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At least 145 records · Page 8Linked to original sources
PubMed2004

Thermo-osmoregulation of heat-labile enterotoxin expression by Escherichia coli.

Enterotoxigenic Escherichia coli causes diarrhea by producing several virulence factors including heat-labile enterotoxin (LT). LT is maximally expressed at 37 degrees C. The histone-like nucleoid structuring protein (H-NS) appears to inhibit LT expression by binding to a downstream regulatory element (DRE) at low temperatures. An hns+ E. coli strain, X7026, carrying an LT-beta-galactosidase translational fusion plasmid (pLT-lac) was shown to be responsive to varying amounts of sodium chloride (NaCl) as well as sucrose or lithium chloride. Maximal responsiveness to the various osmolytes was obtained with cells grown at 37 degrees C under microaerophilic conditions. Temperature-osmotic upshift experiments demonstrate LT expression is thermo-osmoregulated. pLT-lac was tested in an hns strain or its congenic hns+ strain for its response to NaCl. LT expression is elevated in the hns strain regardless of NaCl concentration and retains its osmoresponsiveness. The response of the DRE deletion plasmid (pLT-lacDeltaNC) to NaCl is similar to that of the undeleted plasmid.

Artificial Gene Fusion↗
PubMed1999

Osmoregulation and water balance in the springhare (Pedetes capensis).

Springhares are large rodents that live in arid and semi-arid regions of Africa. We deprived springhares of water for periods of up to 7 days to determine what physiological adaptations. If any, enable them to survive in and regions without drinking. During water deprivation, springhares lost up to 30% body weight and produced a mean maximum urine concentration of 2548 mosmol kg-1 with a maximum of 3076 mosmol kg-1 in an individual animal. Haematocrit and plasma sodium and potassium concentrations were well regulated throughout water deprivation at 47.5 +/- 3.8% and 132.6 +/- 7.4 mmol l-1 and 3.5 +/- 0.7 mmol l-1, respectively, while plasma osmolality increased slightly from 293 +/- 12.5 mosmol kg-1 to 324 +/- 7.3 mosmol kg-1. Springhares thus appeared to be good osmoregulators and were able to maintain plasma volume during 7 days of water deprivation. In addition to the production of a relatively concentrated urine, water loss was limited by the lowered solute load and faecal water loss achieved by a reduction in food consumption and by the production of very dry faeces. These abilities, together with a favourable burrow microclimate and nocturnal activity pattern, enable them to survive in arid regions.

Adaptation, Physiological↗
PubMed2002

Novel insights into the role of potassium for osmoregulation in Halomonas elongata.

The role of K(+) in osmoregulation of the halophilic bacterium Halomonas elongata was investigated. At lower salinities (0.51 M NaCl), K(+) was the predominant cytoplasmic solute (1.25 micro mol mg protein(-1)). At higher salinities (1.03 M NaCl) ectoine became the main cytoplasmic solute (1.57 micro mol mg protein(-1)), while the K(+) content remained unchanged. In response to osmotic upshock, cells of H. elongata simultaneously accumulated ectoine and K(+) glutamate. The ectoine and K(+) glutamate levels in osmotically stressed cells exceeded the level of cells adapted to high salinities. The increase in K(+) glutamate was long lasting (>120 min) and not transient, as described for non-halophiles. Regulation of the synthesis of ectoine and glutamate was proven to occur mainly at the level of enzyme activity. Limitation of K(+) inhibited the growth of salt-adapted H. elongata cells, especially at high salinities, and caused a decrease of the intracellular organic solute content, inhibition of respiration, and an abolition of the cell's ability to respond to osmotic stress. The saturation constant K(S) for K(+) was estimated to be 105 micro M at a salinity of 0.51 M NaCl, indicating that an uptake system of medium affinity is responsible for K(+) accumulation in H. elongata.

Adaptation, Physiological↗
PubMed1992

Hypothalamic osmoregulation for vasopressin release in streptozotocin-diabetic rats in vivo and in vitro.

The central osmoregulation mechanism for vasopressin (VP) release was studied in the streptozotocin diabetic (STZ-DM) rat. Electrical activities of the VP-producing cell in the supraoptic nucleus (SON) were recorded extracellularly and compared with those in the control rat both in vivo and in vitro. Neuronal activities in the periventricular area (PVA) were also recorded in the in vitro experiment. Hyperosmolar stimulation which was done with an intraperitoneal injection of 1.0 M NaCl (4 ml/kg) resulted in an increase in plasma osmolality both of STZ-DM (increased by 14 +/- 2 mOsml/kg H2O) and control rats (15 +/- 3 mOsmol/kg H2O). Increased plasma osmolality caused significant increase in the mean discharge rate of VP-producing cells in the control animals, but only an insignificant change in STZ-DM rats. In the hypothalamic slice preparations incubated in the artificial cerebrospinal fluid (301 +/- 2 mOsml/kg H2O), VP-producing cells in control rats increased their discharge rate linearly as the osmolality (310 +/- 2 and 320 +/- 1 mOsmol/kg H2O) or concentration (10(-8) and 10(-6) M) of angiotensin II (AGII) of the perfusate was increased stepwise, but there was no change in response to either stimulus in STZ-DM rats. On the other hand, there was no difference in sensitivity to osmolality and AGII of PVA neurons in both animal groups. These data indicate that lower sensibility to osmotic change of VP-producing cells in STZ-DM rats may depend, at least partially, upon the disturbance of osmo- and AGII-sensitivity in VP-producing cells themselves, and that these changes seem to be restricted to SON VP-producing cells.

