Protaphorura tricampata, a euedaphic and highly permeable springtail that can sustain activity by osmoregulation during extreme drought

We have investigated drought physiology of soil dwelling springtails since water availability is a key environmental factor governing their performance, and predictions of climate change suggest increased frequency and intensity of summer droughts. Here we show in field and laboratory experiments that the typical euedaphic springtail, Protaphorura tricampata, can survive extreme drought and remain active in soils where the water potential is much lower than equivalent to normal osmotic pressure of springtails. Euedaphic springtails (i.e. species living in deeper soil layers) have an extraordinary ability to up-regulate osmotic pressure of body fluids and prevent water loss in soils where the water potential has dropped to well below the permanent wilting percentage of plants. The ability to regulate osmotic pressure of body fluids is based on accumulation of compatible osmolytes such as sugars and free amino acids. Alanine was the most important osmolyte in P. tricampata and accumulated to concentrations of about 300 μmol g⁻¹ dry weight. It is suggested that alanine also serves as a non-toxic storage of ammonia during drought periods where the normal urine production is hampered. The results presented here show, contrary to convention, that high cuticular permeability is not necessarily accompanied by poor drought tolerance, and is not a good predictor of drought susceptibility.     

Salinity--stress and Desiccation in Intertidal Worms

SYNOPSIS. Intertidal worms (oligochaetes, polychaetes, sipunculids)inhabiting beaches and tidal fiats both on the open sea coastand in estuaries may be exposed to significant tidal as wellas seasonal variations in salinity. However, there are veryfew measurements of the actual variations in salinity encounteredby worms in nature. Behavior (irrigation of burrow, verticalmovements in burrows, migration in gradients of salinity)maybe important in determining to which of the available salinitiesin a tidal cycle the worms may be exposed. In response to rapidlowering of salinity, worms gain water and lose salts, theseprocesses combining in diluting the internal fluids. Internalilution occurs more slowly in euryhaline species than in stenohalinespecies. Worms fully adapted to salinities lower than 30 % seawater may be hyperosmotic (demonstrated for six species of Nereidae).Mechanisms involved in hyperosmotic regulation include activetransport of salts(demonstrated in Nereis diversicolor), reductionofthe permeability of the body surface to salts and perhapsto water, and perhaps production of hypo—osmotic urine.Sipunculids can tolerate considerable loss of water rom dehydrationand concomitant increases in osmotic concentration of the bodyfluids. It is suggested that worms exposed to significant tidalvariations in salinity may seldom be in osmotic equilibriumwith their external medium.     

Enhanced drought tolerance of a soil-dwelling springtail by pre-acclimation to a mild drought stress

The springtail Folsomia candida has a highly permeable cuticle, but is able to survive several weeks at 98.2%RH. This corresponds to a water potential deficit of about 17bars between the environment and the normal osmotic pressure of the body fluids of this animal. Recent studies have shown a water vapour absorption mechanism by accumulation of sugars and polyols (SP) in F. candida, which explains how this species can survive dehydrating conditions. In the present study, adult F. candida were pre-acclimated at 98.2%RH to induce the accumulation of SP, and were subsequently exposed for additional desiccating conditions from 98 to 94%RH. Activity level, water content, osmotic pressure of body fluids and SP composition were investigated. After the desiccation period, the animals were rehydrated at 100%RH and survival was assessed. The results showed that F. candida survived a more severe drought stress when it had been pre-acclimated to 98.2%RH before exposure to lower humidity. This species was able to maintain hyperosmosity to the surroundings at 95.5%RH, suggesting that it can absorb water vapour down to this limit. Below this limit, trehalose levels increased while myo-inositol levels decreased. We propose that this is a change of survival strategy where F. candida at mild desiccation levels seek to retain water by colligative means (remain hyperosmotic), but at severe desiccation levels switches to an anhydrobiotic strategy.     

Elevated levels of colloid osmotic pressure in cecal contents of germfree animals.

Determinations of colloid osmotic pressure in the supernatant of germfree rat cecal contents indicated substantially elevated values in comparison to those of rat blood plasma or of conventional rat cecal supernatant. The germfree cecal supernatant, under conditions of similar total osmolality, was able to draw water at a sizable rate from a polyvinylpyrollidone solution whose colloid osmotic pressure was taken to be equivalent to that of interstitial fluid. It is suggested that the water absorption inhibition which was observed in the lower bowel of germfree rodents, is in part caused by the colloid osmotic pressure gradient which exists in these animals between the luminal contents and the tissue component.     

