Osmoadaptation in representatives of haloalkaliphilic bacteria from soda lakes

The adaptation of microorganisms to life in brines allows two strategies: the accumulation of organic osmoregulators in the cell (as in many moderate halophiles, halomonads in particular) or the accumulation of inorganic ions at extremely high intracellular concentrations (as, for example, in haloanaerobes). To reveal the regularities of osmoregulation in haloalkaliphiles developing in soda lakes, Halomonas campisalis Z-7398-2 and Halomonas sp. AIR-2 were chosen as representatives of halomonads, and Natroniella acetigena, as a representative of haloanaerobes. It was established that, in alkaliphilic halomonads, the intracellular concentrations of inorganic ions are insufficient for counterbalancing the environmental osmotic pressure and balance is attained due to the accumulation of organic osmoregulators, such as ectoine and betaine. On the contrary, the alkaliphilic haloanaerobe N. acetigena employs K+, Na+, and Cl- ions for osmoregulation. High intracellular salt concentrations increasing with the content of Na+ in the medium were revealed in this organism. At a concentration of 1.91 M Na+ in the medium, N. acetigena accumulated 0.83 M K+, 0.91 M Na+, and 0.29 M Cl- in cells, and, with an increase in the Na+ content in the medium to 2.59 M, it accumulated 0.94 M K+, 1.98 M Na+, and 0.89 M Cl-, which counterbalanced the external osmotic pressure and provided for cell turgor. Thus, it was shown that alkaliphilic microorganisms use osmoregulation strategies similar to those of halophiles and these mechanisms are independent of the mechanism of pH homeostasis.     

Fluxes and compartmentation of K+, Na+ and Cl−, and action of auxins in suspension-cultured Petroselinum cells

Transport of ⁸⁶Rb⁺/K⁺, ²²Na⁺, ³⁶Cl^?, and [³H]indole acetic acid (IAA) has been studied on suspension-cultured cells of the parsley, Petroselinum crispum (Mill) Nym. By compartmental analysis two intracellular compartments of K⁺, Na⁺, and Cl^? have been identified and ascribed to the cytoplasm and vacuole; half-times of exchange were around 200 s and 5 h, respectively. According to the Ussing-Teorell flux equation, active transport is required for the influx into the cytoplasm at the plasmalemma (K⁺, Cl^?) and the tonoplast (K⁺, Na⁺, Cl^?). The plasmalemma permeability pattern, P_K:P_Na:P_Cl=1.00:0.24:0.38, features an increased chloride permeability compared with cells from higher plant tissues. IAA uptake showed an exponential timecourse, was half-maximal after 10 min, and a linear function of the IAA concentration from 10^?9 to 10^?5 M. IAA and 2,4-dichlorophenoxy acetic acid reduce the apparent influx of K⁺, Na⁺, Cl^? during the initial 30 min after addition and subsequently accelerate both in- and efflux of these ions. We discuss that auxins could affect the ion fluxes in a complex way, e.g. by protonophorous activity and by control of the hypothetical proton pump.     

Contributions of inorganic ions,soluble carbohydrates,and multiatomic alcohols to water homeostasis in <Emphasis Type="Italic">Artemisia lerchiana</Emphasis> and <Emphasis Type="Italic">A. pauciflora</Emphasis>

