Disaccharides as a new class of nonaccumulated osmoprotectants for Sinorhizobium meliloti.
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Sucrose and ectoine (1,4,5,6-tetrahydro-2-methyl-4-pyrimidine carboxylic acid) are very unusual osmoprotectants for Sinorhizobium meliloti because these compounds, unlike other bacterial osmoprotectants, do not accumulate as cytosolic osmolytes in salt-stressed S. meliloti cells. Here, we show that, in fact, sucrose and ectoine belong to a new family of nonaccumulated sinorhizobial osmoprotectants which also comprises the following six disaccharides: trehalose, maltose, cellobiose, gentiobiose, turanose, and palatinose. Also, several of these disaccharides were very effective exogenous osmoprotectants for strains of Rhizobium leguminosarum biovars phaseoli and trifolii. Sucrose and trehalose are synthesized as endogenous osmolytes in various bacteria, but the other five disaccharides had never been implicated before in osmoregulation in any organism. All of the disaccharides that acted as powerful osmoprotectants in S. meliloti and R. leguminosarum also acted as very effective competitors of [14C]sucrose uptake in salt-stressed cultures of these bacteria. Conversely, disaccharides that were not osmoprotective for S. meliloti and R. leguminosarum did not inhibit sucrose uptake in these bacteria. Hence, disaccharide osmoprotectants apparently shared the same uptake routes in these bacteria. Natural-abundance 13C nuclear magnetic resonance spectroscopy and quantification of cytosolic solutes demonstrated that the novel disaccharide osmoprotectants were not accumulated to osmotically significant levels in salt-stressed S. meliloti cells; rather, these compounds, like sucrose and ectoine, were catabolized during early exponential growth, and contributed indirectly to enhance the cytosolic levels of two endogenously synthesized osmolytes, glutamate and the dipeptide N-acetylglutaminylglutamine amide. The ecological implication of the use of these disaccharides as osmoprotectants is discussed. (+info)
Exchanges of sodium and chloride at low salinities by Nereis diversicolor (Annelida, Polychaeta).
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1. Experiments to compare the exchange (total influx) of sodium and chloride in the polychaete Nereis diversicolor in steady-state adaptation to very low salinities are reported. 2. The Na-uptake mechanism shows a high affinity for sodium, reaching half the maximal uptake rate at an external Na-concentration of 8-10 mM/liter (ca. 2% SW), and becomes "saturated" or reaches a plateau of uptake at concentrations of 40-50 mM/liter (ca. 10% SW) up to ca. 350 mM/liter (75% SW), above which Na-exchange is proportional to the external concentration. 3. The Cl-uptake curve differs from the Na-uptake curve in showing a relative depression at very low salinities before reaching "saturation" at Cl-concentrations of 50-60 mM/liter (ca. 10% SW). Cl-uptake becomes proportional to external concentration in salinities of 50% SW or greater, suggestive of passive diffusion in the ionic and osmotic conforming range. 4. It is shown that the permeability of the body wall, both to Na and to Cl, is reduced at very low salinities, thus destroying one of the assumptions upon which a previously-presented balance-sheet for chloride exchanges in N. diversicolor was based (Smith, 1970a). 5. Attempts to demonstrate an activation of the Na-uptake mechanism at very low salinities were inconclusive; reduction of body-wall permeability to sodium masks any possible activation. 6. It is suggested that the inside-negative body-wall potential is related to the depression of the Cl-uptake curve in salinities below 10% SW. (+info)
Osmotic adjustment in an estuarine population of Urosalpinx cinerea (Say, 1822) (Muricidae, Gastropoda).
