sacs of Locustamigratoria to examine the effects of temperature (0-30°C), thermal acclimation, hypoxia, and ionic and osmotic forces on bulk water and ion (Na+, K+ and Cl-) movement across the rectal epithelium. These findings were related to simultaneous in vivo measurements of water and ion balance in locusts exposed to similar temperatures. As predicted, we observed a critical inhibition of net water and ion reabsorption at low temperature that was proportional to the in vivo loss of water and ion homeostasis. Further, cold-acclimated locusts, which are known to defend ion and water balance at low temperature, were characterised by improved reabsorptive capacity at low temperature. These findings strongly support the hypothesis that transport mechanisms in the hindgut at low temperature are essential for cold tolerance. The loss of osmoregulatory capacity at low temperature was primarily caused by reduced active transport, while rectal paracellular permeability to fluorescein isothiocyanate dextran was unchanged at 0 and 30°C. During cold exposure, water reabsorption was independent of major cation gradients across the epithelia, while a reduction in mucosal Cl- availability and an increase in mucosal osmolality markedly depressed water reabsorption. These findings are discussed in the context of existing knowledge and with suggestions for future physiological studies on cold acclimation and adaptation in insects.

Icodextrine : quels arguments pour et contre son utilisation comme agent osmotique en dialyse péritonéale ?

Icodextrin is a glucose polymer derived from starch that is used as an osmotic agent in peritoneal dialysis. Its high molecular weight limits blood absorption and is useful for long dwell since there is few osmotic gradient dispersal. Its benefits are numerous: ltrafiltration optimization and better salt and water control especially in anuric patients with a high peritoneal permeability and also in case of infectious peritonitis, glucose sparing with less metabolic complications and a better preservation of peritoneal membrane, better biocompatibility. However it should not be forgotten that icodextrin has also side effects that must be known: allergies, cases of aseptic peritonitis, overintense water and salt depletion, lymphatic absorption of icodextrin and its metabolites (including maltose) with a risk of false capillary glucose rate estimation and a moderate increase in plasma osmolality. That is why it is not recommended now to use more than one daily icodextrin dwell. Nevertheless, several dialysis units use icodextrin in more than one daily dwell, especially in patients with an important ultrafiltration loss or in those in whom glucose sparing is essential. It seems to profit them with no more side effects. A large multicenter trial is in progress to test the efficacy and safety of icodextrin dwell twice a day in elder incident patients in peritoneal dialysis (DIDo). Moreover, icodextrin is also used combined with glucose in a long dwell (bimodal ultrafiltration) with encouraging results in terms of ultrafiltration and glucose sparing.

Development of hyper osmotic resistant CHO host cells for enhanced antibody production

Cell culture platform processes are generally employed to shorten the duration of new product development. A fed-batch process with continuous feeding is a conventional platform process for monoclonal antibody production using Chinese hamster ovary (CHO) cells. To establish a simplified platform process, the feeding method can be changed from continuous feed to bolus feed. However, this change induces a rapid increase of osmolality by the bolus addition of nutrients. The increased osmolality suppresses cell culture growth, and the final product concentration is decreased. In this study, osmotic resistant CHO host cells were developed to attain a high product concentration. To establish hyper osmotic resistant CHO host cells, CHO-S host cells were passaged long-term in a hyper osmotic basal medium. There were marked differences in cell growth of the original and established host cells under iso- (328mOsm/kg) or hyper-osmolality (over 450mOsm/kg) conditions. Cell growth of the original CHO host cells was markedly decreased by the induction of osmotic stress, whereas cell growth of the hyper osmotic resistant CHO host cells was not affected. The maximum viable cell concentration of hyper osmotic resistant CHO host cells was 132% of CHO-S host cells after the induction of osmotic stress. Moreover, the hyper osmotic resistant characteristic of established CHO host cells was maintained even after seven passages in iso-osmolality basal medium. The use of hyper osmotic resistance CHO host cells to create a monoclonal antibody production cell line might be a new approach to increase final antibody concentrations with a fed-batch process.