The significance of gut sucrase activity for osmoregulation in the pea aphid, Acyrthosiphon pisum

The osmotic pressure of the body fluids of aphids is lower than in their diet of plant phloem sap. It is hypothesised that aphids reduce the osmotic pressure of ingested food by sucrase-mediated hydrolysis of dietary sucrose to glucose and fructose, and the polymerisation of glucose into oligosaccharides of low osmotic pressure per hexose unit. To test this hypothesis, the impact of the alpha-glucosidase inhibitor acarbose on the sugar relations and osmoregulation of aphids was explored. Acarbose inhibited sucrase activity in gut homogenates and the production of monosaccharides and oligosaccharides in the honeydew of live aphids. Acarbose caused an increase in the haemolymph osmotic pressure for aphids reared on a diet (containing 0.75 M sucrose) hyperosmotic to the haemolymph and not on the isoosmotic diet containing 0.2 M sucrose. It did not affect aphid feeding rate over 2 days, except at high concentrations on 0.75 M sucrose diet, and this may have been a secondary consequence of osmotic dysfunction. Acarbose-treated aphids died prematurely. With 5 microM dietary acarbose, mean survivorship on 0.2 M sucrose diet was 4.2 days, not significantly different from starved aphids, indicating that, although these aphids fed, they were deprived of utilisable carbon; and on 0.75 M sucrose diet, mean survivorship was just 2.8 days, probably as a consequence of osmotic failure. It is concluded that the aphid gut sucrase activity is essential for osmoregulation of aphids ingesting food hyperosmotic to their body fluids.     

The importance of cuticular permeability, osmolyte production and body size for the desiccation resistance of nine species of Collembola

Euedaphic collembolans have recently been shown to actively regulate internal osmotic pressure by means of sugars and polyols in response to desiccation. In contrast, studies of cuticular permeability have shown that some, especially epedaphic, species of collembolans may primarily rely on a low cuticular permeability to survive desiccation. To elucidate to what extent these strategies are important for desiccation resistance, the survival of 7-day acute desiccation stress (LRH(50)), the cuticular water conductance constant and osmolyte production were investigated in nine species of collembolans, covering euedaphic, hemiedaphic and epedaphic species. The LRH(50) values ranging from 98.8% to 95.2% RH showed no correlation with the vertical distribution of species, since both the highest and lowest values were found in epedaphic species. The water conductance varied from 698+/-141 to 41+/-13 microg h(-1) cm(-2) mmHg(-1) and showed good agreement with the vertical distribution of species in their natural habitats. Modelling the drying curves showed that, in addition to cuticular permeability and osmolyte production, body size also plays an important role in the survival of short-term severe desiccation stress. Furthermore, the model pointed to the need for behavioural responses to desiccation, particularly in epedaphic species. Thus, in keeping with expected humidity regimes in their respective microhabitats, euedaphic species rely on small body size, high cuticular permeability and the ability to actively regulate the osmotic pressure of their body fluids, hemiedaphic species have similar strategies but with reduced cuticular permeability, whereas in epedaphic species, active regulation of osmotic pressure is replaced by combinations of greatly reduced cuticular permeability or greatly reduced surface area to volume ratio combined with behavioural responses to desiccation.     

Colloid Osmotic Pressure in Erythroblastosis Fetalis

Measurements were made of total proteins, albumin, and colloid osmotic pressure on cord blood samples from 15 infants with erythroblastosis fetalis (six of whom were hydropic) and from 151 non-rhesus non-hydropic control infants. The erythroblastotic infants had levels of total protein and albumin which fell within the normal range for gestational age, but their colloid osmotic pressures were abnormally low. It seems that low colloid osmotic pressure may provide a reasonable explanation for the occurrence of hydrops fetalis.     

An hypothesis on the role of cellular colloid osmotic pressure in determining behavior of cells in vitro including anchorage dependency and maintenance of the differentiated state

The osmotic problems involved when cells are isolated from tissues are analyzed. Evidence is considered which indicates that in vivo the Na pump is operating at maximal or near maximal rates and that this depends on low leak rates for salts and water due to various aspects of the tissues structure. Dispersion of the tissue results in breakdown of these barriers on free diffusion and the isolated cell is subjected to an enormous increase in passive influx due to colloid osmotic pressure without being able to increase its pumping rate to the extent needed to maintain volume control. It is proposed that the primary problem the cell faces in vitro is to compensate for the effective increase in its colloid pressure, e.g. the colloid osmotic pressure excess, emerging with the breakdown of the tissue structure. The finding that most normal cells have to adhere to a surface in order to grow or "anchorage dependency" is analyzed in terms of the way adhesion and spreading result in changes in ion and water movements into cells enabling them to achieve fluid balance in the face of the colloid pressure excess. It is also proposed that the differentiated state is more dependent on colloid osmotic balance than proliferation. The failure of conditions used in tissue culture to compensate adequately for the colloid pressure excess results in limiting the amount of protein which can be synthesized, dissipation of cellular energy, and changes in orientation of cellular components which contribute directly to the loss of differentiation which occurs during growth in vitro.     

