Response of sugarcane to different types of salt stress

Summary Due to climatic conditions and prevailing water regime the yield and sucrose recovery in sugarcane are high in South Western India. However, excessive irrigation, poor drainage and luxuriant use of fertilizers have resulted in conversion of large fertile areas into saline lands. The salinity is due to the excess of Na⁺, Ca⁺⁺, Mg⁺⁺, SO₄ ^– and Cl^– ions. Individual salts of NaCl, Na₂SO₄, MgCl₂ and MgSO₄ were employed in culture experiments to study salt stress effect on sugarcane variety Co 740. It was observed that sulphate salinity was more toxic to sugarcane than the chloride one. Sulphate salts caused more inhibition of growth, chlorophyll synthesis, PEPCase activity, decreased the uptake of K⁺ and Ca⁺⁺ ions but stimulated nitrate reductase. The stress did not result in proline accumulation in the sugarcane cultivar Co 740. The degree of toxicity of different ions in decreasing order in sugarcane cultivar Co 740 is SO₄ ^–>Na⁺>Cl^–>Mg⁺⁺.     

Intracellular and luminal ion concentrations in sea turtle salt glands determined by x-ray microanalysis

Summary The lachrymal salt glands of hatchlings of the green sea turtle (Chelonia mydas) secrete a hyperosmotic (up to 2000 mosmol·kg^–1) NaCl solution. X-ray microanalysis of frozen-hydrated glands showed that during secretion intracellular Na⁺ concentration in the principal cells increased from 13 to 34 mmol·l^–1 of cell water, whilst Cl^– and K⁺ concentrations remained unchanged at 81 mmol·l^–1 and 160–174 mmol·l^–1, respectively. The high Cl^– concentration and the change in Na⁺ concentration are consistent with the prevailing paradigm for secretion by the structurally and functionally similar elasmobranch rectal gland. Concentrations of Na⁺, Cl^– and K⁺ in the lumina of secretory tubules of secreting (Na⁺ 122, Cl^– 167, K⁺ 38 mmol·l^–1) and non-secreting (Na⁺ 114, Cl^–1 174, K⁺ 44 mmol·l^–1) glands were similar and the fluid was calculated to be approximately isosmotic with blood. In the central canals Na⁺ and Cl^– concentrations were similar but K⁺ concentration was lower (11–15 mmol·l^–1). It is concluded that either a high transepithelial NaCl gradient in secretory tubules and central canals is very rapidly dissipated during the short time between gland excision and freezing, or that ductal modification of an initial isosmotic secretion occurs.     

On the interrelations of the Na+-and Cl?-influxes in the pulmonate freshwater snailLymnaea stagnalis

Summary In the freshwater snailLymnaea stagnalis the influxes of Na⁺ and Cl^– were studied at different external concentrations of these ions. The characteristies of the Na⁺- and Cl^–-influxes are similar with respect to saturation kinetics,K _m (0.1 mM) and activation by low-salt adaptation. In short-term experiments the Na⁺- and Cl^–-influxes are independent. Because of the counter-ions (H⁺ and HCO ₃ ^– ) involved, this indicates a potential acid-base regulatory capacity. Low-salt adaptation, due to either Na⁺-or Cl^–-depletion, activates both the Na⁺- and the Cl^–-influx. It is suggested that under both conditions the number of active integumental pumps, involved in Na⁺- as well as in Cl^–-uptake, is increased.     

Active NaCl absorption across split lamellae of posterior gills of Chinese crabs (Eriocheir sinensis) adapted to different salinities

Split lamellae of posterior gills of Eriocheir sinensis adapted to fresh water, brackish waters (9 or 18‰) or seawater (36‰) were mounted in Ussing chambers, and transepithelial short-circuit currents and conductances were measured with salines, containing approximately in vivo-like NaCl concentrations. Active sodium and chloride absorption (I_Na and I_Cl), the transcellular conductances and the leak conductance were identified with external amiloride and/or DIDS. Split gill lamellae of crabs adapted to fresh water displayed similar magnitudes of I_Na and I_Cl with 10 mmol l⁻¹ NaCl in the external medium (internally haemolymph-like NaCl saline). Augmenting external NaCl (50 mmol l⁻¹) resulted in an increase of I_Cl, whereas I_Na decreased. Split gill lamellae of crabs adapted to brackish waters (external NaCl of 125 and 225 mmol l⁻¹, respectively) showed lower currents than preparations of freshwater crabs (50 mmol l⁻¹ external NaCl). With split gill lamellae of seawater crabs no currents were detected (450 mmol l⁻¹ NaCl on both sides). The transcellular conductances showed similar changes as the currents. The leak conductance of split gill lamellae of crabs adapted to fresh or brackish waters was low (0.3–0.8 mS cm⁻²), whereas it was much higher (7 mS cm⁻²) with preparations of seawater crabs.     