Two morphological forms of wormwood Artemisia lerchiana (f. erecta and f. nutans) and A. pauciflora Web. (morphological form erecta) were grown on sand culture at a range of NaCl concentrations in the nutrient medium and then assayed for Na⁺, K⁺, and Cl^? content in various organs. In addition, the content of mono-, di-, and trisaccharides and multiatomic alcohols (mannitol and glycerol); water content; and organ biomass were determined. All plants examined showed high NaCl tolerance, comparable to that of halophytes. They were able to maintain high tissue hydration under conditions of salinity-induced growth suppression. The intracellular osmotic pressure in wormwood organs was mainly determined by the presence of Na⁺, K⁺, and Cl^?, as well as by mono-, di-, and trisaccharides, mannitol, and glycerol. The high content of Na⁺ and Cl^? in wormwood organs was also observed in the absence of salinity, which implies the ability of these organs to absorb ions from diluted NaCl solutions and accumulate ions in cells of their tissues. With the increase in salinity, the content of Na⁺ and Cl^? in roots and leaves increased to even higher levels. It is concluded that the ability of wormwood plants to absorb and accumulate inorganic ions provides for sustainable high intracellular osmotic pressure and, accordingly, low water potential under drought and salinity conditions. Growing plants under high salinity lowered the content of monosaccharides in parallel with accumulation of the trisaccharide raffinose. It is supposed that soluble carbohydrates and multiatomic alcohols are not only significant for osmoregulation but also perform a protective function in wormwood plants. The lower osmotic pressure in root cells compared to that in leaf cells of all plants examined was mainly due to the gradient distribution of K⁺ and Cl^? between roots and leaves. The two Artemisia species and two morphological forms of A. lerchiana did not differ appreciably in the ways of water balance regulation. It is found that different morphologies of two A. lerchiana forms are unrelated to variations in intracellular osmotic and turgor pressures.     

Relations between intracellular ion activities and extracellular osmolarity inNecturus gallbladder epithelium

Summary The interactions between ion and water fluxes have an important bearing on osmoregulation and transepithelial water transport in epithelial cells. Some of these interactions were investigated using ion-selective microelectrodes in theNecturus gallbladder. The intracellular activities of K⁺ and Cl^– in epithelial cells change when the epithelium is adapted to transport in solutions of a low osmolarity. In order to achieve new steady states at low osmolarities, cells lost K⁺, Cl^– and some unidentified anions. Surprisingly, the apparent K⁺ concentration remained high: at an external osmolartity of 64 mOsm the intracellular K⁺ concentration averaged 95mm. This imbalance was sensitive to anoxia and ouabain. The effects of abrupt changes in the external osmolarities on the intracellular activities of Na⁺, K⁺ and Cl^– were also investigated. The gradients were effectuated by mannitol. The initial relative rates of change of the intracellular activities of Na⁺ and Cl^– were equal. The data were consistent with Na⁺ and Cl^– ions initially remaining inside the cell and a cell membraneL _p of 10^–3 cm sec^–1 osm^–1, which is close to the values determine by Spring and co-workers (K.R. Spring, A. Hope & B.-E. Persson, 1981.In: Water Transport Across Epithelia. Alfred Benzon Symposium 15. pp. 190–200. Munskgaard, Copenhagen). The initial rate of change of the intracellular activity of K⁺ was only 0.1–0.2 times the change observed in Na⁺ and Cl^– activities, and suggests that K⁺ ions leave the cell during the osmotically induced H₂O efflux and enter with an induced H₂O influx. The coupling is between 98 and 102 mmoles liter^–1. Various explanations for the anomalous behavior of intracellular K⁺ ions are considered. A discussion of the apparent coupling between K⁺ and H₂O, observed in nonsteady states, and its effects on the distribution of K⁺ and H₂O across the cell membrane in the steady states, is presented.     

Silicon nutrition alleviates physiological disorders imposed by salinity in hydroponically grown canola (Brassica napus L.) plants

The effects of Si nutrition on transpiration, leaf anatomy, accumulation of Na⁺, K⁺, Cl^?, P, Fe and B and some reactive oxygen species related parameters were investigated in canola plants under salinity. Plants were grown hydroponically in growth chamber under controlled conditions at 0 and 100?mM NaCl each supplied with or without 1.7?mM silicon (Si) as sodium silicate. Salinity imposed significant reduction in growth parameters of plants like fresh weights of roots and shoots and leaf area. It also led to accumulation of Na⁺ and Cl^? and a decrease in the concentration of K⁺, P, B and Fe. Reduction of transpiration, stomatal density and specific leaf area in leaves and an increase in leaf thickness were amongst other symptoms in salt-affected plants. Salinity led to higher concentration of hydrogen peroxide, increased lipid peroxidation and decrease of catalase and peroxidase activity, which suggests the induction of oxidative stress in plants. Silicon nutrition could prevent toxic ions (Na⁺ and Cl^?) accumulation while higher levels of essential minerals like K⁺, P and Fe were maintained in plants. Consequently, silicon nutrition decreased oxidative stress in plants, evidenced by increase in antioxidant enzyme activity, reduction in hydrogen peroxide and lipid peroxidation.     