Regulation of potassium dependent ATPase (kdp) operon of Deinococcus radiodurans.

The genome of D. radiodurans harbors genes for structural and regulatory proteins of Kdp ATPase, in an operon pattern, on Mega plasmid 1. Organization of its two-component regulatory genes is unique. Here we demonstrate that both, the structural as well as regulatory components of the kdp operon of D. radiodurans are expressed quickly as the cells experience potassium limitation but are not expressed upon increase in osmolarity. The cognate DNA binding response regulator (RR) effects the expression of kdp operon during potassium deficiency through specific interaction with the kdp promoter. Deletion of the gene encoding RR protein renders the mutant D. radiodurans (ΔRR) unable to express kdp operon under potassium limitation. The ΔRR D. radiodurans displays no growth defect when grown on rich media or when exposed to oxidative or heat stress but shows reduced growth following gamma irradiation. The study elucidates the functional and regulatory aspects of the novel kdp operon of this extremophile, for the first time.

Water restriction causes an intergenerational trade‐off and delayed mother–offspring conflict in a viviparous lizard

Abstract Parenting is costly and because the relationship between the mother and embryos is not mutualistic, mother–offspring conflicts may exist whenever resource are scarce. However, intergenerational trade‐offs and conflicts resulting from limited access to water, a vital and depreciable resource, remain largely overlooked. In this study, we examined the physiological, reproductive and life‐history responses to water restriction in the European Common Lizard (Zootoca vivipara). We hypothesized that, under water‐limited conditions, pregnant females experience both short‐term and long‐term physiological impacts (dehydration and stress) underlying an allocation trade‐off for water between mothers and offspring. Water restriction led to a decrease in body mass, and an increase in plasma osmolality (dehydration) and corticosterone concentration in both males and females. The extent of the dehydration was positively correlated with fecundity in females. This suggests a trade‐off between maternal water balance and allocation of water to developing embryos during reproduction. Water restriction had no immediate effect on reproductive output or offspring morphology at birth. Yet, water restriction in pregnant females enhanced their reproductive effort the following year but reduced the early life growth and annual survival of their second‐year offspring. These delayed fitness responses to water restriction in offspring and mothers suggest that water can trigger intergenerational conflicts as demonstrated for energy. Although the mediation of this conflict remains to be clarified, we hypothesized that it represents a selective force that influences reproductive strategies. A plain language summary is available for this article.

A comparison of anticonvulsant efficacy and action mechanism of Mannitol vs Phenytoin in adult rat neocortical slices

We show that, in adult rat neocortical slices, an anticonvulsant effect comparable to that of Phenytoin can be obtained through a Mannitol-induced increase in extracellular osmolarity of only 30mOsm/L. The anticonvulsant action of extracellular hyperosmolarity has been known for decades but has not found a feasible therapeutic application, yet. A 30mOsm/L increase in extracellular osmolarity is already utilized in neurocritical care though not as an anticonvulsant agent: the data suggest a possible effective anticonvulsant use, too, in this setting.We used multiple electrode arrays to characterize and compare the anticonvulsant mechanisms of Mannitol and Phenytoin. Phenytoin decreased the voltage, duration and spatial spread of rhythmic repetitive, ictal-like activity. In contrast, Mannitol did not significantly affect voltage, duration and spatial spread of rhythmic repetitive, ictal-like activity but rather it inhibited the rate of epileptiform discharges.

Osmoregulation and muscle water control of the Amazon fish Oscar Astronotus ocellatus (Cichlidae) when facing salinity stress

ABSTRACTSpecimens of Oscar Astronotus ocellatus from a fish farm were abruptly submitted to salt stress of 14 ppt and 20 ppt, for 3 and 8 h to determine their plasma osmolality. Muscle wet body mass change in vitro was analyzed from control freshwater animals. Fish in 14 ppt presented no osmolality distress even after 8 h. In 20 ppt, a slight increase (10%) in plasma osmolality was observed for both times of exposure when compared to control fish. Muscle slices submitted in vitro to hyper-osmotic saline displayed decreased body mass after 75 min, and slices submitted to hypo-osmotic saline displayed increased body mass after 45 min when compared to control (isosmotic saline). These results reinforce A. ocellatus’s euryhalinity. The fish were able to regulate its internal medium and tolerate 14 ppt, but presented an intense osmotic challenge and low muscle hydration control when facing salinities of 20 ppt.

