Acid exposure in euryhaline environments: ion regulation and acid tolerance in larval and adult Artemia franciscana

Mortality, and whole-body levels of [Na], [Cl] and [K]were measured in adult and naupliar stages of Brine Shrimp, Artemia franciscana, after 24h exposure to a waters of a range of acid (H₂SO₄)concentrations (pH 8.3 to 4.5). Acid effects were tested in both dilute (20%) and full strength artificial seawater (ASW). All stages showed high sensitivity to acid stress whether tested in 20% or100% ASW. Nauplii were more sensitive than adults in either medium. Mortality in each case was correlated with dramatic changes in whole body [Na] and [Cll but animals in 20% ASW lost [Na] and [Cl] to the environment while animals in 100% ASW gained them from the environment. Clearly animals which ion-regulate in euryhaline media are more sensitive than expected to acid stress which may thus pose a serious threat to sensitive euryhaline habitats. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ionoregulatory physiology of two species of African lungfishes Protopterus dolloi and Protopterus annectens

Basic ionoregulatory physiology was characterized in two species of African lungfish, slender African lungfish Protopterus dolloi and West African lungfish Protopterus annectens , largely under aquatic conditions. There were no substantive differences between the two species. Plasma [Na], [Cl] and [Ca] were only 60–80% of those typical of freshwater teleosts, and plasma Ca activity was particularly low. Unidirectional Na and Cl influx rates from water were also very low, only c . 10% of teleost values, whereas unidirectional Ca influx rates were comparable with teleost rates. Protopterus spp. were fed a 3% ration of bloodworms every 48 h. The bloodworm diet provided similar amounts of Na and Ca as uptake from water, but almost no Cl. Efflux rates of Na and Cl through the urine were greater than via the faeces, whereas the opposite was true for Ca. Net ion flux measurements and ionic balance sheet calculations indicated that (1) both water and dietary uptake routes are important for Na and Ca acquisition; (2) the waterborne route predominates for Cl uptake; (3) unidirectional ion effluxes across the body surface (gills and skin) rather than urine and faeces are the major routes of loss for Na, Cl and Ca. Tissues (muscle, liver, lung, kidney, intestine and heart) and plasma ions were also examined in P. dolloi 'terrestrialized' in air for up to 5 months, during which plasma ion concentrations (Na, Cl, Ca and Mg) did not change and there were only a few alterations in tissue ions, that is, increased [Na] in intestine, decreased [Cl] in kidney and increased [Ca] in liver and kidney.     

Electron probe X-ray microanalysis of cellular ions in the eccrine secretory coil cells during methacholine stimulation

Summary Intracellular concentrations of Na, K, Cl ([Na], [K] and [Cl], respectively) and other elements were determined in isolated monkey eccrine sweat secretory coil cells using quantitative electron probe X-ray microanalysis of freeze dried cryosections. The validity of the methodology was partially supported by qualitative agreement of the X-ray microanalysis data with those obtained by micro-titration with a helium glow spectrophotometer. [Na], [K] and [Cl] of the cytoplasm were the same as those in the nucleus in both clear and dark cells. [Na], [K], and [Cl] of the clear cells were also the same as those of the dark cells at rest and after stimulation with methacholine (MCh), suggesting that these two cell types behave like a functional syncytium. MCh stimulation induced a pharmacologically specific, dose-dependent decrease in [K] and [Cl] (as much as 65%), and a 3.7-fold increase in [Na]. In myoepithelial cells, a similar change in [Na] and [K] was noted after MCh stimulation although the decrease in [Cl] was only 20%. The MCh-induced change in [Na], [K] and [Cl] was almost completely inhibited by removal of Ca²⁺ from the medium. 10^–4 m bumetanide inhibited the MCh-induced increase in [Na], reduced the decrease in [K] by about 50%, but slightly augmented the MCh-induced decrease in [Cl]. 10^–4 m ouabain increased [Na] and decreased [K] as did MCh; however, unlike MCh, ouabain increased [Cl] by 56% after 30 min of incubation. Thus the data may be best interpreted to indicate that Ca-dependent K efflux and (perhaps also Ca-dependent) Cl efflux are the predominat initial ionic movement in muscarinic cholinergic stimulation of the eccrine sweat secretory coils and that the ouabain-sensitive Na pump plays an important role in maintenance of intracellular ions and sweat secretion.     