Analysis of Variance↗
PubMed1992

c-fos may code for a common transcription factor within the hypothalamic neural circuits involved in osmoregulation.

Conscious rats were given an intraperitoneal (i.p.) injection of isotonic or hypertonic saline, and killed 10-240 min later. In the hypothalamus of hypertonic saline-injected rats, c-fos-mRNA positive cells were mainly restricted to the supraoptic and paraventricular nuclei and to structures associated with the lamina terminalis of the third ventricle, including in particular the subfornical organ, the organum vasculosum of the lamina terminalis (OVLT) and the median preoptic nucleus. These structures comprise the proposed anterior hypothalamic 'osmoreceptor complex' for regulation of vasopressin release. The time course of the appearance and disappearance of c-fos mRNA signals was similar in all regions. Thus c-fos protein (Fos) may be a common transcription factor in the hypothalamic neural circuits involved in osmoregulation.

Animals↗
PubMed1989

Putative role of adenohypophysis in the osmoregulation of tilapia larvae (Oreochromis mossambicus; Teleostei): an ultrastructure study.

Ultrastructure of the secretory cells in the adenohypophysis of tilapia (Oreochromis mossambicus) larvae hatched in fresh water or sea water was compared. Adenohypophysis of newly hatched larvae of tilapia is a short columnar body attached to the ventral floor of the diencephalon. The adenohypophysis is at its early differentiation stage, i.e., various types of secretory cells are still undistinguishable. Only part of the cells in the putative rostral pars distalis look like typical endocrine cells, containing well-developed rough endoplasmic reticulum, Golgi apparatus, and numerous secretory granules. The average size of secretory granules in freshwater-hatched larvae is significantly larger than those in seawater-hatched larvae (12,936 +/- 2854 nm2, N = 11 vs 3375 +/- 810 nm2, N = 10), suggesting some role of adenohypophysis in the osmoregulation of the early developmental stage of teleosts.

Animals↗
PubMed1988

Taurine in the osmoregulation of the Brattleboro rat.

The function of taurine in mammalian osmoregulation was studied in the Brattleboro rat with hereditary hypothalamic diabetes insipidus (DI). DI rats are chronically dehydrated because of their inability to synthesize vasopressin. One day of water deprivation did not affect the water balance in rats with normal vasopressin synthesis, whereas DI rats were markedly dehydrated and lost considerably body weight. Taurine content and 3H-taurine accumulation by platelets were significantly higher in DI rats, with a further increase after one day of water deprivation. In DI rats, water deprivation also evoked a clear taurine increase in skeletal muscle and in the brain. These findings indicate that taurine has an osmoregulatory function in mammals.

Animals↗
PubMed1982

Renin-angiotensin system and osmoregulation in the terrestrial chelonian Testudo hermanni Gmelin.

1. Renal renin activity, Na and K plasma urinary levels were studied in Testudo hermanni after salted diet, saline solution administration and furosemide injection. 2. Salt loading depressed renal renin activity whereas injection of the diuretic resulted in sodium loss and enhanced renal renin activity. 3. Results lead one to conclude the presence of a renin-angiotensin system with a direct action upon osmoregulation in these terrestrial chelonians.

Animals↗
PubMed1989

Respiration and osmoregulation of the estuarine crab, Rhithropanopeus harrisii (Gould): effects of the herbicide, alachlor.

1. The effects of a sudden decrease in salinity and exposure to sublethal concentrations of the herbicide, alachlor, on osmoregulation and respiration of the crab, Rithropanopeus harrisii, were studied. 2. Crabs were hyperosmotic regulators at salinities below 24 ppt and became hypoosmotic at higher salinities. Upon a salinity decrease from 20 to 1 ppt, crabs adjusted their haemolymph osmolality to a stable hyperosmotic level in 8 hr. Alachlor concentrations to 50 ppm did not affect this adjustment. 3. A salinity decrease from 10 to 0 ppt elevated VO2 and the critical oxygen tension. This response was unaffected by alachlor concentrations as high as 25 ppm.

