Net Sodium Flux Research Articles

The Sodium Concentration of Enteral Diets Does Not Influence Absorption of Nutrients but Induces Intestinal Secretion of Water in Miniature Pigs

Contradictory opinions exist as to whether the sodium concentration of enteral diets influences absorption of macronutrients and transepithelial movement of sodium and water. Therefore, we investigated the effects of various sodium concentrations of enteral diets on absorption of macronutrients and on net fluxes of sodium and water. In unanesthetized miniature pigs, a 150-cm jejunal segment was perfused with an oligopeptide (Peptisorb), an oligomeric and a polymeric diet. The polymeric diet was supplemented with pancreatic enzymes. The sodium concentrations varied between 30 and 150 mmol/L. The energy density was 3.4 MJ/L. The sodium concentration of the diets did not influence absorption of macronutrients and of total energy. However, increasing sodium concentrations of the diets were associated with increasing osmolality of the solutions, resulting in a linear increase in net secretion of water and flow rate of chyme. With all diets and sodium concentrations net secretion of sodium occurred. The sodium secretion was independent of the initial sodium concentration of the diets. It was linearly correlated with net flux of water and was largest in miniature pigs infused with the oligomeric diet. The sodium concentration of the jejunal effluent did not correspond to the initial sodium concentration of the diets. The present results indicate that enteral feeding of diets with high energy density inevitably increases net secretion of water and sodium as sodium concentration increases. Therefore, the sodium concentration of diets should be as low as possible to meet only the minimal daily requirement of sodium. Low sodium concentrations of diets have no negative effects on absorption of macronutrients.

Comparative Effect of Nitrogen Forms on Nitrogen Uptake and Cotton Growth Under Salinity Stress

The effects of nitrogen (N) forms (ammonium- or nitrate-N) on plant growth under salinity stress [150 mmol sodium chloride (NaCl)] were studied in hydroponically cultured cotton. Net fluxes of sodium (Na+), ammonium (NH4+), and nitrate (NO3−) were also determined using the Non-Invasive Micro-Test Technology. Plant growth was impaired under salinity stress, but nitrate-fed plants were less sensitive to salinity than ammonium-fed plants due mainly to superior root growth by the nitrate-fed plants. The root length, root surface area, root volume, and root viability of seedlings treated with NO3-N were greater than those treated with NH4-N with or without salinity stress. Under salinity stress, the Na+ content of seedlings treated with NO3-N was lower than that in seedlings treated with NH4-N owing to higher root Na+ efflux. A lower net NO3− efflux was observed in roots of nitrate-fed plants relative to the net NH4+ efflux from roots of ammonium-fed plants. This resulted in much more nitrogen accumulation in different tissues, especially in leaves, thereby enhancing photosynthesis in nitrate-fed plants under salinity stress. Nitrate-N is superior to ammonium-N based on nitrogen uptake and cotton growth under salinity stress.

Prenatal programming of rat cortical collecting tubule sodium transport

Prenatal insults have been shown to lead to elevated blood pressure in offspring when they are studied as adults. Prenatal administration of dexamethasone and dietary protein deprivation have demonstrated that there is an increase in transporter abundance for a number of nephron segments but not the subunits of the epithelial sodium channel (ENaC) in the cortical collecting duct. Recent studies have shown that aldosterone is elevated in offspring of protein-deprived mothers when studied as adults, but the physiological importance of the increase in serum aldosterone is unknown. As an indirect measure of ENaC activity, we compared the natriuretic response to benzamil in offspring of mothers who ate a low-protein diet (6%) with those who ate a normal diet (20%) for the last half of pregnancy. The natriuretic response to benzamil was greater in the 6% group (821.1 ± 161.0 μmol/24 h) compared with the 20% group (279.1 ± 137.0 μmol/24 h), consistent with greater ENaC activity in vivo (P < 0.05). In this study, we also directly studied cortical collecting tubule function from adult rats using in vitro microperfusion. There was no difference in basal or vasopressin-stimulated osmotic water permeability. However, while cortical collecting ducts of adult offspring whose mothers ate a 20% protein diet had no sodium transport (-1.9 ± 3.1 pmol·mm(-1)·min(-1)), the offspring of rats that ate a 6% protein diet during the last half of pregnancy had a net sodium flux of 10.7 ± 2.6 pmol·mm(-1)·min(-1) (P = 0.01) in tubules perfused in vitro. Sodium transport was measured using ion-selective electrodes, a novel technique allowing measurement of sodium in nanoliter quantities of fluid. Thus we directly demonstrate that there is prenatal programming of cortical collecting duct sodium transport.