Changes in K<Superscript>+</Superscript>, Na<Superscript>+</Superscript>, Cl<Superscript>−</Superscript> balance and K<Superscript>+</Superscript>, Cl<Superscript>−</Superscript> fluxes in U937 cells induced to apoptosis by staurosporine: On cell dehydration in apoptosis

The K⁺, Na⁺, and Cl⁻ balance and K⁺ (Rb⁺) and ³⁶Cl⁻ fluxes in U937 cells induced to apoptosis by 0.2 or 1 μM staurosporine were studied using flame emission and radioisotope techniques. It is found that two-thirds of the total decrease in the amount of intracellular osmolytes in apoptotic cells is accounted for by monovalent ions and one-third consists of other intracellular osmolytes. A decrease in the amount of monovalent ions results from a decrease in the amount of K⁺ and Cl⁻ and an increase in the Na⁺ content. The rate of ³⁶Cl⁻, Rb⁺ (K⁺), and ²²Na⁺ equilibration between cells and the medium was found to significantly exceed the rate of apoptotic change in the cellular ion content, which indicates that unidirectional influxes and effluxes during apoptosis may be considered as being in near balance. The drift of the ion flux balance in apoptosis caused by 0.2 μM staurosporine was found to be associated with the increased ouabain-resistant Rb⁺ (K⁺) channel influx and insignificantly altered the ouabain-sensitive pump influx. Severe apoptosis induced by 1 μM staurosporine is associated with reduced pump fluxes and slightly changed channel Rb⁺ (K⁺) fluxes. In apoptotic cells, the 1.4–1.8-fold decreased Cl⁻ level is accompanied by a 1.2–1.6-fold decreased flux.     

Vhc1, a novel transporter belonging to the family of electroneutral cation–Cl− cotransporters,participates in the regulation of cation content and morphology of Saccharomyces cerevisiae vacuoles

Cation–Cl^? cotransporters (CCCs) are integral membrane proteins which catalyze the coordinated symport of Cl^? with Na⁺ and/or K⁺ ions in plant and mammalian cells. Here we describe the first Saccharomyces cerevisiae CCC protein, encoded by the YBR235w open reading frame. Subcellular localization studies showed that this yeast CCC is targeted to the vacuolar membrane. Deletion of the YBR235w gene in a salt-sensitive strain (lacking the plasma-membrane cation exporters) resulted in an increased sensitivity to high KCl, altered vacuolar morphology control and decreased survival upon hyperosmotic shock. In addition, deletion of the YBR235w gene in a mutant strain deficient in K⁺ uptake produced a significant growth advantage over the parental strain under K⁺-limiting conditions, and a hypersensitivity to the exogenous K⁺/H⁺ exchanger nigericin. These results strongly suggest that we have identified a novel yeast vacuolar ion transporter mediating a K⁺–Cl^? cotransport and playing a role in vacuolar osmoregulation. Considering its identified function, we propose to refer to the yeast YBR235w gene as VHC1 (vacuolar protein homologous to CCC family 1).     

Malaria parasites tolerate a broad range of ionic environments and do not require host cation remodelling

Malaria parasites grow within erythrocytes, but are also free in host plasma between cycles of asexual replication. As a result, the parasite is exposed to fluctuating levels of Na⁺ and K⁺, ions assumed to serve important roles for the human pathogen, Plasmodium falciparum. We examined these assumptions and the parasite's ionic requirements by establishing continuous culture in novel sucrose‐based media. With sucrose as the primary osmoticant and K⁺ and Cl^? as the main extracellular ions, we obtained parasite growth and propagation at rates indistinguishable from those in physiological media. These conditions abolish long‐known increases in intracellular Na⁺ via parasite‐induced channels, excluding a requirement for erythrocyte cation remodelling. We also dissected Na⁺, K⁺ and Cl^? requirements and found that unexpectedly low concentrations of each ion meet the parasite's demands. Surprisingly, growth was not adversely affected by up to 148 mM K⁺, suggesting that low extracellular K⁺ is not an essential trigger for erythrocyte invasion. At the same time, merozoite egress and invasion required a threshold ionic strength, suggesting critical electrostatic interactions between macromolecules at these stages. These findings provide insights into transmembrane signalling in malaria and reveal fundamental differences between host and parasite ionic requirements.     