The effects of salt depletion on blood and tissue ion concentrations in the freshwater mussel,Ligumia subrostrata (Say)

Summary The extracellular and intracellular fluid volumes of pondwater acclimatedLigumia subrostrata are equal (3.9 ml/g dry tissue). Total blood solute is 47 mOsm and is composed primarily of Na (19.1 mM), Cl (10.6 mM), HCO₃ (12.7 mM), Ca (4.3 mM), and K (0.5 mM). Major intracellular solutes are K (14.0 mM), Na (7.0 mM) and Cl (2.4 mM).L. subrostrata continuously exposed to deionized water at 20°C exhibit a maximum decrease of 23% in extracellular fluid total solute within 30 days. The maximum [Na] and [Cl] losses are 40% and 76% respectively, while [Ca] and [HCO₃] increase by 44% and 37% respectively. No apparent change in extracellular [K] occurs. Intracellular [Na] decreases 53% and [Cl] decreases 79%, but [K] declines only 15%. Intracellular fluid volume, extracellular fluid volume, and total body water decrease 17%, 31%, and 22% respectively. Inulin clearance is 0.41 ml/g dry tissue·h for pondwater acclimated mussels and declines to 0.24 ml/g dry tissue·h during salt depletion. When salt depleted mussels are returned to solutions containing Na or Cl, they experience a net uptake of salt. The accumulated ions are about equally distributed in the extra- and intracellular compartments.     

Embryonic and larval development of brown trout, Salmo trutta L.: exposure to aluminium, copper, lead or zinc in soft, acid water

Freshly fertilized ova, eyed ova and yolk-sac fry of brown trout, Salmo trutta L., were exposed to each of four trace metals (aluminium: 6000 nmol l^?1; copper: 80 nmol l^?1; lead: 50 nmol l^?1; zinc: 300 nmol l^?1) while held in flowing artificial soft-water media maintained at pH 4.5 or 5.6 and [Ca] 20 or 200 μmol l^?1. In continuous exposure from fertilization, survival of ova was severely affected at pH 4.5 and [Ca] 20 μmol l^?1, regardless of the presence of Cu, Pb or Zn; Al reduced embryonic mortality and improved hatching success. High ambient [Ca] at pH 4.5 increased egg survival. At ‘swim-up’, surviving fry exposed to Al or Pb had lower whole body Ca, Na and K content, irrespective of pH or ambient [Ca]. Cu reduced whole body Ca and K content at pH 5.6 and [Ca] 200 μmol^?1, and whole body Ca, Na and K content in the other media. Zn reduced whole body mineral content at pH 5.6 and [Ca] 20 μmol l^?1. Whole body Mg content was reduced by all trace metals at pH 5.6 and [Ca] 20 μmol l^?1, and by Cu at pH 5.6 and [Ca] 200 μmol l^?1. Al and Cu impaired skeletal calcification at pH 5.6 at both ambient [Ca]; Pb only at [Ca] 20 μmol I^?1. Zn enhanced calcification at pH 4.5 and [Ca] 200 μmol l^?1. In the absence of trace metals, low pH reduced body Ca, Na, K content and skeletal calcification at [Ca] 200 μmol l^?1. The uptake of Ca, Na and K, measured at regular intervals from hatching was impaired to the same extent by all treatments at pH 4.5, irrespective of ambient [Ca] or trace metal presence. At pH 5.6, irrespective of ambient [Ca], Al, Cu and Pb impaired Ca and K uptake. The rate of Na uptake was reduced by Al and Cu. Al-treated yolk-sac fry, exposed to low ambient [Ca] from 200–300° days post-hatch, suffered high mortalities regardless of pH. Ca, Na and K uptake was impaired by all treatments at pH 4.5, and by Al and Cu at pH 5.6 in a similar exposure period. The development of the early stages of brown trout in the presence of trace metals is discussed in relation to recruitment failure in areas of soft, acid water.     