Vasopressin-dependent coupling between sodium transport and water flow in a mouse cortical collecting duct cell line

Water balance is achieved through the ability of the kidney to control water reabsorption in the connecting tubule and the collecting duct. In a mouse cortical collecting duct cell line (mCCD(c11)), physiological concentrations of arginine vasopressin increased both electrogenic, amiloride-sensitive, epithelial sodium channel (ENaC)-mediated sodium transport measured by the short-circuit current (Isc) method and water flow (Jv apical to basal) measured by gravimetry with similar activation coefficient K(1/2) (6 and 12 pM, respectively). Jv increased linearly according to the osmotic gradient across the monolayer. A small but highly significant Jv was also measured under isoosmotic conditions. To test the coupling between sodium reabsorption and water flow, mCCD(c11) cells were treated for 24 h under isoosmotic condition with either diluent, amiloride, vasopressin or vasopressin and amiloride. Isc, Jv, and net chemical sodium fluxes were measured across the same monolayers. Around 30% of baseline and 50% of vasopressin-induced water flow is coupled to an amiloride-sensitive, ENaC-mediated, electrogenic sodium transport, whereas the remaining flow is coupled to an amiloride-insensitive, nonelectrogenic sodium transport mediated by an unknown electroneutral transporter. The mCCD(c11) cell line is a first example of a mammalian tight epithelium allowing quantitative study of the coupling between sodium and water transport. Our data are consistent with the 'near isoosmotic' fluid transport model.

Net sodium fluxes change significantly at anatomically distinct root zones of rice ( Oryza sativa L.) seedlings

Casparian bands of endodermis and exodermis play crucial roles in blocking apoplastic movement of ions and water into the stele of roots through the cortex. These apoplastic barriers differ considerably in structure and function along the developing root. The present study assessed net Na + fluxes in anatomically distinct root zones of rice seedlings and analyzed parts of individual roots showing different Na + uptake. The results indicated that anatomically distinct root zones contributed differently to the overall uptake of Na +. The average Na + uptake in root zones in which Casparian bands of the endo- and exo-dermis were interrupted by initiating lateral root primordia (root zone III) was significantly greater than that at the root apex, where Casparian bands were not yet formed (root zone I), or in the region where endo- and exo-dermis with Casparian bands were well developed (root zone II). The measurement of net Na + fluxes using a non-invasive scanning ion-selective electrode technique (SIET) demonstrated that net Na + flux varied significantly in different positions along developing rice roots, and a net Na + influx was obvious at the base of young lateral root primordia. Since sodium fluxes changed significantly along developing roots of rice seedlings, we suggest that the significantly distinct net Na + flux profile may be attributed to different apoplastic permeability due to lateral root primordia development for non-selective apoplastic bypass of ions along the apoplast.

P.3.c.039 Effects of neuroleptic treatment on oxidative stress parameters in schizophrenia patients

To clarify whether the epithelium of the human urinary tract possesses an active transepithelial sodium transport, the unidirectional sodium fluxes and the electrical parameters of the epithelium were determined on isolated pieces of renal pelvis. The epithelium was incubated in isotonic Ringer’s solution at 37.3C in Ussing-type chambers. The transepithelial potential difference was found to be 15.8 ± 3.0 mV and the transepithelial electrical resistance 760 ± 48Ω.-cm.−2. The transepithelial, unidirectional sodium fluxes were measured under short-circuit conditions. From both the unidirectional sodium influx from the luminal to the serosal side (7.01 ± 2.17) and from the efflux in the opposite direction (0.45 ± 0.07) a transepithelial sodium net flux of 6.56 ± 2.20 nmol. · minutes−1 · cm.−2 was calculated. Since there are no passive forces across the epithelium under short circuited conditions to explain the net flux, an active sodium transport has to be postulated. In all experiments, the simultaneously measured short circuit current (6.43 ± 2.18 nmol. · minutes−1·cm.−2) was not significantly different from the net sodium flux, and can therefore be taken as a measure of the net flux.