Na+ transport processes in isolated guinea pig nasal gland acinar cells

In the dispersed acinar cells of the submucosal nasal gland in the guinea pig, intracellular Na⁺ concentration ([Na⁺]i) was measured with a microfluorimetric imaging method and the cytosolic indicator dye, sodium-binding benzofuran isophthalate, under HCO₃^?-free conditions. In the unstimulated condition, the [Na⁺]i was averaged to 12.8 ± 5.2 mM. Addition of 100 μM ouabain or removal of external K⁺ caused an increase in [Na⁺]i. Replacement of external Cl^? with NO₃^? or addition of 0.5 mM furosemide reversibly decreased the [Na⁺]i. The recovery process from the reduced [Na⁺]i was inhibited by removal of either K⁺ or Cl^? in the bath solution. These findings indicate the presence of a continuous influx of Na⁺ coupled with K⁺ and Cl^? movement. Application of acetylcholine (ACh, 1 μM) caused an increase in [Na⁺]i by about 15–20 mM, which was completely inhibited by addition of 10 μM atropine. Increased cytosolic Na⁺ induced by ACh was extruded by the Na⁺-K⁺ pump. Removal of external Cl^? and addition of 50 μM dimethylamiloride inhibited ACh-induced increase in [Na⁺]i by about 66% and 19%, respectively. In both unstimulated and stimulated state, Na⁺-K⁺ pump, Na-K-Cl cotransport, and Na⁺-H⁺ exchange play a critical role in maintaining intracellular electrolyte environment and in controlling a continuous secretion of nasal fluids. © 1995 Wiley-Liss, Inc.     

Low MW carbohydrates and ions in rhodophyceae: Quantitative measurement of floridoside and digeneaside

The content of the heterosides floridoside and digeneaside and of the main ions Na⁺, K⁺, and Cl^? was estimated in 20 species of the Rhodophyceae. Methods for quantitative determination of the heterosides are described. The floridoside content is in the range of 1.5–8% on a dry weight basis (Catenella: up to 22%); the content of digeneaside, exclusively found in species of the Ceramiales, is lower, in the range of 1–2.2% on a dry weight basis. All species investigated have Cl^? as main anion, while there is a remarkable diversity in cation composition. Na⁺ was the major cation in 12 of the species investigated, the others having K⁺ as main cation.     

Different Ionic Specificities of ATP Synthesis in Extremely Alkaliphilic Sulfate-Reducing and Acetogenic Bacteria

Ionic specificity of oxidative phosphorylation was studied in Natroniella acetigenaand Desulfonatronum lacustre, which are new alkaliphilic anaerobes that were isolated from soda lakes and have a pH growth optimum of 9.5–9.7. The ability of their cells to synthesize ATP in response to the imposition of artificial pH⁺and pNa⁺gradients was studied. As distinct from other marine and freshwater sulfate reducers and extremely alkaliphilic anaerobes, D. lacustreuses a Na⁺-translocating ATPase for ATP synthesis. The alkaliphilic acetogen N. acetigena, which develops at a much higher Na⁺concentration in the medium, generated primary pH⁺for ATP synthesis. Thus, the high Na⁺concentrations and alkaline pH values typical of soda lakes do not predetermine the type of bioenergetics of their inhabitants.     