Cl−, Na+, and H+ fluxes during the acidification of rabbit reticulocyte endocytic vesicles

The ionic fluxes associated with the ATP-dependent acidification of endocytic vesicles were studied in a preparation isolated from rabbit reticulocytes enriched for transferrin-transferrin receptor complexes. No vesicle acidification was observed in the absence of intra- and extravesicular ions (sucrose_in/sucrose_out), while maximal acidification was observed with NaCl_in/KCl_out·K _in ⁺ was a poor substitute for Na _in ⁺ , and Cl _out ^– could be replaced by other anions with the following efficacy of acidification: Cl^–>Br^–>I^–>PO ₄ ^3– >gluconate>SO ₄ ^2– . Flux studies using³⁶Cl^– and²²Na⁺ showed that the vesicles had a permeability for Cl^– and Na⁺, and that ATP-dependent H⁺ pumping was accompanied by a net influx of Cl^– and a net efflux of Na⁺ provided that there was a Na⁺ concentration gradient. After 3 mins, the time necessary to maximal acidification, the electrical charge generated by the entrance of H⁺ was countered to about 45% by the Cl^– influx and to about 42% by the Na⁺ efflux. These studies demonstrated that both Cl^– and Na⁺ fluxes are necessary for optimal endocytic vesicle acidification.     

Relationship between coupled Na+−K+−Cl− transport and water absorption across the seawater eel intestine

Summary Simultaneous measurements of net ion and water fluxes were made in the stripped intestine of the seawater eel, and the relationship between Na⁺, K⁺, Cl^– and water transport were examined in the presence of mucosal KCl and serosal NaCl Ringer (standard condition). When Cl^– was removed from both sides of the intestine, net K⁺ flux from mucosa to serosa was reduced, accompanied by complete blockage of water absorption. Since it has been shown that net Cl^– and water fluxes depend on K⁺ transport under the standard condition (Ando 1983), the interdependence of K⁺ and Cl^– transport suggests the existence of a coupled KCl transport system, while the parallelism between the net Cl^– and water fluxes suggests that water absorption is linked to the coupled KCl transport. The coupled KCl and water transport were inhibited by treatment with ouabain or with Na⁺-free Ringer solutions, suggesting the existence of a Na⁺-dependent KCl transport system and linkage of water absorption to the coupled Na⁺–K⁺–Cl^– transport. Since ouabain blocked the active Na⁺–K⁺–Cl^– transport almost completely, the permeability coefficients for K⁺ and Na⁺ through the paracellular shunt pathway were estimated as P_K=0.076 and P_Na=0.058 cm/h, and P_Cl was calculated as 0.005 cm/h. Although Na⁺-independent K⁺ and Cl^tt- fluxes were observed again in the present study, these fluxes were not inhibited by CN^–, ouabain or diuretics, and evoked even after blocking the Na⁺–K⁺–Cl^– transport completely with ouabain. These results indicate that the Na⁺-independent K⁺ and Cl^– fluxes are distinct from the active Na⁺–K⁺–Cl^– transport and are not themselves active.     