A comparison of freezing-damage during isochoric and isobaric freezing of the potato.

BackgroundFreezing is commonly used for food preservation. It is usually done under constant atmospheric pressure (isobaric). While extending the life of the produce, isobaric freezing has detrimental effects. It causes loss of food weight and changes in food quality. Using thermodynamic analysis, we have developed a theoretical model of the process of freezing in a constant volume system (isochoric). The mathematical model suggests that the detrimental effects associated with isobaric freezing may be reduced in an isochoric freezing system. To explore this hypothesis, we performed a preliminary study on the isochoric freezing of a produce with which our group has experience, the potato.MethodExperiments were performed in an isochoric freezing device we designed. The device is robust and has no moving parts. For comparison, we used a geometrically identical isobaric freezing device. Following freezing and thawing, the samples were weighed, examined with colorimetry, and examined with microscopy.ResultsIt was found that potatoes frozen to −5 °C in an isochoric system experienced no weight loss and limited enzymatic browning. In contrast the −5 °C isobaric frozen potato experienced substantial weight loss and substantial enzymatic browning. Microscopic analysis shows that the structural integrity of the potato is maintained after freezing in the isochoric system and impaired after freezing in the isobaric system.DiscussionTissue damage during isobaric freezing is caused by the increase in extracellular osmolality and the mechanical damage by ice crystals. Our thermodynamic analysis predicts that during isochoric freezing the intracellular osmolality remains comparable to the extracellular osmolality and that isochoric systems can be designed to eliminate the mechanical damage by ice. The results of this preliminary study seem to confirm the theoretical predictions.ConclusionThis is a preliminary exploratory study on isochoric freezing of food. We have shown that the quality of a food product preserved by isochoric freezing is better than the quality of food preserved to the same temperature in isobaric conditions. Obviously, more extensive research remains to be done to extend this study to lower freezing temperatures and other food items.

Hyperthermia and extracellular hyperosmolality affect sarcolemmal damage and protein oxidation in mammalian skeletal muscle in vitro

In the US Armed Services, the incidence of rhabdomyolysis is 5–7 fold higher in peak summer months, suggesting that muscle membrane injury could be amplified by heat or to secondary dehydration. In this study we tested the extent each of these variables influences damage by evaluating sarcolemmal integrity and ROS‐induced protein oxidation. Extensor digitorum longus (EDL) and soleus (SOL) muscles were dissected from 24 adult male C57BL6J mice and placed at optimal length in tissue baths containing 4 ml of Krebs (95%O2/5%CO2). Muscles were intermittently stimulated to perform non‐fatiguing twitches for 30 min. Buffer temperature and osmolality were manipulated to provide four experimental conditions: normothermia/isotonic (35°C and 285 mOsm/kg), normothermia/hypertonic (35°C and 300 mOsm/kg), hyperthermia/isotonic (41°C and 285 mOsm/kg), and hyperthermia/hypertonic (41°C and 300 mOsm/kg). We quantified the integrity of the sarcolemma using both procion orange leakage into the fibers and a fluorometric assay to detect leakage out of double‐stranded cell‐free DNA (cfDNA). To assess protein oxidation, we performed immunoblot assays for protein carbonyl derivatives. For SOL we did not observe a significant effect of hyperthermia and/or hyperosmolality on procion orange leakage, but we observed an increase in cfDNA (p = 0.03) and protein carbonyls with hyperthermia (p = 0.02). Interestingly, these effects were absent when hyperosmolality was superimposed on hyperthermia. For EDL, an increase in procion orange leakage was observed with hyperthermia alone (p = 0.04) and when hyperthermia and hyperosmolality were combined (p = 0.03), but the combination did not elicit changes in cfDNA in the buffer. EDL protein carbonyls were independently augmented with hyperthermia (p = 0.01) and hyperosmolality (p = 0.02), but also did not increase when hyperthermia was combined with hyperosmolality. In conclusion, hyperthermia caused sarcolemma damage in EDL muscle, both alone and when combined with hyperosmolality. SOL was more resistant to hyperthermia‐induced procion orange leakage, despite an increase release of extracellular cfDNA. Furthermore, physiological increases in extracellular osmolality prevented protein oxidation in hyperthermia in both muscle types. These observations suggest that different muscle types may respond differently to hyperthermic and osmotic challenges. The compensatory effect of hyperosmolality on hyperthermia‐induced oxidative stress is consistent with a role for ROS production in compensatory responses to cell swelling in the heat.Support or Funding InformationSupported by the BK and Betty Stevens Endowment and the Brazilian Council for the Development of Science and Technology (CNPq no. 249094/2013‐4).