Dependence of the intracellular concentrations of univalent ions and hydrogenase activity on the salt composition and pH of the medium in the haloalkaliphilic sulfate-reducing bacterium <Emphasis Type="Italic">Desulfonatronum thiodismutans</Emphasis>

It has been shown that the intracellular concentrations of Na⁺, K⁺, and Cl^? ions in Desulfonatronum thiodismutans depend on the extracellular concentration of Na⁺ ions. An increase in the extracellular concentration of Na⁺ results in the accumulation of K⁺ ions in cells, which points to the possibility that these ions perform an osmoprotective function. When the concentration of the NaCl added to the medium was increased to 4%, the concentration gradient of Cl^? ions changed insignificantly. It was found that D. thiodismutans contains two forms of hydrogenase—periplasmic and cytoplasmic. Both enzymes are capable of functioning in solutions with high ionic force; however they exhibit different sensitivities to Na⁺, K⁺, and Li⁺ salts and pH. The enzymes were found to be resistant to high concentrations of Na⁺ and K⁺ chlorides and Na⁺ bicarbonate. The cytoplasmic hydrogenase differed significantly from the periplasmic one in having much higher salt tolerance and lower pH optimum. The activity of these enzymes depended on the nature of both the cationic and anionic components of the salts. For instance, the inhibitory effect of NaCl was less pronounced than that of LiCl, whereas Na⁺ and Li⁺ sulfates inhibited the activity of both hydrogenase types to an equal degree. The highest activity of these enzymes was observed at low Na⁺ concentrations, close to those typical of cells growing at optimal salt concentrations.     

Characterization of monovalent ion transport systems in an insect cell line (Manduca sexta embryonic cell line che)

The monovalent ion transport systems of an immortalized insect cell line (CHE) have been investigated. These cells are unusual in that unlike most vertebrate cells, their normal extracellular environment consists of high potassium and low sodium concentrations. CHE cells maintained high intracellular [K⁺] through both a furosemide-inhibitable and a vanadate-inhibitable transport system. Intracellular exchangeable [Na⁺] was slightly lower than the extracellular [Na⁺] and was maintained at this level through a vanadate-sensitive transport system. Na⁺ uptake was also inhibited by furosemide: however, the stoichiometry of furosemide-sensitive Na⁺ uptake when compared with furosemide-sensitive K⁺ uptake indicated that these cations are not cotransported. 4,4′-Diisothiocyano-2,2′-disulfonic acid stilbene (DIDS) inhibited Na⁺, K⁺, and Cl^? uptake. Vanadate and furosemide decreased cytoplasmimic pH, while cytoplasmic pH increased in the presence of DIDS. A model is presented explaining how Na⁺, K⁺, Cl^?, H⁺ and HCO₃ ^? fluxes are regulated in these cells.     

The relationship between sodium,potassium, and chloride in amphibian muscle

The Na,⁺ Cl^-, and K⁺ content of toad plasma and the sartorius muscle has been determined. Although the Na⁺ and Cl^- level of the muscles in the living animal varied greatly (0 to 38.0 m.eq. per kg., and 0 to 31.8 m.eq. per kg. respectively) the K⁺ level was subject to a smaller variation (76.5 to 136 m.eq. per kg.). There was a direct relationship between Na⁺ and Cl^-, which was independent of the K⁺ level. There is a closely related gain of Na⁺ and Cl^- when muscle is soaked in normal Ringer. These gains are not related to the K⁺ loss, frequently found on soaking. The relationship between the three ions was studied in a large series of 124 muscles in normal Ringer. As found in vivo, there was a correlation between Na⁺ and Cl.^- This correlation was independent of K⁺ content, except when this was abnormally low. Alteration of the external NaCl level produced concomitant changes in the internal levels of these ions. Alteration of the external KCl level produced an increase in internal Cl^- similar to that found with high NaCl solutions, but the amount of K⁺ entering the cell was approximately one-third of the external increase. Removal of K⁺ from the external solution did not result in a loss of K⁺ from the cell, although there was an adequate amount of Cl^- present to accompany it. The results cannot be reconciled with either a Donnan concept for the accumulation of K⁺, or a linked carrier system. A theory is proposed to account for the ionic differentiation within the cell. The K⁺ is assumed to be adsorbed onto an ordered intracellular phase. The normal metabolic functioning of the cell is necessary to maintain the specificity of the adsorption sites. There is another intracellular phase, which lacks the structural specificity for K⁺, and which contains Na⁺, Cl^-, and K⁺ in equilibrium with the external solution. The dimensions of the free intracellular phase will vary from cell to cell, but it will be smaller in the intact animal, and will increase on soaking in normal Ringer, until it is approximately one-third of the total cellular volume. The increase in this phase may be ascribed to a decrease in the energy available to maintain the ordered phase.     