Lowering extracellular sodium or pH raises intracellular calcium in gastric cells

Summary The dependence of cytoplasmic free [Ca] (Ca _i ) on [Na] and pH was assessed in individual parietal cells of intact rabbit gastric glands by microfluorimetry of fura-2. Lowering extracellular [Na] (Na _o ) to 20mm or below caused a biphasic Ca _i increase which consisted of both release of intracellular Ca stores and Ca entry across the plasma membrane. The Ca increase was not blocked by antagonists of Ca-mobilizing receptors (atropine or cimetidine) and was independent of the replacement cation. Experiments in Ca-free media and in Na-depleted cells indicated that neither phase was due to reversal of Na/Ca exchange. The steep dependence of the Ca _i increase on Na _o suggested that the response was not due to lowering intracellular [Na] (Na _i ). The effects of low Na _o on Ca _i were also completely independent of changes in intracellular pH (pH _i ). Ca _i was remarkably stable during changes of pH _i of up to 2 pH units, indicating that H and Ca do not share a cytoplasmic buffer system. Such large pH excursions required determination of the pH dependence of fura-2. Because fura-2 was found to decrease its affinity for Ca as pH decreased below 6.7, corrections were applied to experiments in which large pH _i changes were observed. In contrast to the relative insensitivity of Ca _i to changes in pH _i , decreasing extracellular pH (pH _o ) to 6.0 or below was found to stimulate release of intracellular Ca stores. Increased Ca entry was not observed in this case. The ability of decreases in Na _o and pH _o to stimulate release of intracellular Ca stores suggest interactions between Na and H with extracellular receptors.     

Distribution of potassium and chloride permeability over the surface and T-tubule membranes of mammalian skeletal muscle

Summary The distribution of K and Cl permeability,P _K andP _Cl, over the surface and T-tubule membranes of red rat sternomastoid fibers has been determined. Membrane potential,V _m, was recorded with 3-m KCl-filled glass microelectrodes. Changes inV _m with changes in [K]_o or [Cl]_o were used to estimateP _Cl/P _K in normal and detubulated preparations. The results show that the T-tubule membrane has a highP _Cl and is therefore different from the T-tubule membrane of amphibian fibers. Analysis of the time course of depolarization when [K]_o was raised (in SO₄ solutions) showed thatP _K was distributed over the surface and T-tubule membranes. Two observations suggested that T-tubuleP _Cl was higher than the surfaceP _Cl. Firstly, in normal fibers, the depolarization caused by an increase in [K]_o was 3.5 times greater in SO₄ solutions than in Cl solutions. In marked contrast, the depolarization in glycerol-treated fibers was independent of [Cl]_o. Secondly, the rapid change inV _m when [Cl]_o was changed was reduced by 80% after glycerol treatment. Both observations suggest thatP _Cl was low in glycerol-treated fibers.P _Cl/P _K was calculated from theV _m data using Goldman, Hodgkin and Katz equations for Na and K or for Na, K, and Cl. In normal fibersP _Cl/P _K=4.5 and in glycerol-treated fibersP _Cl/P _K=0.28. Since it is unlikely that glycerol treatment would increaseP _K, the reduction in the ratio must follow the loss of Cl permeability channels in the T-tubule membrane.     