Acetamides↗
PubMed1992

Efflux of choline and glycine betaine from osmoregulating cells of Escherichia coli.

We present evidence that glycine betaine (betaine) which was synthesized from choline was excreted and reaccumulated in osmoregulating cells of Escherichia coli. Choline which was accumulated in bet mutants defective in betaine synthesis was shown to be excreted in response to betaine uptake. Our data suggest that E. coli has efflux systems for betaine and choline which are independent of the uptake systems for these metabolites. The ProU system of E. coli, but not that of Salmonella typhimurium, can mediate low-affinity choline uptake.

Betaine↗
PubMed1989

Involvement of ion channels and active transport in osmoregulation and signaling of higher plant cells.

The transport of inorganic and organic ions across the plasma membrane and organelle membranes of higher plants by ion channels, electrogenic pumps and co-transporters is essential to vital processes such as osmoregulation, growth, development, signal transduction and the storage of solutes. Recent studies have led to the identification of specialized transport proteins in the plasma membrane and vacuolar membrane of higher plant cells. Here we have integrated the functional aspects of these membrane proteins into a model which proposes a novel basis for ion transport processes involved in the regulation of gas exchange in leaves.

Ion Channels↗
PubMed2005

The alpha-(1-->6) glycosidic linkage as a novel conformational entropic regulator in osmoregulated periplasmic alpha-cyclosophorohexadecaose.

Molecular dynamics simulations were performed to explain the conformational effect of an alpha-(1-->6)-glycosidic linkage upon the cyclic osmoregulated periplasmic glucan (OPG) produced by Xanthomonas campestris pv. citri. We suggest that a single alpha-(1-->6)-glycosidic linkage in cyclic OPG functions as a novel entropic regulator, which reduces the conformational entropy of cyclic OPG and increases the motional entropy of solvent water molecules.

Carbohydrate Conformation↗
PubMed2006

Osmoregulation and Na,K-ATPase expression in osmoregulatory organs of Scylla paramamosain.

Scylla paramamosain is a euryhaline marine crab that can actively regulate its osmotic pressure of the hemolymph. We investigated the expression of Na,K-ATPase in the osmoregulatory organs, including anterior gills, posterior gills, antennal glands, and midgut. Our cDNA sequencing of the Na,K-ATPase alpha-subunit revealed no isoforms in any of the four osmoregulatory organs studied. The full-length cDNA contains 3,866 bp that encode a complete open reading frame of 1,039 amino acids. The osmotic pressure of the hemolymph changed immediately after transference from 25 ppt to 5 and 45 ppt, and reached a new steady state within 3 days, showing the typical pattern of weak hyperosmoregulators. Expression of Na,K-ATPase alpha-subunit mRNA level was determined for individuals acclimated in 5, 25, and 45 parts per thousand (ppt) for 7 days. Compared to the mRNA level of those from 25 ppt, the level in the posterior gills from 5 ppt was significantly higher. Also, the mRNA levels in the anterior gills, posterior gills and antennal glands from 45 ppt were significantly higher than that of the respective organs in 25 ppt. This increase in the 5 ppt treatment may be responsible for the observed increase of Na,K-ATPase activity on day 14 when the posterior gills had a significantly higher activity than those in the other two salinity treatments. No difference was found in the protein level across salinities. In conclusion, the posterior gills play the most important role in osmoregulation in dilute seawater and the increase in Na,K-ATPase activity on the 7th day may be due to its gene transcription and/or mRNA translation.

Amino Acid Sequence↗
PubMed2006

Growth hormone and prolactin actions on osmoregulation and energy metabolism of gilthead sea bream (Sparus auratus).

The gilthead sea bream (Sparus auratus) is an euryhaline fish where prolactin (PRL) and growth hormone (GH) play a role in the adaptation to different environmental salinities. To find out the role of these pituitary hormones in osmoregulation and energy metabolism, fish were implanted with slow release implants of ovine GH (oGH, 5 microg g(-1) body mass) or ovine prolactin (oPRL, 5 microg g(-1) body mass), and sampled 7 days after the start of the treatment. GH increased branchial Na(+),K(+)-ATPase activity and decreased sodium levels in line with its predicted hypoosmoregulatory action. GH had metabolic effects as indicated by lowered plasma protein and lactate levels, while glucose, triglycerides and plasma cortisol levels were not affected. Also, GH changed liver glucose and lipid metabolism, stimulated branchial and renal glucose metabolism and glycolytic activity, and enhanced glycogenolysis in brain. PRL induced hypernatremia. Furthermore, this hormone decreased liver lipid oxidation potential, and increased glucose availability in kidney and brain. Both hormones have opposite osmoregulatory effects and different metabolic effects. These metabolic changes may support a role for both hormones in the control of energy metabolism in fish that could be related to the metabolic changes occurring during osmotic acclimation.