Na+-coupled Cl− transport in the gastric mucosa of the guinea pig

The Cl^–/HCO ₃ ^– exchange mechanism usually postulated to occur in gastric mucosa cannot account for the Na⁺-dependent electrogenic serosal to mucosal Cl^– transport often observed. It was recently suggested that an additional Cl^– transport mechanism driven by the Na⁺ electrochemical potential gradient may be present on the serosal side of the tissue. To verify this, we have studied Cl^– transport in guinea pig gastric mucosa. Inhibiting the (Na⁺, K⁺) ATPase either by serosal addition of ouabain or by establishing K⁺-free mucosal and serosal conditions abolished net Cl^– transport. Depolarizing the cell membrane potential with triphenylmethylphosphonium (a lipid-soluble cation), and hence reducing both the Na⁺ and Cl^– electrochemical potential gradients, resulted in inhibition of net Cl^– flux. Reduction of short-circuit current on replacing Na⁺ by choline in the serosal bathing solution was shown to be due to inhibition of Cl^– transport. Serosal addition of diisothiocyanodisulfonic acid stilbene (an inhibitor of anion transport systems) abolished net Cl^– flux but not net Na⁺ flux. These results are compatible with the proposed model of a Cl^–/Na⁺ cotransport mechanism governing serosal Cl^– entry into the secreting cells. We suggest that the same mechanism may well facilitate both coupled Cl^–/Na⁺ entry and coupled HCO ₃ ^– /Na⁺ exit on the serosal side of the tissue.     

Stimulation by HCO 3 − of Na+ transport in rabbit gallbladder

Summary Bicarbonate presence in the bathing media doubles Na⁺ and fluid transepithelial transport and in parallel significantly increases Na⁺ and Cl^– intracellular concentrations and contents, decreases K⁺ cell concentration without changing its amount, and causes a large cell swelling. Na⁺ and Cl^– lumen-to-cell influxes are significantly enhanced, Na⁺ more so than Cl^–. The stimulation does not raise any immediate change in luminal membrane potential and cannot be due to a HCO ₃ ^– -ATPase in the brush border. The stimulation goes together with a large increase in a Na⁺-dependent H⁺ secretion into the lumen. All of these data suggests that HCO ₃ ^– both activates Na⁺–Cl^– cotransport and H⁺–Na⁺ countertransport at the luminal barrier.Thiocyanate inhibits Na⁺ and fluid transepithelial transport without affecting H⁺ secretion and HCO ₃ ^– -dependent Na⁺ influx. It reduces Na⁺ and Cl^– concentrations and contents, increases the same parameters for K⁺, causes a cell shrinking, and abolishes the lumen-to-cell Cl^– influx. It enters the cell and is accumulated in the cytoplasm with a process which is Na⁺-dependent and HCO ₃ ^– -activated. Thus, SCN^– is likely to compete for the Cl^– site on the cotransport carrier and to be slowly transferred by the cotransport system itself.     

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.     

Kinetic mechanism of Na+, K+, Cl−-cotransport as studied by Rb+ influx into HeLa cells: Effects of extracellular monovalent ions

Summary Ouabain-insensitive, furosemide-sensitive Rb⁺ influx (J _Rb) into HeLa cells was examined as functions of the extracellular Rb⁺, Na⁺ and Cl^– concentrations. Rate equations and kinetic parameters, including the apparent maximumJ _Rb, the apparent values ofK _m for the three ions and the apparentK _i for K⁺, were derived. Results suggested that one unit molecule of this transport system has one Na⁺, one K⁺ and two Cl^– sites with different affinities, one of the Cl^– sites related with binding of Na⁺, and the other with binding of K⁺(Rb⁺). A 11 stoichiometry was demonstrated between ouabain-insensitive, furosemidesensitive influxes of²²Na⁺ and Rb⁺, and a 12 stoichiometry between those of Rb⁺ and³⁶Cl^–. The influx of either one of these ions was inhibited in the absence of any one of the other two ions. Monovalent anions such as nitrate, acetate, thiocyanate and lactate as substitutes for Cl^– inhibited ouabain-insensitive Rb⁺ influx, whereas sulfamate and probably also gluconate did not inhibitJ _Rb. From the present results, a general model and a specialized cotransport model were proposed: 1) In HeLa cells, one Na⁺ and one Cl^– bind concurrently to their sites and then one K⁺ (Rb⁺) and another Cl^– bind concurrently. 2) After completion of ion bindings Na⁺, K⁺(Rb^–) and Cl^– in a ratio of 112 show synchronous transmembrane movements.     