On the mechanism of sodium-proton exchange in crayfish

In salt depleted crayfish net sodium and proton fluxes were coupled 1:1 as required by the frog skin–turtle bladder model. In addition, three proton pump inhibitors produced equal reductions of both fluxes. It is concluded that the model operates in these animals. Net Na + and H + fluxes were very small in tap water adapted animals, but regression analysis clearly showed that they were coupled, though perhaps not 1:1. Proton pump inhibitors, at concentrations that suppressed ++++fluxes in salt-depleted crayfish, had no measureable effect on proton movement in tap water-adapted animals. Two of them (dicyclocarbodiimide and N-ethyl maleimide), caused a small reduction in Na + influx without affecting proton efflux. These experiments provide no support for operation of the frog–turtle system in adult crayfish adapted to tap water. A 2Na + — H + exchanger is considered from an energetic point of view. Such a system might be able to couple Na + and H + fluxes in dilute, near neutral solutions ([Na +]∼1–2 mM; pH 7).

A Chloride-Activated Na +/HCO 3−-Coupled Transport Activity in Corneal Endothelial Membranes

Investigations of corneal endothelium were made to resolve the apparent contradiction of the presence of sodium/bicarbonate cotransporter (NBC) in fresh and cultured cells and NBC’s reported absence in isolated plasma membrane vesicles. Gradient-driven ion fluxes into the vesicles were measured. Short-term incubations (0–30 s) showed the presence of a bicarbonate-dependent inward sodium flux (BDSF), which was active when the insides of the vesicles were preloaded with chloride ions. The BDSF was absent if chloride was present only externally to the vesicles. Chloride at concentrations between 30 and 40 mM inside the vesicle had its maximum effect on BDSF. Other anions (acetate, thiocyanate, or gluconate) inside the vesicles did not mimic the chloride effect. Associated with the net inward sodium flux was a net inward bicarbonate flux. Hill plots of sodium influx with respect to external bicarbonate concentrations indicated that the stoichiometry of the net transfer was 1.7 ± 0.2 (mean ± standard error, n = 5) bicarbonate ions for each sodium ion transported. There was no net chloride flux found across the membrane vesicles. The finding of a novel chloride-activated NBC activity fully resolves the apparent contradiction between whole-cell and membrane vesicle preparations.

Inflammatory cytokines alter human gallbladder epithelial cell absorption/secretion

Gallbladder inflammation is an early feature of gallstone formation in animal models. The inflammatory response is associated with increases in myeloperoxidase and interleukin (IL)-1 activities in the gallbladder wall. The present studies were designed to determine whether inflammatory cytokines directly affect gallbladder epithelial cell absorptive function. Studies were performed using cultured human gallbladder epithelial cells derived from a well-differentiated gallbladder carcinoma. Confluent monolayers were exposed to interleukin-1 (IL-1α), IL-1α plus its specific receptor inhibitor IL-1ra, tumor necrosis factor (TNF-α), lipopolysaccharide, or prostaglandin E 2. Unidirectional sodium and chloride fluxes were measured and used to calculate net ion fluxes. Compared to control monolayers, lipopolysaccharide, prostaglandin E 2, IL-1α, and TNF-α decreased mucosal-to-serosal and net sodium and chloride fluxes and increased serosal-to-mucosal movement ofsodium and un measured ions. The effects of IL-1α were completely inhibited by its specific receptor antagonist IL-1ra. Similar to the proinflammatory agents lipopolysaccharide and prostaglandin E 2, the inflammatory cytokines IL-1α and TNF-α directly affected gallbladder epithelial cell absorptive function. Because normal gallbladder absorptive function is protective against gallstone formation, alterations in absorptive function due to inflammation in the gallbladder wall may play a role in gallstone pathogenesis.