Na and Cl transport and short-circuit current in rabbit ileum

Summary Na and Cl fluxes and short-circuit current (I _sc) in rabbit ileum have been studied as a function of ionic concentrations in HCO₃-free solutions. Both net Na flux (J _net ^Na ) andI _sc show similar saturation functions of [Na] at fixed [Cl]. They show no significant difference between zero and 112mm Na but at 140mm NaI _sc is significantly greater than theJ _net ^Na . Net Cl transport, secretion, is observed only at 140mm Na and is approximately equivalent to the difference between theI _sc andJ _net ^Na . The transcellular mucosa-to-serosa Na fluxes measured at 140 and 70mm Na do not differ significantly from the correspondingI _sc. The net Cl flux varies with [Cl] at fixed [Na] whileI _sc is virtually not affected by [Cl]. These results suggest that the absorptive Na transport process is electrogenic and responsible for theI _sc and that the secretory fluxes of Na and Cl are coupled, require high [Na], vary with [Cl], and do not contribute toI _sc. K-free solution abolishes theI _sc after a prolonged lag. Finally, the effect of a low resistance shunt pathway on active Na absorption is examined with a four-compartment model.Deceased (October 16, 1974).     

Cat Heart Muscle In Vitro : IV. Inhibition of transport in quiescent muscles

Cellular concentrations, [K]_i, [Na]_i, and [Cl]_i, and cell water contents were measured in vitro at 27°C in cat papillary muscles. Measurements were made with and without ouabain at varying concentrations of K and ouabain, at pH 5.2 and 9.0, in absence of O₂, and in NaCl-free solution. Large losses of cell K and increases of cell Na occurred in presence of ouabain, at 2–3°C, and in K-free medium. The dependence of inhibition of cation transport by ouabain on external K concentration, studied at constant initial [K]_i, was consistent with a competition between K and ouabain localized to the external face of the membrane. In NaCl-free sucrose solution [K]_i remained at its physiological value and was not affected by exposure to ouabain or low temperature, except when Ca was also omitted. Ouabain inhibition persisted at pH 9.0 and in Ca-poor media. Cells swelled and lost K at pH 5.2, and residual ouabain effect was small. At pH 9.0, or in absence of O₂, or in Ca-poor solutions cells became permeable to mannitol. The ion movements observed after inhibition of active transport are compatible either with a passive K distribution and a primary inhibition of Na extrusion or with inhibition of a coupled active transport of both K and Na.     

Differences in low pH tolerance among closely related sunfish of the genus Enneacanthus

Synopsis Three closely related sunfish in the genus Enneacanthus were examined to determine if differences existed in their tolerance to low pH that could explain their contrasting distributions. Na fluxes of E. obesus, E. gloriosus, and E. chaetodon were measured during 12 h exposure to pH 4.0 and 3.5 (all species), and 3.25 (former 2 species only). All experienced ionic disturbances upon acid exposure resulting from inhibition of active Na influx and stimulation of passive Na efflux, but E. gloriosus and E. chaetodon experienced greater disturbances than E. obesus at all pH's tested. Body and plasma Na concentrations of E. gloriosus were measured after one week of exposure to a range of pH's for comparison with previously published data from E. obesus. Exposure to pH 4.0 and below caused a depression in body and plasma Na concentration of E. gloriosus, and only two of 10 fish survived the one week test period at pH 3.5; none survived at pH 3.25. In contrast, exposure to pH 4.0 for five weeks had no effect on body Na concentration of E. obesus, all 10 fish survived exposure to pH 3.5 for two weeks. Growth of E. gloriosus and E. obesus were measured separately during 12 weeks of exposure to a range of pH's. E. gloriosus exposed to pH 4.25 and 4.0 grew at a lower rate than those at higher pH's (4.5, 5.0, and 5.8), and body Na concentrations of fish at pH's 4.25 and 4.0 were significantly less than the others. With declining pH E. obesus did not exhibit reduced growth until pH 3.75 was reached; no depression in body Na concentration occurred at this pH. These results show that there are marked differences in low pH tolerance among closely related species of Enneacanthus which could affect their distributions and competitive interactions.     