Salt Loading Activates Microglia and Increases Grooming Time and Time Spent Mobile in the Forced Swim Test: Is High Salt Intake a Causal Factor Linking Hypertension and Anxiety?

Hypertension and psychiatric disorders are major contributors to worldwide disability and are often co‐morbid; however, a shared pathogenic mechanism has not been identified. In models of neurogenic hypertension, high dietary salt (NaCl) drives microglial activation and stimulates production of proinflammatory cytokines. Cytokines promote action potential firing of pre‐sympathetic neurons in brain regions that regulate blood pressure, such as the hypothalamic paraventricular nucleus (PVN), and thereby likely contribute to development of neurogenic hypertension. Of special note is that neuroinflammation has likewise been implicated in the pathogenesis of depression and anxiety. Therefore, we hypothesized that high dietary salt concurrently drives microglial activation in blood pressure and mood regulating and synaptically connected brain regions, such as the PVN and amygdala, thereby promoting hypertension and yielding depression‐ and/or anxiety‐like behaviors. To test this, C57BL/6 mice were salt loaded (drinking 2 or 4% NaCl in water) for 1 week. Mice were then subjected to the forced swim test (FST), a screen for behavioral despair, and time spent grooming was assessed as a measure of anxiety‐like behavior. We found salt loading increased time spent mobile in the FST (P<0.01) and time spent grooming (P<0.01), both of which also result from acute administration of anxiogenic drugs, such as pentylenetrazole. Although findings suggest that salt loading induces anxiety‐like effects, additional studies utilizing alternative and complementary measures of anxiety‐like behavior are needed to affirm this interpretation. Hematology data support an anxiogenic action of salt loading since time spent mobile in the FST was positively correlated with the increase of plasma osmolality (P<0.01). Immunohistochemistry staining for ionized calcium‐binding adaptor molecule 1 (Iba1), a marker of microglial activation, was used to index tissue inflammation, and c‐Fos staining was used to identify transcriptionally activated neurons. Preliminary data showed salt loading increased Iba1 and c‐Fos positive cell staining in the PVN and the basolateral nucleus of the amygdala. To determine if behavioral effects of salt loading were dependent on microglial activation, minocycline, an inhibitor of microglial activation, was administered (100 mg/kg/day) in drinking water for 36 h before and during salt loading for 1 week. Preliminary data showed minocycline attenuated salt loading induced increases in time spent mobile in the FST and time spent grooming. These data suggest that even short‐term salt loading prompts microglial activation and transcriptional activation in limbic brain regions capable of producing anxiety‐like behavior. Future studies are needed to determine transcriptional consequences of microglial activation and to identify synaptic/intrinsic neuronal adaptations that generate this apparent salt loading induced anxiety phenotype in mice.Support or Funding InformationSupport: 5T32HL007446 (NCM), HL088052 (GMT)

Osmotic activation of a Ca2+-dependent phospholipase C pathway that regulates ∆N TRPV1-mediated currents in rat supraoptic neurons.