Regulatory role of cAMP in transport of Na+, Cl- and short-chain fatty acids across sheep ruminal epithelium.

Sodium is absorbed in considerable amounts across the ruminal epithelium, whilst its transport is strongly interrelated with the permeation of chloride and short-chain fatty acids (SCFAs). However, regulation of ruminal Na+, Cl-, and SCFA absorption is hardly understood. The present study was therefore performed to characterize the influence of cAMP on sodium and sodium-coupled transport mechanisms in short-circuited, stripped ruminal epithelia of sheep. Elevation of intracellular cAMP concentrations by theophylline (10 mM) or theophylline in combination with forskolin (0.1 mM) significantly reduced mucosal-to-serosal sodium transport, leading to a reduction of net transport. The theophylline- or theophylline-forskolin-induced reduction of sodium transport was accompanied by a decrease in chloride net transport but revealed no effect on propionate flux. Short-chain fatty acids stimulated Na+ transport but their stimulatory effect was almost completely blocked by theophylline-forskolin. In solutions with and without SCFAs, the inhibitory effect of 1 mM amiloride on sodium transport was strongly reduced after theophylline-forskolin pretreatment of the tissues. Blocking the production of endogenous prostaglandins by addition of indomethacin (10 microM) led to a theophylline-sensitive stimulation of unidirectional and net fluxes of sodium. The findings indicate that apical, amiloride-sensitive Na+-H+ exchange and/or basolateral Na+-K+-ATPase can effectively be blocked by cAMP, leading to a decrease in sodium and chloride transport. In the ruminal epithelium, cAMP is a second messenger of prostaglandins, which are released spontaneously under in vitro conditions.

Regulatory role of cAMP in transport of Na+, Cl- and short-chain fatty acids across sheep ruminal epithelium

Sodium is absorbed in considerable amounts across the ruminal epithelium, whilst its transport is strongly interrelated with the permeation of chloride and short-chain fatty acids (SCFAs). However, regulation of ruminal Na+, Cl-, and SCFA absorption is hardly understood. The present study was therefore performed to characterize the influence of cAMP on sodium and sodium-coupled transport mechanisms in short-circuited, stripped ruminal epithelia of sheep. Elevation of intracellular cAMP concentrations by theophylline (10 mM) or theophylline in combination with forskolin (0·1 mM) significantly reduced mucosal-to-serosal sodium transport, leading to a reduction of net transport. The theophylline- or theophylline-forskolin-induced reduction of sodium transport was accompanied by a decrease in chloride net transport but revealed no effect on propionate flux. Short-chain fatty acids stimulated Na+ transport but their stimulatory effect was almost completely blocked by theophylline-forskolin. In solutions with and without SCFAs, the inhibitory effect of 1 mM amiloride on sodium transport was strongly reduced after theophylline-forskolin pretreatment of the tissues. Blocking the production of endogenous prostaglandins by addition of indomethacin (10 µM) led to a theophylline-sensitive stimulation of unidirectional and net fluxes of sodium. The findings indicate that apical, amiloride-sensitive Na+-H+ exchange and/or basolateral Na+-K+-ATPase can effectively be blocked by cAMP, leading to a decrease in sodium and chloride transport. In the ruminal epithelium, cAMP is a second messenger of prostaglandins, which are released spontaneously under in vitro conditions.

Human amniotic fluid mathematical model: Determination and effect of intramembranous sodium flux