Effects of acidic pH on predation rates and survivorship of damselfly nymphs

Environmental variables such as pH critically affect the physiology and ecology of aquatic organisms. Our lack of information regarding indirect effects of acid precipitation requires investigation of acid stress and response to acid stress by species of freshwater communities. Damselfly nymphs Enallagma civile (Odonata: Coenagrionidae) are abundant aquatic predators and food items for other secondary consumers.We investigated the effects of low pH on mortality, survivorship, predation rate, respiration rate, and caloric content of nymphs of E. civile. We hypothesized that acid stress would increase mortality and decrease predation rate among surviving individuals. We hypothesized that respiration rate and caloric content as measures of physiological condition would decrease in acid-stress conditions.We cultured individual early-instar nymphs in the laboratory with a controlled diet of mosquito larvae. The nymphs were reared to final instar in pond water and artificially reconstituted soft water (RSW) adjusted to pH 3.5, 4.5, 5.5, and ambient conditions of the collection site.Predation rate was significantly lower in RSW than in pond water in treatments of equivalent H⁺ concentrations. This indicated stress from differences in dissolved solids in RSW compared with pond water. Acid conditions significantly affected predation rates in pond water, but only at pH 3.5 and only for the largest instar. Mortality increased and survivorship decreased at low pH. Early-instar mortality and survivorship were particularly susceptible to acid stress. Treatments of pH 4.5, 5.5 and ambient did not significantly alter respiration rate or caloric content. However, respiration rate and caloric content increased at pH 3.5.Damselfly nymphs tolerated pHs as low as 4.5 without significant changes (including predation rate). However, the effects of pH 3.5 were significant and greatly lowered the predation and fitness of the nymphs.author for correspondence     

Water and solute regulation in Procephalothrix spiralis Coe and Clitellio arenarius (Müller) III. Long-term acclimation to diluted seawaters and effect of putative neuroendocrine structures

When acutely transferred to diluted seawater (SW), Procephalothrix spiralis and Clitellio arenarius regulate water content (g H₂O/g solute free dry wt = s.f.d.w.) via loss of Na and Cl (µmoles/g.s.f.d.w.). The present study extends these observations to a greater range of salinities and determines the effects of long-term, stepwise acclimation to diluted seawaters. Final exposure to a given experimental seawater (70, 50, 30, 15%) was 48 hours. Osmolality (mOsm/kg H₂O) and Na, K, and Cl ion concentrations (mEq/l) were determined in total tissue water and in the extracellular fluid of C. arenarius. Extracellular volume was determined as the ¹⁴C-polyethylene glycol space. Both species behaved as hyperosmotic conformers in diluted seawaters. However, reduction of the osmotic gradient between worm and medium occurred in P. spiralis, but not C. arenarius, in 30 and 15% SW. In both species, osmolality and Na, Cl, and K concentrations in total tissue water decreased with increased dilution of the SW. Water content increased with dilution of the medium but was lower than that which would be predicted based on approximation of the van't Hoff relation. This indicated the occurrence of regulatory volume decrease (RVD). In P. spiralis, in 70 or 50% SW, RVD was accompanied by loss of Na and Cl contents. However, in 30 or 15% SW, Na and Cl contents increased and in worms in 15% SW K content decreased. The latter movements of Na, Cl and K are indicative of cellular hysteresis and were associated with decreased viability, indicating the lower limits of regulatory ability in this species. In comparison, RVD in C. arenarius occurred in all diluted seawaters and was accompanied by loss of Na and Cl contents. In C. arenarius, evidence for reduced viability was absent. Removal of the supra- and subesophageal ganglia of C. arenarius resulted in retention of water, Na and Cl (g H₂O or µmoles/g s.f.d.w.) in worms acclimated to 70% SW. Removal of the cerebral ganglia and cephalic glands of P. spiralis did not significantly influence regulation of water content.     