Electrically silent cotransport of Na+, K+ and Cl− in ehrlich cells

A cotransport system for Na⁺, K⁺ and Cl^? in Ehrlich cells is described. It is insensitive towards ouabain but specifically inhibited by furosemide and other ‘high ceiling’ diuretics at concentrations which do not affect other pathways of the ions concerned. As the furosemide-sensitive fluxes of these ions are not affected by changes in membrane potential, and as their complete inhibition by furosemide does not appreciably alter the membrane potential, they appear to be electrically silent. Application of the pulse-response methods in terms of irreversible thermodynamics reveals tight coupling between the furosemide-sensitive flows of Na⁺, K⁺ and Cl^? ($\text{q}$ close to unity for all three combinations) at a stoichiometry of 1 : 1 : 2. The site for each of the ions appears to be rather specific: K⁺ can be replaced by Rb⁺ but not by other cations tested whereas Cl^? can be poorly replaced by Br^? but not by NO₃^?, in contradistinction to the Cl^?-OH^? exchange system. The cotransport system appears to function in cell volume regulation as it tends to make the cell swell, thus counteracting the shrinking effect of the ouabain-sensitive (Na⁺, K⁺) pump.The experiments presented could not clarify whether the cotransport process is a primary or secondary active one; while incongruence between transport and conjugated driving force seems to indicate primary active transport, it is very unlikely that hydrolysis of ATP supplies energy for the transport process, since there is no stimulation of ATP turnover observable under operation of the cotransport system.     

Intracellular compartmentation of Na+, K+ and Cl− in the Ehrlich ascites tumor cell: Correlation with the membrane potential

Summary The intracellular distribution of Na⁺, K⁺, Cl^– and water has been studied in the Ehrlich ascites tumor cell. Comparison of the ion and water contents of whole cells with those of cells exposed to La³⁺ and mechanical stress indicated that La³⁺ treatment results in selective damage to the cell membrane and permits evaluation of cytoplasmic and nuclear ion concentrations. The results show that Na⁺ is sequestered within the nucleus, while K⁺ and Cl^– are more highly concentrated in the cell cytoplasm. Reduction of the [Na⁺] of the incubation medium by replacement with K⁺ results in reduced cytoplasmic [Na⁺], increased [Cl^–] and no change in [K⁺]. Nuclear concentrations of these ions are virtually insensitive to the cation composition of the medium. Concomitant measurements of the membrane potential were made. The potential in control cells was –13.7 mV. Reduction of [Na⁺] in the medium caused significant depolarization. The measured potential is describable by the Cl^– equilibrium potential and can be accounted for in terms of cation distributions and permeabilities. The energetic implications of the intracellular compartmentation of ions are discussed.     

Vasoconstriction triggered by hydrogen sulfide: Evidence for Na+,K+,2Cl-cotransport and L-type Ca2+ channel-mediated pathway

ObjectivesThis study examined the dose-dependent actions of hydrogen sulfide donor sodium hydrosulphide (NaHS) on isometric contractions and ion transport in rat aorta smooth muscle cells (SMC).MethodsIsometric contraction was measured in ring aortas segments from male Wistar rats. Activity of Na⁺/K⁺-pump and Na⁺,K⁺,2Cl^-cotransport was measured in cultured endothelial and smooth muscle cells from the rat aorta as ouabain-sensitive and ouabain-resistant, bumetanide-sensitive components of the ⁸⁶Rb influx, respectively.ResultsNaHS exhibited the bimodal action on contractions triggered by modest depolarization ([K⁺]_o=30 mM). At 10^?4 M, NaHS augmented contractions of intact and endothelium-denuded strips by ~ 15% and 25%, respectively, whereas at concentration of 10^?3 M it decreased contractile responses by more than two-fold. Contractions evoked by 10^?4 M NaHS were completely abolished by bumetanide, a potent inhibitor of Na⁺,K⁺,2Cl^-cotransport, whereas the inhibition seen at 10^?3 M NaHS was suppressed in the presence of K⁺ channel blocker TEA. In cultured SMC, 5×10^?5 M NaHS increased Na⁺,K⁺,2Cl^- - cotransport without any effect on the activity of this carrier in endothelial cells. In depolarized SMC, ⁴⁵Ca influx was enhanced in the presence of 10^?4 M NaHS and suppressed under elevation of [NaHS] up to 10^?3 M. ⁴⁵Ca influx triggered by 10^?4 M NaHS was abolished by bumetanide and L-type Ca²⁺ channel blocker nicardipine.ConclusionsOur results strongly suggest that contractions of rat aortic rings triggered by low doses of NaHS are mediated by activation of Na⁺,K⁺,2Cl^-cotransport and Ca²⁺ influx via L-type channels.     