Objective: A recently described mathematical model of human amniotic fluid dynamics used known and estimated rates of fetal fluid production (lung liquid and urine) and composition (osmolality) to enable calculation of previously unmeasured routes of amniotic fluid resorption, including fetal swallowing and intramembranous (across the amnion) water flow. This "osmolar" model assumed that only free water resorption occurred across the intramembranous route. We hypothesized that intramembranous flow also may include solutes and electrolytes because significant concentration gradients exist between amniotic fluid and fetal plasma. We used mass balance analysis to determine the direction and magnitude of intramembranous sodium flux and to assess the ability of a newly described "sodium" model to predict changes in amniotic fluid volume in response to changes in intramembranous electrolyte flow. Mathematical modeling was used to predict changes in amniotic fluid volume in response to changes in intramembranous electrolyte flow. Study Design: Model predictions were calculated using published values for human amniotic fluid and fetal urine composition and volume. Ovine studies were used to derive lung fluid volumes and composition. Fetal swallowing and intramembranous flow were independently determined using net amniotic fluid osmolar (osmolality model) and sodium (sodium model) balance. Differences between osmolality and sodium model predictions were normalized to calculate the net intramembranous sodium flux, assuming a net balance of intramembranous osmotic solute flow. Results: Both sodium and osmolality models predicted swallowed volume to be greater than intramembranous flow until 28 to 32 weeks' gestation, after which the relationship reversed. However, the sodium model predicted greater intramembranous flow and lower swallowing rates compared with the osmolality model at all gestational ages. Osmolar mass balance required daily intramembranous sodium flux into the amniotic fluid, which increased with gestational age. Furthermore, assuming stable swallowing and intramembranous water flow, the model predicts that 5% increases or decreases in amniotic fluid solute concentrations caused by intramembranous flux result in polyhydramnios or oligohydramnios, respectively. Conclusion: Sodium and osmolality models demonstrate similarities in determinations of amniotic fluid dynamics. However, mass balance equations demonstrate a net intramembranous flow of sodium into the amniotic fluid under normal conditions. Mathematical modeling suggests that small alterations in daily intramembranous sodium flux may evoke large changes in amniotic fluid volume. (Am J Obstet Gynecol 1998;178:484-90.)

Oxyntomodulin reduces hydromineral transport through rat small intestine.

Glicentin (GLIC) and oxyntomodulin (OXM) are released from the ileum and colon during digestion. Both hormones reduce fluid and proton secretion in the stomach. The luminal concentration of sodium and chloride underlying the nutrient absorption, the effect of OXM on electrolyte transport through the small intestine, was assessed in vivo using ligated loops and in vitro using Ussing chambers. In vivo, a zero transport state, estimated by the net water, chloride, and sodium fluxes, was observed when an 80 mM NaCl normoosmolar solution (274 mosm) was administered intraluminally. Active secretion was observed with hyperosmotic challenge (474 mosm). The amplitude of this active secretion increased 2.5- to 3-fold when an electrogenic challenge (NaCl 40 mM) was substituted to the hyperosmotic one. OXM (800 fmol/ml plasma) did not modify the basal transport in the duodenum or in the jejunum (t = 45 min). When active secretion was induced by the hyperosmotic challenge, OXM (200 fmol/ml plasma) had no effect on duodenal or jejunal transport (t = 50 min). When active secretion was induced by an electrogenic challenge, OXM (300 fmol/ml plasma) preferentially reduced the hydromineral transport in jejunum. In vitro, OXM also induced a reduction in the ion transport towards the jejunal lumen (EC50 = 20 pM), the amplitude of which depended upon the integrity of the tetrodotoxin-sensitive neurons. In conclusion, OXM was able to reduce the large secretion induced in rat jejunum in vivo by an electrogenic gradient. In vitro, the antisecretory effect of OXM was partly mediated by the neurons present in the intrajejunal wall.

The body ion loss biomarker. 2. Field validation in coal mine-polluted streams

We performed a field validation of the body ion loss biomarker by developing a predictive model of the level of impact of coal mining on receiving streams. Hatchery brook charr (Salvelinus fontinalis ; wet mass = 1.25 to 32.2 g) were exposed in four mine-impacted streams that exhibited differing levels of acid and trace metals and in two unimpacted control streams. Net whole-body ion (Na, Ca) fluxes over a 4-h exposure were determined. Stepwise regression was used to develop predictive models of body ion flux over 4 h from measured stream water chemistry variables. The predictive power of the best model was assessed using cross validation. The best model predicting net sodium flux explained 48% of the variability in the model with six chemical variables (Mn, Zn, Mg, Al, Fe, and Na). The model of calcium flux explained 42% of the variation with eight variables (H + , Ca, Na, Mn, Al, Ni, Mg, and Zn). A multiple regression model derived from principal components analysis did not significantly improve the predictive power of these models. We conclude that whole-body net sodium flux and to a lesser extent whole-body net calcium flux are acute indicators of the level of impact of acid and trace metals in streams polluted by coal mine discharge and may be useful as biomarkers under field conditions.