Na+ and Cl− conductances are controlled by cytosolic Cl− concentration in the intralobular duct cells of mouse mandibular glands

Our previously published whole-cell patch-clamp studies on the cells of the intralobular (granular) ducts of the mandibular glands of male mice revealed the presence of an amiloride-sensitive Na⁺ conductance in the plasma membrane. In this study we demonstrate the presence also of a Cl^– conductance and we show that the sizes of both conductances vary with the Cl^– concentration of the fluid bathing the cytosolic surface of the plasma membrane. As the cytosolic Cl^– concentration rises from 5 to 150 mmol/liter, the size of the inward Na⁺ current declines, the decline being half-maximal when the Cl^– concentration is approximately 50 mmol/liter. In contrast, as cytosolic Cl^– concentration increases, the inward Cl^– current remains at a constant low level until the Cl^– concentration exceeds 80 mmol/liter, when it begins to increase. Studies in which Cl^– in the pipette solution was replaced by other anions indicate that the Na⁺ current is suppressed by intracellular Br^-, Cl^– and NO ₃ ^- but not by intracellular I^-, glutamate or gluconate. Our studies also show that the Cl^– conductance allows passage of Cl^– and Br^- equally well, I-less well, and NO ₃ ^- , glutamate and gluconate poorly, if at all. The findings with NO ₃ ^- are of particular interest because they show that suppression of the Na⁺ current by a high intracellular concentration of a particular anion does not depend on actual passage of that anion through the Cl^– conductance. In mouse granular duct cells there is, thus, a reciprocal regulation of Na⁺ and Cl^– conductances by the cytosolic Cl^– concentration. Since the cytosolic Cl^– concentration is closely correlated with cell volume in many epithelia, this reciprocal regulation of Na⁺ and Cl^– conductances may provide a mechanism by which ductal Na⁺ and Cl transport rates are adjusted so as to maintain a stable cell volume.This project was supported by the National Health and Medical Research Council of Australia. We thank Professor P. Barry (University of New South Wales) for assistance with the junction potential measurements.     

Changes in haemolymph ion concentrations of Astacus astacus L. and Pacifastacus leniusculus (Dana) after exposure to low pH and aluminium

During exposure to soft water, acidified to pH 4.0, the haemolymph concentrations of Na⁺, K⁺, and Cl^– decreased whereas the Ca²⁺ concentration fluctuated in Astacus astacus. The haemocyte content of K⁺ decreased from 9% to 2% of the total haemolymph K⁺ content after exposure to pH 3.7 for 3 days. Within 14 days, 250 µg Al³⁺ l^–1, as Al₂(SO₄)₃ at pH 5.0, reduced the haemolymph Na⁺ content in Astacus astacus and Pacifastacus leniusculus, however, the effects were less pronounced than earlier reported for fish. Disturbed ion regulation, mainly depending on low pH, is thought to contribute to the absence of these species in acid waters.     

Naphthenic acids affect plant water conductance but do not alter shoot Na+ and Cl− concentrations in jack pine (Pinus banksiana) seedlings

Solution culture-grown, six-month old jack pine (Pinus banksiana Lamb.) seedlings were treated with naphthenic acids (NAs) (150 mg l^–1) and sodium chloride (45 mM NaCl) which were applied together or separately to roots for four weeks. NAs aggravated the effects of NaCl in inhibiting stomatal conductance (g _s) and root hydraulic conductance (K_r). Naphthenic acids did not affect needle and root electrolyte leakage in the absence of NaCl. However, in plants treated with NaCl, NAs further increased electrolyte leakage from needles and NaCl induced electrolyte leakage from needles, but not from roots. Both NaCl and NAs treatments resulted in a reduction in root respiration. The measured Na⁺ and Cl^– concentrations in the shoots for combined NaCl + NAs treatments were lower than in NaCl-only treatments. These decreases were correlated with a reduction in water conductance. The accumulation of Na⁺ and Cl^– in shoots was accompanied by an increased in needle electrolyte leakage. However, greater concentrations of Cl^– compared with Na⁺ were present in shoots and in the xylem sap suggesting that roots had relatively lower capacity for Cl^– storage compared with Na⁺.     