Acclimatization↗
PubMed2004

LcoP, an osmoregulated betaine/ectoine uptake system from Corynebacterium glutamicum.

In Corynebacterium glutamicum, four uptake systems for compatible solutes have been characterized so far. DHPE (DeltabetPDeltaputPDeltaproPDeltaectP), a derivative of the C. glutamicum type strain ATCC 13032 carrying deletions in the corresponding genes, still showed a low betaine uptake rate of 1.4 nmol/(min mg cdm). Genome analyses revealed the presence of a putative carrier, named low capacity osmoregulated permease (LcoP), which shows similarities to compatible solute transporters of the betaine/carnitine/choline transporter (BCCT)-family. Deletion of lcoP in DHPE resulted in betaine and ectoine uptake deficiency. LcoP, a betaine and ectoine permease is regulated at the expression and the activity level by the external osmolality. Addition of local anesthetics modulated the activity of BCCT-family members BetP, EctP, and LcoP in a different manner, indicating a different type of lipid-protein interaction.

Amino Acid Sequence↗
PubMed2004

Salt-tolerance genes involved in cation efflux and osmoregulation of Sinorhizobium fredii RT19 detected by isolation and characterization of Tn5 mutants.

Salt-tolerance genes of Sinorhizobium fredii RT19 were identified by the construction and screening of a transposon Tn5-1063 library containing over 30,000 clones. Twenty-one salt-sensitive mutants were obtained and five different genes were identified by sequencing. Eight mutants were found with disruptions in the phaA2 gene, which encodes a cation efflux system protein, while mutations in genes encoding other cation effux system proteins were found in seven (phaD2), two (phaF2) and two (phaG2) mutants. A mutation in the metH gene, encoding 5' methyltetrahydrofolate homocysteine methyltransferase, was found in two of the salt sensitive strains. Growth experiments showed that phaA2, phaD2, phaF2 and phaG2 mutants were hypersensitive to Na+/Li+ and slightly sensitive to K+ and not sensitive to sucrose and that metH mutants were highly sensitive to any of Na+, Li+, K+ and sucrose. Na+ intracellular content measurements established that phaA2, phaD2, phaF2 and phaG2 are mainly involved in the Na+ efflux in S. fredii RT19. Recovery of growth of the metH mutants incubated with different concentrations of NaCl could be obtained by additions of methionine, choline and betaine, which showed that the metH gene is probably involved in osmoregulation in S. fredii RT19.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed2005

Osmoregulation of the HtrA (DegP) protease of Escherichia coli: an Hha-H-NS complex represses HtrA expression at low osmolarity.

The HtrA protein of Escherichia coli is a heat-shock inducible periplasmic protease, essential for bacterial survival at high temperatures. Expression of htrA gene depends on the alternative factor sigmaE and on the two-component regulatory system Cpx. These regulators systems respond, among others factors, to overproduction of misfolded proteins in the periplasm or to high level synthesis of various extracytoplasmic proteins. We describe in this report the osmoregulation of the expression of htrA gene. Low osmolarity conditions result in htrA repression. We report, as well, the role of the nucleoid associated proteins H-NS and Hha in the repression of htrA expression at low osmolarity.

Bacterial Proteins↗
PubMed2004

Structural analysis of Escherichia coli OpgG, a protein required for the biosynthesis of osmoregulated periplasmic glucans.

Osmoregulated periplasmic glucans (OPGs) G protein (OpgG) is required for OPGs biosynthesis. OPGs from Escherichia coli are branched glucans, with a backbone of beta-1,2 glucose units and with branches attached by beta-1,6 linkages. In Proteobacteria, OPGs are involved in osmoprotection, biofilm formation, virulence and resistance to antibiotics. Despite their important biological implications, enzymes synthesizing OPGs are poorly characterized. Here, we report the 2.5 A crystal structure of OpgG from E.coli. The structure was solved using a selenemethionine derivative of OpgG and the multiple anomalous diffraction method (MAD). The protein is composed of two beta-sandwich domains connected by one turn of 3(10) helix. The N-terminal domain (residues 22-388) displays a 25-stranded beta-sandwich fold found in several carbohydrate-related proteins. It exhibits a large cleft comprising many aromatic and acidic residues. This putative binding site shares some similarities with enzymes such as galactose mutarotase and glucodextranase, suggesting a potential catalytic role for this domain in OPG synthesis. On the other hand, the C-terminal domain (residues 401-512) has a seven-stranded immunoglobulin-like beta-sandwich fold, found in many proteins where it is mainly implicated in interactions with other molecules. The structural data suggest that OpgG is an OPG branching enzyme in which the catalytic activity is located in the large N-terminal domain and controlled via the smaller C-terminal domain.

Amino Acid Sequence↗