Transcapillary fluid shifts in tissues of the head and neck during and after simulated microgravity.

To understand the mechanism, magnitude, and time course of facial puffiness that occurs in microgravity, seven male subjects were tilted 6 degrees head-down for 8 h, and all four Starling transcapillary pressures were directly measured before, during, and after tilt. Head-down tilt (HDT) caused facial edema and a significant elevation of microvascular pressures measured in the lower lip: capillary pressures increased from 27.7 +/- 1.5 mmHg (mean +/- SE) pre-HDT to 33.9 +/- 1.7 mmHg by the end of tilt. Subcutaneous and intramuscular interstitial fluid pressures in the neck also increased as a result of HDT, whereas interstitial fluid colloid osmotic pressures remained unchanged. Plasma colloid osmotic pressure dropped significantly by 4 h of HDT (21.5 +/- 1.5 mmHg pre-HDT to 18.2 +/- 1.9 mmHg), suggesting a transition from fluid filtration to absorption in capillary beds between the heart and feet during HDT. After 4 h of seated recovery from HDT, microvascular pressures in the lip (capillary and venule pressures) remained significantly elevated by 5-8 mmHg above baseline values. During HDT, urine output was 126.5 ml/h compared with 46.7 ml/h during the control baseline period. These results suggest that facial edema resulting from HDT is caused primarily by elevated capillary pressures and decreased plasma colloid osmotic pressures. The negativity of interstitial fluid pressures above heart level also has implications for maintenance of tissue fluid balance in upright posture.     

The osmoregulatory role of the filter-chamber in relation to phloem-feeding in Eurymela distincta (Cicadelloidea, Homoptera)

ABSTRACT. The cicadelloid leaf-hoppers, Eurymela distincta (Signoret) and Eurymela fenestrata (Le Pelletier & Serville), feed on the phloem sap of Eucalyptus spp. The osmotic pressure profile of haemolymph and gut fluids is consistent with a filtration mechanism based on passive osmosis. This is responsible for shunting water rapidly from foregut to hindgut in the relatively simple filter chamber. The osmotic gradient which drives the system is probably produced by active secretion of sodium and potassium into the Malpighian tubules and posterior midgut. Although the osmotic pressures in all parts of the system are higher, the mechanism is probably similar to that previously described for xylem-feeding cicadas.
The major haemolymph cations are sodium and magnesium and the concentrations of sodium and magnesium in the urine are higher than potassium. A variety of storage granules in the midgut contain calcium, phosphorus (as phosphate), ferric iron, zinc, magnesium, manganese and copper.     

Effect of acute lymphatic obstruction on fluid accumulation in the chest in dogs.

The effect of acute obstruction to lymphatic drainage on fluid accumulation in the lungs, pleura, and pericardium was assessed in the intact dog. Catheters were positioned in the venae cavase, right atrium (RA), left atrium (LA), age on fluid accumulation in the lungs, pleura, and pericardium was assessed in the intact dog. Catheters were positioned in the venae cavae, right atrium (RA), left atrium (LA), and aorta (Ao) of nine anesthetized, spontaneouly breathing dogs, and hydrostic and colloid osmotic pressures were continuously monitored. Lymphatic obstruction was achieved by raising systemic venous pressure to either 10 mmHg or 25 mmHg by a combination of fluid infusion and inflation of balloon catheters in the venae cavae for 2 h. The same constant net intravascular filtration pressure was maintained in both groups by appropriate use of saline or colloid-containing fluids. Pleural and pericardial fluids were measured postmortem and lung water content was determined by weighing before and after drying. Failure to detect greater fluid accumulation at the higher obstructing pressure (25 mmHg) than at the lower obstructing pressure (10 mmHg) suggests that over the range of obstructing pressures used there is no acute change in the magnitude of lymphatic drainage in the chest.     