Villus and Crypt Cell Composition in the Secreting Mouse Jejunum Measured with X-ray Microanalysis

The response of the villus and crypt cells of the mouse jejunum to secretagogues has been assessed through measurements of cellular composition with x-ray microanalysis. In nonstimulated tissues the Na concentration ([Na]c) of the crypt cells was significantly less, and the K ([K]c) and Cl ([Cl]c) concentrations were significantly greater, than that of the villus cells. There was also a decreasing gradient of [Na]c and increasing gradient of [K]c from the villus tip to crypt base due to a greater number of cells with a high [Na]c and low [K]c in the upper regions of the villi. Theophylline (10 mmol L⁻¹) stimulated a sustained increase in bumetanide sensitive short circuit current (Isc) and significantly decreased the [Na]c of the villus cells. Similar, but smaller changes were seen in the crypt cells. Changes in villus cell [Na]c reflected a reduction in the number of cells with a high [Na]c. Inhibition of the apical Na/H exchanger (1 mmol L⁻¹ amiloride) had little effect on basal Isc and the subsequent addition of theophylline increased Isc to a comparable extent as seen without amiloride. However, after amiloride treatment the only change in cellular composition was a reduction in the [Cl]c of both crypt and villus cells, suggesting that both regions are involved in the secretory response. These data suggest that the dominant response of the jejunum to secretagogues is an inhibition of Na absorption via Na/H exchange in the villi and the secretory response is distributed throughout the crypt/villus axis. Received: 1 July 1997/Revised: 4 November 1997     

The relationship between mitogen-induced changes in the cytoplasmic pH and free Ca2+ concentration in rat thymocytes

The relationship between pHi and [Ca]i signals generated in rat thymocytes by the mitogen Con A has been investigated. It is shown that the mitogen-induced [Ca]i rise is dependent on Na+/H+ exchange or some other Na(+)-sensitive process. This conclusion is based on the following findings: (i) [Ca]i response to Con A weakens upon decreasing the concentration of extracellular Na+, or inhibiting Na+/H+ exchange; (ii) agents that alkalinize the cytoplasm (the phorbol ester TPA, the Na+/H+ ionophore monensin and NH4Cl) cause an increase in [Ca]i (Klip, A., Rothstein, A. and Mack, E. (1984) Biochem. Biophys. Res. Commun. 124, 14-22; Grinstein, S. and Goetz, J.D. (1985) Biochim. Biophys. Acta 819, 267-270); (iii) The effects of Con A, TPA and monensin on [Ca]i are not additive. The last observation suggests that all these agents activate the same Na+/H+ (Na+ and/or H+)-dependent system of Ca2+ transport. It is found that the pH i and [Ca]i responses in rat thymocytes are sensitive to changes in the intracellular levels of cyclic nucleotides, ATP and in temperature. These regulatory effects on the ionic signals are different for Con A, TPA and monensin. In particular, both the stimulation of Na+/H+ antiport and the [Ca]i rise brought about by Con A or TPA are inhibited upon elevating the cellular cAMP. In contrast, the monensin-induced [Ca]i signal is almost independent of cAMP but is highly sensitive to changes in cGMP and temperature. Reducing the ATP level eliminates both the pHi and [Ca]i responses to Con A but not to monensin. These different characteristics of [Ca]i signals elicited by the mitogen and the Na+/H+ ionophore indicate that these agents use different mechanisms to activate the Na+/H(+)-dependent Ca2+ transporting system. A [Ca]i response to monensin has been obtained in some other cell types, namely, in lymphoblastoid Raji cells, Ehrlich ascites tumor cells and also in platelets.     

The Role of Calcium in the Regulation of the Steady-State Levels of Sodium and Potassium in the HeLa Cell

Studies on HeLa cells in spinner culture at pH 7.0 and 37° have shown that [Na]_i decreased and [K]_i increased with increasing [Ca]_o. In Na-free (choline) medium [K]_i remained high whether or not Ca was present in the medium. [Na]_i and [K]_i approached a new steady state within 1 min after transfer to Ca-free medium and returned to the initial values within 15 min upon readdition of Ca. 40% of the cell Ca exchanged within 1 min followed by a slow exchange of the remaining Ca over several hours. [Ca]_i increased with decreasing [Na]_o but was independent of [K]_o. Equimolar Mg did not substitute for Ca in maintaining low [Na]_i and high [K]_i. Under steady-state conditions about 50% of the cell Na exchanged in accordance with a single rate constant. The initial Na influx was 270, 100, and 2.5 µM/liter of cell water/sec for 0, 0.10, and 1.0 mM [Ca]_o, respectively. When Na transport was inhibited with strophanthidin and [Na]_i and [K]_i allowed to reach a steady state, Na influx was more rapid for cells incubated in Ca-free medium than for cells incubated in medium containing 1.0 mM Ca. These results suggest that Ca competes with Na at the cell membrane and thus controls the passive diffusion of Na into the cell.     