Effects of low salinity media on growth, condition, and gill ion transporter expression in juvenile Gulf killifish, Fundulus grandis

The Gulf killifish, Fundulus grandis, is a euryhaline teleost which has important ecological roles in the brackish-water marshes of its native range as well as commercial value as live bait for saltwater anglers. Effects of osmoregulation on growth, survival, and body condition at 0.5, 5.0, 8.0 and 12.0‰ salinity were studied in F. grandis juveniles during a 12-week trial. Relative expression of genes encoding the ion transport proteins Na⁺/K⁺-ATPase (NKA), Na⁺/K⁺/2Cl⁻ cotransporter(NKCC1), and cystic fibrosis transmembrane conductance regulator (CFTR) Cl⁻ channel was analyzed. At 0.5‰, F. grandis showed depressed growth, body condition, and survival relative to higher salinities. NKA relative expression was elevated at 7 days post-transfer but decreased at later time points in fish held at 0.5‰ while other salinities produced no such increase. NKCC1, the isoform associated with expulsion of ions in saltwater, was downregulated from week 1 to week 3 at 0.5‰ while CFTR relative expression produced no significant results across time or salinity. Our results suggest that Gulf killifish have physiological difficulties with osmoregulation at a salinity of 0.5‰ and that this leads to reduced growth performance and survival while salinities in the 5.0-12.0‰ are adequate for normal function.     

Stimulated fluid secretion is sodium dependent in the Malpighian tubules of Locusta migratoria

The ionic dependencies of stimulated and unstimulated Locusta tubules have been studied. K⁺, Na⁺, Cl^? are essential to both basal and stimulated secretion. K⁺ is secreted against a concentration gradient in unstimulated tubules. In response to diuretic hormone or cAMP application, there is a dramatic influx of K⁺ into the lumen. A high level of Na⁺ and Cl^? in the bathing medium is required to allow maximal fluid secretion. The tubules show an apparent impermeability to Na⁺; its concentration in the secreted fluid is always much less than in the bathing medium. If Na⁺ is omitted from the medium and excess K⁺ added (80 mM K), then although basal secretion occurs (2.5 nl/min), the tubules fail to respond to stimulation. Clearly Na⁺ has an important indirect role to play in stimulated fluid secretion.     

Peroxidase activities of two rice cultivars differing in salinity tolerance as affected by proline and NaCl

Proline content, ion accumulation, cell wall and soluble peroxidase activities were determined in control and salt-treated calli (150 nM NaCl) and whole plants (30 mM NaCl) of two rice cultivars (salt sensitive cv. IKP and salt tolerant cv. Aiwu). Under salinity, the highest accumulation of Na⁺, Cl^? and proline occurred in calli, roots and younger leaves of cv. IKP, coupled with the highest decrease in K⁺ content; accumulations of Na⁺ and Cl^? were restricted to older leaves in cv. Aiwu. Relative growth rates of calli and roots or shoots from both cultivars were not linked to peroxidase activities. High concentrations (1 M) of exogenously applied glycerol did not inhibitin vitro activities of soluble peroxidase extracted from control and salt-treated calli or plants. Conversely, 35–55% (in cv. IKP) or 60–80% (in cv. Aiwu) of soluble peroxidase activities were found in presence of isosmotic proline concentration. There were no differences between proline and glycerol effects onin vitro cell wall peroxidase activities.