Interstitial fluid pressure changes in pregnant rats

In pregnant rats significant interstitial fluid pressure changes could be detected by means of capsules chronically implanted into the subcutaneous tissue. The capsular pressure increased significantly from a control value of -4.3 +/- 0.5 mmHg to -0.7 +/- 0.5 mmHg during the first period of pregnancy. Immediately before parturition the capsular pressure returned to the control level. During lactation the pressure rose as high as + 0.5 +/- 0.9 mmHg. After lactation the pressure returned again to the control value. By determining the extracellular fluid and plasma volume, as well as protein concentration in plasma and capsular fluid, the hydrostatic and colloid osmotic forces operating in the extracellular space could be analysed. It has been concluded that the observed capsular pressure changes during pregnancy are not solely of volumetric or colloid osmotic origin.     

Antidiuresis immediately caused by drinking a small volume of hypertonic saline in man

The role of the oropharynx and larynx in body water regulationwas studied in human males by measuring urine volume and urineosmotic pressure at 20-min intervals before and after drinkinga very small volume (0.16 ml/kg body wt) of distilled water,isotonic (0.15 M) or hypertonic (0.30 M) saline. Only enoughof each test solution was taken to keep the oropharynx and larynxmoist continually for 20 min. Hypotonic diuresis resulted duringthe intake of distilled water (n = 9). In contrast to this,the intake of hypertonic saline produced quite opposite effectson urine volume and osmotic pressure, i.e. a hypertonic antidiuresis(n = 7). Isotonic saline had no effect on these two factorsin urine (n = 6). A significant linear relationship was notedbetween changes in the two factors and the concentration ofsodium chloride in the ingested water (P < 0.05). These resultssuggest that oropharyngeal and/or laryngcal afferents may contributeto the regulation of body water metabolism in humans, and thatthese afferents concerned with body water regulation dependupon the concentration of sodium chloride in the ingested solution.     

Buoyancy studies and microscopy of skin and subdermal extracellular matrix of the antarctic snailfish,Paraliparis devriesi

The Antarctic snailfish Paraliparis devriesi (Liparididae) occupies an epibenthic habitat at a depth of 500–650 m in the subzero waters of McMurdo Sound, Antarctica. Although lacking a swim bladder, this species is neutrally buoyant through the combined effects of reduced skeletal ossification and expansion of a watery gelatinous subdermal extracellular matrix (SECM). The SECM serves as a low density buoyancy agent. It comprises a mean of 33.8% of the body weight, the largest known proportion of any adult fish. The SECM is loose connective tissue dominated by ground substance consisting of glycosaminoglycans, especially hyaluronic acid, and immobilized water. Although the SECM is 97% water, elevated levels of NaCl provide an osmotic strength greater than that of other body fluids. Only small amounts of antifreeze compounds have been identified in P. devriesi; therefore, freezing avoidance may result from the combined effects of antifreezes and the elevated osmolality of body fluids. The skin overlying the SECM is thin (85–200 μm) and loose, and unlike most other fishes, the epidermis is several times thicker than the dermis. The midepidermis, has a distinctive layer of vacuolated club cells of unknown function. Light and electron microscopy indicate that the skin is unspecialized for protection against entry of ice. © 1994 Wiley-Liss, Inc.     

Identification of glycoconjugates in the urine of a patient with congenital disorder of glycosylation by high-resolution mass spectrometry

More than 150 molecular species were detected in a single glycoconjugate fraction obtained from urine of a congenital disorders of glycosylation (CDG) patient by use of high-resolution FT-ICR MS. With respect to its high-mass accuracy and resolving power, FT-ICR MS represents an ideal tool for analysis of single components in complex glycoconjugate mixtures obtained from body fluids. The presence of overlapping nearly isobaric ionic species in glycoconjugate mixtures obtained from CDG patient's urine was postulated from fragmentation data of several precursor ions obtained by nanoESI Q-TOF CID. Their existence was confirmed by high-resolution/high-mass accuracy FT-ICR MS detection. High-resolution FT-ICR mass spectra can, therefore, be generally considered for glycoscreening of complex mixture samples in a single stage. From the accurate molecular ion mass determinations the composition of glycoconjugate species can be identified. Particular enhancement of identification is offered by computer-assisted calculations in combination with monosaccharide building block analysis, which can be extended by considerations of non-carbohydrate modifications, such as amino acids, phosphates and sulfates. Taking advantage of this strategy, the number of compositions assigned to mass peaks was significantly increased in a fraction obtained from urine by size exclusion and anion exchange chromatography.     

Effect of salinity on oxygen consumption in fishes: a review

The effect of salinity on resting oxygen uptake was measured in the perch Perca fluviatilis and available information on oxygen uptake in teleost species at a variety of salinities was reviewed. Trans‐epithelial ion transport against a concentration gradient requires energy and exposure to salinities osmotically different from the body fluids therefore imposes an energetic demand that is expected to be lowest in brackish water compared to fresh and sea water. Across species, there is no clear trend between oxygen uptake and salinity, and estimates of cost of osmotic and ionic regulation vary from a few per cent to >30% of standard metabolism.     