The magnocellular neurosecretory cells (MNCs) of the hypothalamus regulate body fluid balance by releasing the hormones vasopressin (VP) and oxytocin (OT) in an osmolality‐dependent manner. Elevations of external osmolality increase MNC firing and hormone release. MNC osmosensitivity is largely due to activation of a mechanosensitive non‐selective cation current that responds to osmotically‐evoked changes in MNC volume and is mediated by an N‐terminal variant of the TRPV1 channel (∆N TRPV1). We report a novel mechanism by which increases in osmolality may modulate ∆N TRPV1‐mediated currents and thus influence MNC electrical behaviour. We showed previously that acute elevations of external osmolality activate the enzyme phospholipase C (PLC) in isolated MNCs. We now show that the osmotic activation of PLC has a time course and dose‐dependence that is consistent with a role in MNC osmosensitivity and that it contributes to the osmotically‐evoked increase in non‐selective cation current in MNCs through a protein kinase C‐dependent pathway. We furthermore show that the mechanism of osmotic activation of PLC requires an increase in internal Ca2+ that depends on influx through L‐type Ca2+ channels. Our data therefore suggest that MNCs possess an osmotically‐activated Ca2+‐dependent PLC that contributes to the osmotic activation of ∆N TRPV1 and may therefore be important in MNC osmosensitivity and in central osmoregulation.

Stochastic and Differential Activation of σB and PrfA in Listeria monocytogenes at the Single Cell Level under Different Environmental Stress Conditions.

During host infection, the foodborne pathogen Listeria monocytogenes must sense and respond to rapidly changing environmental conditions. Two transcriptional regulators, the alternative sigma factor B (σB) and the Positive Regulatory Factor A (PrfA), are key contributors to the transcriptomic responses that enable bacterial survival in the host gastrointestinal tract and invasion of host duodenal cells. Increases in temperature and osmolarity induce activity of these proteins; such conditions may be encountered in food matrices as well as within the host gastrointestinal tract. Differences in PrfA and σB activity between individual cells might affect the fate of a cell during host invasion, therefore, we hypothesized that PrfA and σB activities differ among individual cells under heat and salt stress. We used fluorescent reporter fusions to determine the relative proportions of cells with active σB or PrfA following exposure to 45°C heat or 4% NaCl. Activities of both PrfA and σB were induced stochastically, with fluorescence levels ranging from below detection to high among individual cells. The proportion of cells with active PrfA was significantly higher than the proportion with active σB under all tested conditions; under some conditions, nearly all cells had active PrfA. Our findings further support the growing body of evidence illustrating the stochastic nature of bacterial gene expression under conditions that are relevant for host invasion via food-borne, oral infection.

Isochoric and isobaric freezing of fish muscle

We have recently shown that, a living organism, which succumbs to freezing to −4 °C in an isobaric thermodynamic system (constant atmospheric pressure), can survive freezing to −4 °C in an isochoric thermodynamic system (constant volume). It is known that the mechanism of cell damage in an isobaric system is the freezing caused increase in extracellular osmolality, and, the consequent cell dehydration. An explanation for the observed survival during isochoric freezing is the thermodynamic modeling supported hypothesis that, in the isochoric frozen solution the extracellular osmolality is comparable to the cell intracellular osmolality. Therefore, cells in the isochoric frozen organism do not dehydrate, and the tissue maintains its morphological integrity. Comparing the histology of: a) fresh fish white muscle, b) fresh muscle frozen to −5 °C in an isobaric system and c) fresh muscle frozen to −5 °C I in an isochoric system, we find convincing evidence of the mechanism of cell dehydration during isobaric freezing. In contrast, the muscle tissue frozen to −5 °C in an isochoric system appears morphologically identical to fresh tissue, with no evidence of dehydration. This is the first experimental evidence in support of the hypothesis that in isochoric freezing there is no cellular dehydration and therefore the morphology of the frozen tissue remains intact.

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.