Passive sodium movements across the opercular epithelium: The paracellular shunt pathway and ionic conductance

Summary The unidirectional Na⁺, Cl^–, and urea fluxes across isolated opercular epithelia from seawater-adaptedFundulus heteroclitus were measured under different experimental conditions. The mean Na⁺, Cl^–, and urea permeabilities were 9.30×10^–6 cm·sec^–1, 1.24×10^–6 cm·sec^–1, and 5.05×10^–7 cm·sec^–1, respectively. The responses of the unidirectional Na⁺ fluxes and the Cl^– influx (mucosa to serosa) to voltage clamping were characteristic of passively moving ions traversing only one rate-limiting barrier. The Na⁺ conductance varied linearly with, and comprised a mean 54% of, the total tissue ionic conductance. The Cl^– influx and the urea fluxes were independent of the tissue conductance. Triaminopyrimidine (TAP) reduced the Na⁺ fluxes and tissue conductance over 70%, while having no effect on the Cl^– influx or urea fluxes. Mucosal Na⁺ substitution reduced the Na⁺ permeability 60% and the tissue conductance 76%, but had no effect on the Cl^– influx or the urea fluxes. Both the Na⁺ and Cl^– influxes were unaffected by respective serosal substitutions, indicating the lack of any Na⁺/Na⁺ and Cl^–/Cl^– exchange diffusion.The results suggest that the unidirectional Na⁺ fluxes are simple passive fluxes proceeding extracellularly (i.e., movement through a cation-selective paracellular shunt). This pathway is dependent on mucosal (external) Na⁺, independent of serosal (internal) Na⁺, and may be distinct from the transepithelial Cl^– and urea pathways.     

The nature of the neutral Na+−Cl− coupled entry at the apical membrane of rabbit gallbladder epithelium: III. Analysis of transports on membrane vesicles

Summary In rabbit gallbladder epithelium, a Na⁺/H⁺, Cl^–/HCO ₃ ^– double exchange and a Na⁺–Cl^– symport are both present, but experiments on intact tissue cannot resolve whether the two transport systems operate simultaneously. Thus, isolated apical plasma membrane vesicles were prepared. After preloading with Na⁺, injection into a sodium-free medium caused a stable intravesicular acidification (monitored with the acridine orange fluorescence quenching method) that was reversed by Na⁺ addition to the external solution. Although to a lesser extent, acidification took place also in experiments with an electric potential difference (PD) equal to 0. If a preset pH difference (pH) was imposed ([H⁺]_in>[H⁺]_out, PD=0), the addition of Na-gluconate to the external solution caused pH dissipation at a rate that followed saturation kinetics. Amiloride (10^–4 m) reduced the pH dissipation rate. Taken together, these data indicate the presence of Na⁺ and H⁺ conductances in addition to an amiloride-sensitive, electroneutral Na⁺/H⁺ exchange.An inwardly directed [Cl^–] gradient (PD=0) did not induce intravesicular acidification. Therefore, in this preparation, there was no evidence for the presence of a Cl^–/OH^– exchange.When both [Na⁺] and [Cl^–] gradients (outwardly directed, PD=0) were present, fluorescence quenching reached a maximum 20–30 sec after vesicle injection and then quickly decreased. The decrease was not observed in the presence of a [Na⁺] gradient alone or the same [Na⁺] gradient with Cl^– at equal concentrations at both sides. Similarly, the decrease was abolished in the presence of both Na⁺ and Cl^– concentration gradients and hydrochlorothiazide (5×10^–4 m). The decrease was not influenced by an inhibitor of Cl^–/OH^– exchange (10^–4 m furosemide) or of Na⁺–K⁺–2Cl^– symport (10^–5 m bumetanide).We conclude that a Na⁺/H⁺ exchange and a Na⁺–Cl^– symport are present and act simultaneously. This suggests that in intact tissue the Na⁺–Cl^– symport is also likely to work in parallel with the Na⁺/H⁺ exchange and does not represent an induced homeostatic reaction of the epithelium when Na⁺/H⁺ exchange is inhibited.     