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Individuals from a subtidal, estuarine population of the common oyster drill, Urosalpinx cinerea (Say, 1822), were brought into the laboratory and tested for osmotic adjustment to changing salinity. Tissue variables monitored at seven experimental salinities ranging from 10 to 40% were tissue fluid osmolality, chloride, sodium, potassium, free amino acids (FAA), ninhydrin-positive substances (NPS) and water content. The results of this study demonstrate that the test animals did not exhibit anisosmotic regulation at any of the experimental salinities. However, the data do suggest a high degree of hyper-ionic regulation of potassium at all experimental salinities and a hyporegulation of sodium between the 25 and 40% salinities. Taurine, aspartic acid, alanine and glycine were the four FAA present in relatively consistent high amounts. These four amino acids comprised from 59.6 to 75.7% of the total FAA pools. It is postulated that the population does not maintain its euryhaline survival status through an osmoregulatory mechanism. Rather, the population has probably adapted physiologically to withstand dilution of its body fluids during spring conditions of low salinities. (+info)
Effect of prolonged administration of a urinary kinase inhibitor, ebelactone B on the development of deoxycorticosterone acetate-salt hypertension in rats.
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The effect of prolonged administration of a carboxypeptidase Y-like kininase inhibitor, ebelactone B (EB) (2-ethyl-3, 11-dihydroxy-4, 6, 8, 10, 12-pentamethyl-9-oxo-6-tetradecenoic 1, 3-lactone), on the development of deoxycorticosterone acetate (DOCA)-salt hypertension was tested. The systolic blood pressure (SBP) of non-treated 6-week-old Sprague-Dawley strain rats was gradually increased by DOCA-salt treatment from 137+/-2 mmHg (n=11) to 195+/-7 mmHg at 10 weeks of age. With daily oral administration of lisinopril (5 mg kg(-1), twice a day), which is an inhibitor of angiotensin converting enzyme, a major kininase in plasma, the development of hypertension was not suppressed. By contrast, administration of EB (5 mg kg(-1), twice a day), completely inhibited the development of hypertension (SBP: 146+/-1 mmHg, n=5, 10 weeks old). The reduced SBP at 10 weeks of age was equal to the SBP before any treatment (142+/-1 mmHg, n=5). Direct determination of mean blood pressure (MBP) in conscious, unrestrained rats confirmed that MBP elevation was completely inhibited by EB. Continuous subcutaneous infusion (5 mg kg(-1) day(-1)) of HOE140, a bradykinin B2 receptor antagonist, restored the elevation of SBP, which was suppressed by EB. The weights of left ventricle of DOCA-salt treated rats 10-weeks-old (0.36+/-0.02 g 100 g body weight(-1), n=11) was significantly reduced by EB (0.27+/-0.01, n=5), as were the sodium levels in serum, cerebrospinal fluid and erythrocyte. These findings suggested that EB is effective in preventing salt-related hypertension presumably by eliminating sodium retention. (+info)
Intracellular pH regulation by HCO3-/Cl- exchange is activated during early mouse zygote development.
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We report here that at least one major pHi-regulatory mechanism, the HCO3-/Cl- exchanger, is quiescent in unfertilized mouse eggs but becomes fully activated during early development following fertilization. Zygotes (8-12 h postfertilization) exhibited a marked intracellular alkalinization upon external Cl- removal, which is indicative of active HCO3-/Cl- exchangers, in contrast to the very small response observed in eggs. In addition, efflux of Cl- from eggs upon external Cl- removal was much slower than that from zygotes, indicating additional pathways for Cl- to cross the plasma membrane in zygotes. Furthermore, while zygotes quickly recovered from an induced alkalosis, eggs exhibited only a slow, incomplete recovery. Following in vitro fertilization (IVF), increased HCO3-/Cl- exchanger activity was first detectable about 4 h postfertilization and reached the maximal level after about 8 h. The upregulation of HCO3-/Cl- exchanger activity after fertilization appeared to occur by activation of existing, inactive exchangers rather than by synthesis or transport of new exchangers, as the increase in activity following IVF was unaffected by inhibition of protein synthesis or by disruption of the Golgi apparatus or the cytoskeleton. This activation may depend on the Ca2+ transients which follow fertilization, as suppression of these transients, using the Ca2+ chelator BAPTA, reduced subsequent upregulation of HCO3-/Cl- exchanger activity by about 50%. Activation of pHi-regulatory systems may be a widespread feature of the earliest period of embryonic development, not restricted to species such as marine invertebrates as previously believed. (+info)
EnvZ-independent phosphotransfer signaling pathway of the OmpR-mediated osmoregulatory expression of OmpC and OmpF in Escherichia coli.