Basal and meal-stimulated colonic absorption.

Few quantitative experiments evaluating colonic absorption of water and electrolytes have been performed using an awake, conscious animal model. The purpose of these experiments was to develop this type of model and evaluate both basal and meal-stimulated colonic absorption of water and electrolytes. Canine Thiry-Vella fistulas were created using a 20 cm segment of distal colon under general anesthesia. Colonic absorption studies were performed using infusion of the Thirty-Vella fistulas with a buffer solution containing [14C]polyethylene glycol. Electrolyte analysis and concentration of radioactivity in the effluent were obtained and used to calculate the net flux of water, sodium, and chloride. Each study consisted of an one-hour basal period and a three-hour experimental period divided into two groups. Group 1 received no meal. Group 2 orally ingested a mixed meal at the completion of the basal hour. In the basal state, water and electrolytes are absorbed from the distal colon at a steady and constant rate. An orally ingested meal produces a statistically significant increase in the rate of absorption, independent of direct colonic luminal contact with the nutrients of the meal given. These studies demonstrate an in vivo quantitative and qualitative measure of mammalian colonic water and electrolyte absorption. An increase in absorption rate occurs in response to a meal that is probably the result of an unidentified neural or humoral signal.

Effects of EGF on alveolar epithelial junctional permeability and active sodium transport.

We evaluated the effects of epidermal growth factor (EGF) on transepithelial resistance (Rt) and active ion transport by alveolar epithelial cell (AEC) monolayers on tissue culture-treated polycarbonate filters. Rat type II cells were cultured in completely defined serum-free medium (MDSF) or MDSF supplemented with EGF. The addition of EGF from either day 0 (chronic) or day 4 (subacute) resulted in significant increases in Rt and short-circuit current (ISC) on day 5. After subacute exposure, these effects were delayed in onset by 6-12 h and sustained for > 24 h. Basolateral (but not apical) EGF was responsible for these effects, which were prevented by preincubation with tyrphostin RG-50864, a reversible specific inhibitor of the EGF receptor tyrosine kinase. ISC decreased, with a sensitivity to apical inhibitors of sodium transport in the order benzamil > amiloride > 5-(N-ethyl-N-isopropyl) amiloride in MDSF +/- EGF, and was completely inhibited by the addition of basolateral ouabain. Net sodium flux and Na+, K+ -ATPase activity both increased approximately 50% in the presence of EGF. These results indicate that 1) EGF decreases tight junctional permeability and increases active sodium transport by AEC monolayers via basolaterally located EGF receptors, and 2) the pathways for AEC sodium entry and exit (+/- EGF) are apical high amiloride affinity sodium channels and basolateral sodium pumps.

Cholinergic Agents Modulate Transport in the Isolated, Perfused Ileum

The mammalian small intestine is extensively innervated by cholinergic nerve fibers, including projections to the muscular and submucosal layers. This study tested the hypothesis that cholinergic agents modulate ileal transport independent of alterations in intestinal vascular resistance and motility. Ten-centimeter segments of rabbit ileum ( n = 32) were vascularly perfused ex vivo with a physiologic electrolyte solution containing red cells. The lumen was perfused with an electrolyte solution containing [ 14C]polyethylene glycol. Net fluxes of water, sodium, and chloride were calculated during three 20-min periods: basal, drug infusion, and recovery. Agents infused at a final arterial concentration of 10 -5 mole/liter included acetylcholine, atropine, and hexamethonium. Measured perfusion pressure reflected changes in vascular resistance. Recovery calculations controlled for motility effects. Acetylcholine caused significant secretion of water, sodium, and chloride ( P < 0.05). The infusion of atropine or hexamethonium alone had no effect. Atropine but not hexamethonium prevented the prosecretory effect of acetylcholine. There were no significant changes in perfusion pressure or 14C recovery for any infused agent. Acetylcholine-induced ileal secretion is (1) mediated via atropine-sensitive muscarinic cholinergic receptors, (2) independent of extraintestinal neural pathways, and (3) independent of changes in vascular resistance or motility. These data support the hypothesis that acetylcholine influences ileal transport directly, independent of alterations in vascular resistance and motility.