Membrane permeability changes in amphibian eggs at ovulation

Electropotential differences between the cytoplasm and external medium have been compared in the mature R. pipiens occyte and the ovulated unfertilized egg as a function of [Na]_o, [K]_o, [Ca]_o and [Cl]_o. In solutions containing 1.0 mM Ca⁺⁺ the oocyte behaved as though it were predominantly permeable to K⁺ and Cl^?, i.e., like a KCl electrode. However, the steady potential decreased with decreasing [Ca]_o and in 5 × 10^?4 mM [Ca]_o the oocyte membrane behaved like a NaCl electrode. Studies on the steady potential as a function of [Na]_o, [K]_o and [Cl]_o in 1.0 mM Ca⁺⁺ or Ca-free solutions suggest that Ca⁺⁺ controls the passive permeability of the oocyte membrane to Na⁺ and Cl^?. In the ovulated unfertilized egg the K⁺ selectivity of the cell membrane disappeared and the system behaved like a NaCl electrode. No effect of external Ca⁺⁺ or K⁺ concentration changes on the steady potential was observed. These results indicate that the ion permeability properties of the ovulated egg are similar to that of the ovarian oocyte in Ca-deficient medium, and suggests that the mechanism of ovulation may involve the removal of Ca⁺⁺ regulation of ion permeability of the egg cell membrane.     

Biomass production,nutrient cycling,and carbon fixation by Salicornia brachiata Roxb.: A promising halophyte for coastal saline soil rehabilitation

In order to increase our understanding of the interaction of soil-halophyte (Salicornia brachiata) relations and phytoremediation, we investigated the aboveground biomass, carbon fixation, and nutrient composition (N, P, K, Na, Ca, and Mg) of S. brachiata using six sampling sites with varying characteristics over one growing season in intertidal marshes. Simultaneously, soil characteristics and nutrient concentrations were also estimated. There was a significant variation in soil characteristics and nutrient contents spatially (except pH) as well as temporally. Nutrient contents in aboveground biomass of S. brachiata were also significantly differed spatially (except C and Cl) as well as temporally. Aboveground biomass of S. brachiata ranged from 2.51 to 6.07 t/ha at maturity and it was positively correlated with soil electrical conductivity and available Na, whereas negatively with soil pH. The K/Na ratio in plant was below one, showing tolerance to salinity. The aboveground C fixation values ranged from 0.77 to 1.93 C t/ha at all six sampling sites. This study provides new understandings into nutrient cycling—C fixation potential of highly salt-tolerant halophyte S. brachiata growing on intertidal soils of India. S. brachiata have a potential for amelioration of the salinity due to higher Na bioaccumulation factor.     

Regulation of cell volume and ion concentrations in aHalobacterium

Summary Changes in cell volume and ion content of aHalobacterium species are described in terms of the NaCl concentration (0.5–3.5m) and pH (4–8) of the suspending medium. Cell volume, per unit content of protein of bacteria in stationary phase cultures, rose as the [NaCl] of the growth medium was increased. Logarithmic-phase bacteria shrank as the pH fell from 7 to 5.5. These changes are characteristic of bacteria with a moderate or rapid rate of O₂ consumption. Starving (i.e. nonmetabolizing) bacteria, on the other hand, did not change in size within the above ranges of [NaCl] and pH. At lower values, however, such bacteria swelled and eventually lysed. Effects of low pH on cell ions are compared in metabolizing and starving bacteria, and it is shown that changes in the state of the cell K are correlated with movements of cell Na. It appears that the cell K is used to maintain cell [Na] below the NaCl concentration of the medium. The results are explained in terms of a model involving interactions between polyelectrolytes, salts and water in the concentrated cytoplasm of these halophilic organisms.     