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The Escherichia coli EnvZ-OmpR regulatory system is a paradigm of intracellular signal transduction mediated by the well-documented phosphotransfer mechanism, by which the expression of the major outer membrane proteins, OmpC and OmpF, is regulated in response to the medium osmolarity. Although it is clear that the EnvZ histidine(His)-kinase is the major player in the phosphorylation of OmpR, it has been assumed for some time that there may be an alternative phospho-donor(s) that can phosphorylate OmpR under certain in vitro and in vivo conditions. In this study, to address this long-standing issue, extensive genetic studies were done with certain mutant alleles, including delta envZ, delta(ackA-pta), and delta sixA, as well as delta ompR. Here, for the first time, genetic evidence is provided that, in addition to EnvZ, acetyl phosphate and an as yet unidentified sensor His-kinase can serve as alternative in vivo phospho-donors for OmpR, even in the envZ+ background. A model for the alternative phosphotransfer signaling pathway involved in the phosphorylation of OmpR is proposed. (+info)
Is the primitive regulation of pituitary prolactin (tPRL177 and tPRL188) secretion and gene expression in the euryhaline tilapia (Oreochromis mossambicus) hypothalamic or environmental?
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We examined the effects of environmental salinity on circulating levels of the two prolactins (tPRL177 and tPRL188) and levels of pituitary tPRL177 and tPRL188 mRNA in the euryhaline tilapia, Oreochromis mossambicus. Fish were sham-operated or hypophysectomized and the rostral pars distalis (RPD) autotransplanted onto the optic nerve. Following post-operative recovery in (1/4) seawater, tilapia were transferred to fresh water (FW), (1/4) seawater (SW) or SW. Serum tPRL177 and tPRL188 levels in sham-operated and RPD-autotransplanted fish were highest in FW and decreased as salinity was increased. tPRL177 and tPRL188 mRNA levels in RPD implants as well as in pituitaries from the sham-operated fish were also highest in FW and decreased with increasing salinity. Serum osmolality increased with salinity, with the highest levels occurring in the seawater groups. We conclude that some plasma factor (probably plasma osmolality), in the absence of hypothalamic innervation, exerts a direct regulatory action on prolactin release and gene expression in the pituitary of O. mossambicus. This regulation is in accord with the actions of the two prolactins in the freshwater osmoregulation of the tilapia. (+info)
Characterization of a Na+-dependent betaine transporter with Cl- channel properties in squid motor neurons.
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Most marine invertebrates, including squids, use transporters to accumulate organic osmolytes such as betaine, to prevent water loss when exposed to elevated salinity. Although a limited number of flux studies have shown the Na+ dependence of betaine transport, nothing is known about the electrogenic properties of osmolyte transporters. We used whole cell and perforated-patch voltage-clamp techniques to characterize the electrical properties of the betaine transporter in giant fiber lobe motor neurons of the squid Lolliguncula brevis. Betaine activated a large, Cl--selective current that was reversibly blocked by 100 microM niflumic acid (97 +/- 2% block after 40 s, SD; n = 7) and partially inhibited by 500 microM SITS (29 +/- 11%; n = 5). The Cl- current was Na+ dependent and was virtually eliminated by isotonic replacement of Na+ with Li+, NMDG+, or Tris+. Concentration-response data revealed an EC50 in a physiologically relevant range for these animals of 5.1 +/- 0.9 mM (n = 11). In vertebrates, the betaine transporter is structurally related to the GABA transporter, and although GABA did not directly activate the betaine-induced current, it reversibly reduced betaine responses by 34 +/- 14% (n = 8). Short-term changes in osmolality alone did not activate the Cl- current, but when combined with betaine, Cl- currents increased in hypertonic solutions and decreased in hypotonic solutions. Activation of the betaine transporter and Cl- current in hypertonic conditions may affect both volume regulation and excitability in L. brevis motor neurons. This study is the first report of a novel betaine transporter in neurons that can act as a Cl- channel. (+info)