Ultrastructure changes associated with osmoregulation in the hindgut cells of a saltwater insect, Ephydrella sp. (Ephydridae: Diptera)

Ephydrella larvae strictly regulate their blood osmotic pressure and Na⁺ content over a wide range of environmental salinities (7 mM to 3000 mM NaCl). They can survive in distilled water and 6000 mM NaCl for several days. In the hindgut the ileum is concerned with the regulation of urine composition whilst the rectum has a purely mechanical function. In the ileum there are large cells which have long basal channels and short apical microvilli, and small cells which have long apical leaflets and short basal channels. It is suggested that the large cells reabsorb water and that the small cells either reabsorb or secrete ions. The configurations of the channels, and the spacing of leaflets and microvilli change with alterations in environmental salinity. Fixation experiments using fixatives of different osmotic pressures show that the configuration of extracellular space in the cells has a marked dependence on both the osmotic pressure of the fixative and upon the environmental salinity. It is suggested that the osmotic response of the cells to fixatives indicates that the osmotic pressure of the cells increases with increasing environmental salinity. It is suggested, in general, that correlation of changes in the volume of extracellular space with changes in ion and water transport must be regarded with caution.     

Permeabilization of hepatocytes by a saponin and the effects of dextran.

The process by which a saponin derived from Gypsophila plants permeabilizes rat hepatocytes was studied. When monolayer cultures were incubated with 25 micrograms/ml saponin in phosphate buffered saline, the amount of cell-bound saponin increased for at least 90 min. Release of intracellular K+ started immediately, with a t1/2 of about 5 min. ATP and lactate dehydrogenase (LDH) began to appear in the medium only after lag periods of 10 to 20 min with t1/2s of 20 to 30 min. Removing the saponin from the medium after 15 min stopped any further release of ATP and LDH, showing that increased permeability to small ions alone does not lead to lysis by colloid osmotic pressure. However, the lysis that occurred upon 30 min continuous incubation with the saponin could be inhibited (delayed) by the addition of an osmotically active compound - a dextran. These results indicate that increasing binding of the saponin destabilizes the plasma membrane so that it will rupture from the colloid osmotic pressure.     

Effects of emperor moth larval secretions, hemolymph, and components on microorganisms and predators

The biological significance of the caterpillar scolus secretions, hemolymph, and compounds of four emperor moth species (Lepidoptera, Saturniidae) has been investigated by means of different biological tests and behavioral observations: 1. Larval body fluids and several components (e.g., phenylacetaldehyde) were shown to inhibit growth of certain bacteria but not of fungi. 2. Larval body fluids deter ants from feeding, evidently due to the strong behavior-modifying activity of several compounds therein. 3. Larval body fluids and whole caterpillars produce feeding-avoidance in model bird species. The findings suggest that these defensive mechanisms effectively protect saturniid caterpillars from pathogens and predators in nature.     

Concurrent quantitative HPLC–mass spectrometry profiling of small selenium species in human serum and urine after ingestion of selenium supplements

Selenium metabolic patterns in the human body originating from five distinct selenium dietary sources, selenate, selenite, selenomethionine (SeMet), methylselenocysteine (MeSeCys) and selenized yeast, were investigated by performing concurrent HPLC–mass spectrometric analysis of human serum and urine. Total selenium and selenium species time profiles were generated by sampling and analyzing serum and urine from volunteers treated with selenium supplements, up to 5 and 24 h following ingestion, respectively. We found that an increase in total serum selenium levels, accompanied by elevated selenium urinary excretion, was the common pattern for all treatments, except for that of selenite supplementation. Selenosugar 1 was a universal serum metabolite in all treatments, indicating that ingested selenium is favorably metabolized to the sugar. Except for selenite and selenized yeast ingestion, these patterns were reflected in the urine time series of the different treatments. Selenosugar 1 was the major selenium species present in urine in all treatments except for the selenate treatment, accounting for about 80% of the identified excreted species within 24 h of ingestion. Furthermore, the urinary metabolite trimethylselenonium ion (TMSe) was detected for the first time in human background serum by using HPLC coupled to elemental and molecular mass spectrometry. The concurrent monitoring of non-protein selenium species in both body fluids provides the relation between bioavailability and excretion of the individual ingested species and of their metabolic products, while the combined use of elemental and molecular mass spectrometry enables the accurate quantitation of structurally confirmed species. This successfully applied approach is anticipated to be a useful tool for more extensive future studies into human selenium metabolism.