Arginine vasopressin stimulation of cerebral microvascular endothelial cell Na-K-Cl cotransporter activity is V1 receptor and [Ca] dependent

Ischemia-induced brain edema formation is mediated by increased transport of Na and Cl across an intact blood-brain barrier (BBB). Our previous studies have provided evidence that a luminally located BBB Na-K-Cl cotransporter is stimulated during cerebral ischemia to increase transport of Na and Cl into the brain. The main focus of the present study was to evaluate the effects of arginine vasopressin (AVP), previously shown to be increased in the brain during ischemia and to promote edema formation, on activity of the BBB cotransporter. Cerebral microvascular endothelial cell (CMEC) monolayers were cultured in astroglial cell conditioned medium, and Na-K-Cl cotransporter activity was assessed as bumetanide-sensitive ⁸⁶Rb influx. In both human and bovine CMECs, as well as in freshly isolated microvessels, AVP stimulated cotransport activity. This stimulatory effect was mimicked by V₁ but not V₂ vasopressin agonists and was blocked by V₁ but not V₂ vasopressin antagonists. Consistent with a V₁ vasopressin receptor mechanism of action, AVP caused an increase in CMEC intracellular [Ca] that was blocked by a V₁ antagonist. Exposing the cells to [Ca]-free media and/or reducing intracellular [Ca] by BAPTA also blocked AVP stimulation of CMEC cotransporter activity, as did the phospholipase C inhibitor U-73122. Finally, we found that while stimulation of CMEC cotransporter activity by AVP occurred within minutes, it was also sustained for hours in the continued presence of AVP. These findings support the hypothesis that AVP, through a V₁ receptor- and [Ca]-dependent mechanism, stimulates the BBB Na-K-Cl cotransporter to participate in ischemia-induced edema formation. blood-brain barrier; stroke; cerebral ischemia; brain edema     

Effects of pH and bicarbonate on the nutrient status and growth of three Lupinus species

Aims

High pH, and high bicarbonate (HCO₃⁻) and calcium (Ca) availability characterise calcareous soils. High [Ca] only partially explains why some Lupinus species are calcifuge, so we explored high [HCO₃⁻] and high pH.

Methods

We grew six Lupinus genotypes in hydroponics with pH 5, 6.5 and 8^a (adjusted by KOH), and 8^b (adjusted by KHCO₃). Leaf symptoms and areas, root appearance and biomass were recorded; whole leaf and root nutrient concentrations, and leaf cellular phosphorus (P), Ca and potassium (K) concentrations were determined using elemental X-ray microanalysis.

Results

Chlorosis was observed in young leaves at high pH for L. angustifolius and L. cosentinii, and P deficiency at high pH for all genotypes. High pH decreased iron (Fe) and zinc (Zn) uptake in all genotypes. It also decreased lateral root growth, the uptake of P, K, Ca, and manganese (Mn) by all sensitive species; and translocation of P, Fe, Zn, Mn, and Ca to leaves in most sensitive species. However, leaf [Ca], leaf [K], [K] within each measured cell type, and translocation of K and Ca to leaves of L. pilosus and L. cosentinii at pH 8 were greater than at pH 5 and 6.5. Compared with pH 8^a, all L. angustifolius genotypes translocated more P, Fe, Zn, Mn and K from roots to leaves at pH 8^b. High pH did not affect the leaf cell types that accumulated P and Ca, but decreased the leaf cellular [P].

Conclusions

Lupinus angustifolius and L. cosentinii were sensitive to high [HCO₃⁻] and/or high pH; L. pilosus was relatively tolerant. High pH decreased lateral root growth and nutrient uptake, inhibiting growth of sensitive species. High [HCO₃⁻] diminished the negative effect of pH 8 on nutrient translocation to leaves in most L. angustifolius genotypes. This knowledge provides critical insights into the habits of Lupinus species to guide breeding of calcicole plants.