Studies on chloride permeability of the skin ofLeptodactylus ocellatus: II. Na+ and Cl− effect of inward movements of Cl−

Summary At low concentration (1mm) of Cl^– in the outer solution, the influx of chloride through the isolated skin (J ₁₃ ^Cl ) of the South American frogLeptodactylus ocellatus (L.) seems to be carried by two mechanisms: (i) a passive one that exhibits the characteristics of an exchange diffusion process, and (ii) an active penetration. Studies of the influx and efflux of chloride (J ₁₃ ^Cl andJ ₃₁ ^Cl ) indicate, that the presence of a high (107mm) concentration of Cl^– in the outer solution activates the translocation of this ion through the cells. Studies of the unidirectional flux of Cl^– across the outer barrier (J ₁₂ ^Cl ) indicate that Na⁺ out stimulates the penetration of Cl^– at this level. Cl^– out, in turn, stimulates, theJ ₁₂ ^Na , but this effect is only detected at low concentrations of Na⁺ out.     

Electrogenic Cl− absorption byAmphiuma small intestine: Dependence on serosal Na+ from tracer and Cl− microelectrode studies

Summary The Na⁺ requirement for active, electrogenic Cl^– absorption byAmphiuma small intestine was studied by tracer techniques and double-barreled Cl^–-sensitive microelectrodes. Addition of Cl^– to a Cl^–-free medium bathingin vitro intestinal segments produced a saturable (K _m =5.4mm) increase in shortcircuit current (I _sc) which was inhibitable by 1mm SITS. The selectivity sequence for the anion-evoked current was Cl^–=Br^–>SCN^–>NO ₃ ^– >F^–=I^–. Current evoked by Cl^– reached a maximum with increasing medium Na concentration (K _m =12.4mm). Addition of Na⁺, as Na gluconate (10mm), to mucosal and serosal Na⁺-free media stimulated the Cl^– current and simultaneously increased the absorptive Cl^– flux (J _ms ^Cl ) and net flux (J _net ^Cl ) without changing the secretory Cl^– flux (J _sm ^Cl ). Addition of Na⁺ only to the serosal fluid stimulatedJ _ms ^Cl much more than Na⁺ addition only to the mucosal fluid in paired tissues. Serosal DIDS (1mm) blocked the stimulation. Serosal 10mm Tris gluconate or choline gluconate failed to stimulateJ _ms ^Cl . Intracellular Cl^– activity (a _Cl ⁱ ) in villus epithelial cells was above electrochemical equilibrium indicating active Cl^– uptake. Ouabain (1mm) eliminated Cl^– accumulation and reduced the mucosal membrane potential _m over 2 to 3 hr. In contrast, SITS had no effect on Cl^– accumulation and hyperpolarized the mucosal membrane. Replacement of serosal Na⁺ with choline eliminated Cl^– accumulation while replacement of mucosal Na⁺ had no effect. In conclusion by two independent methods active electrogenic Cl^– absorption depends on serosal rather than mucosal Na⁺. It is concluded that Cl^– enters the cell via a primary (rheogenic) transport mechanism. At the serosal membrane the Na⁺ gradient most likely energizes H⁺ export and regulates mucosal Cl^– accumulation perhaps by influencing cell pH or HCO ₃ ^– concentration.     

Prostaglandin E2 enhances the sodium conductance of exocrine glands in isolated frog skin (Rana esculenta)

Summary Prostaglandins are known to stimulate the active transepithelial Na⁺ uptake and the active secretion of Cl^– from the glands of isolated frog skin. In the present work the effect of prostaglandin E₂ (PGE₂) on the glandular Na⁺ conductance was examined. In order to avoid interference from the Na⁺ uptake and the glandular Cl^– secretion the experiments were carried out on skins where the Cl^– secretion was inhibited (the skins were bathed in Cl^– Ringer's solution in the presence of furosemide, or in NO ₃ ^– Ringer's solution), and the active Na⁺ uptake was blocked by the addition of amiloride. Transepithelial current, water flow and ion fluxes were measured. A negative current was passed across the skins (the skins were clamped at –100 mV, basolateral solution was taken as reference). When PGE₂, was added to the skins under these experimental conditions, the current became more negative; this was mainly due to an increase in the Na⁺ efflux. Together with the increase in Na⁺ efflux a significant increase of the water secretion was observed. The water secretion was coupled to the efflux of Na⁺, and when one Na⁺ was pulled from the basolateral to the apical solution via this pathway 230 molecules of water follwed. From the data presented it is suggested that this pathway for Na⁺ is confined to the exocrine glands.     

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.