Nitric oxide inhibits sodium reabsorption in the isolated perfused cortical collecting duct.

Indirect evidence suggests that nitric oxide inhibits sodium reabsorption by the collecting duct; however, direct evidence is lacking. It was hypothesized that endothelium-derived nitric oxide inhibits sodium flux in the cortical collecting duct by blocking amiloride-sensitive sodium channels. Tubules were obtained from Sprague-Dawley rats pretreated with deoxycorticosterone acetate (5 mg/rat i.m.) 5 to 9 days before the experiment. Nitric oxide was added to the system by either the addition of endothelial cells and the induction of the release of nitric oxide via acetylcholine (10(-7) M) or by the addition of nitric oxide donors. Acetylcholine-induced nitric oxide release from endothelial cells decreased lumen-to-bath sodium flux by 24 +/- 7% (N = 3; P < 0.05). The addition of the nitric oxide donor, spermine NONOate (10(-5) M), decreased net sodium flux 68% from 10.1 +/- 2.0 to 3.6 +/- 2 pmol/mm.min (N = 5; P < 0.025). To assure that the inhibition of sodium flux was due to nitric oxide, another donor, nitroglycerin (2 x 10(-5) M), was used, which decreased sodium flux by 43%. Luminal amiloride (10 microM) decreased net sodium flux by 83% (from 14.8 +/- 1.2 to 2.4 +/- 0.7 pmol/mm.min; N = 5; P < 0.025). The addition of nitric oxide via spermine NONOate to tubules decreased intracellular sodium levels by 26% (N = 6; P < 0.005). The Na(+)-K+ATPase activity of spermine NONOate-treated tubules was 14.7 +/- 3.2 pmol/mm.min compared with the control value of 10.2 +/- 2.0 pmol/mm.min. Nitroglycerin did not significantly affect pump activity either.(ABSTRACT TRUNCATED AT 250 WORDS)

Na+ and Cl- net absorption by the isolated skin of Rana esculenta.

In the last five years, several measurements of 22Na+ influx (Ji) and outflux (Jo) across symmetrical parts of the isolated skin of Rana esculenta, under permanent short circuitation, were performed in our Institute. The mean value of the 22Na+ net fluxes (Ji-Jo) exceeded the mean value of the short circuit current measurements (1.14 +/- 0.04 versus 0.98 +/- 0.02 microE.cm-2.h-1, 253 experiments). Since this discrepancy could be due to a concomitant Cl- net absorption, 36Cl- unidirectional fluxes were detected under similar experimental conditions. The Cl- net flux mean value was 0.11 +/- 0.02 microE.cm-2.h-1 (316 experiments) which accounts for 70% of the discrepancy between the Na+ net flux and short circuit current. This Cl- net absorption occurred in the absence of electrochemical gradients and was very likely maintained by a Na+/K+/2Cl- cotransport located at the outermost membrane of the epithelium. In fact bumetanide challenge (10(-5) M in the external fluid) strongly inhibited 36Cl- influx and 22Na+ influx across this tissue and cleared off the discrepancy between short circuit current and sodium net flux.

Effects of lead loads on branchial osmoregulatory mechanisms in the rainbow trout Oncorhynchus mykiss.

Exposure of rainbow trout to lead chloride (PbCl2, 1 ppm) in fresh water killed all animals within 16 days. Exposure to this lethal dose for 6 days only showed a significant increase in the haematocrit. Calcium, sodium and chloride concentrations in plasma were not notably modified. Both the influx and the net flux of sodium fluctuated much less than the diffusional water fluxes through secondary lamellae in gills. Branchial Na,K-ATPase, Ca-ATPase and HCO3-ATPase activities were not sensitive to lead toxicity. Lead caused a cellular 'wave-shaped' degeneration and renewal with modification in the number and morphology of chloride cells. Results are discussed in relation to the hydromineral balance of the trout.