Net Ion Fluxes Research Articles

Ion bombardment diagnostics in a nitrogen RF magnetron sputtering discharge

Abstract The identity, fluxes and kinetic energy distributions of positive ions bombarding the substrate during radio frequency (RF) magnetron sputtering of graphite in a balanced nitrogen plasma have been investigated for various settings of discharge power and pressure by using energy-mass spectrometry analysis and probe measurements. Three prominent groups of ionic species were identified to form the ion bombardment. The first is due to the process gas ions, of which the primary ions of nitrogen are the dominant ones. The two further ionic groups are clearly related to sputtered carbon and its reaction products with nitrogen. The net fluxes of these ionic species respond very sensitively to changes in the discharge conditions. The ratios of the net ion fluxes of C + and N + to their atom deposition rates indicate that nearly all carbon species for film growth arise from the arriving flux of sputtered C atoms, whereas the bombarding N + flux acts as an intense nitrogen source for the film chemistry. The ion kinetic energy distributions measured for predominant ions, such as C + , N + , N + 2 and (CN) + 2 , were observed to be qualitatively similar in their shapes and trends, clearly reflecting the ions' sensitivity to RF modulations and to collision processes while passing the near-substrate sheath. Over the range of power and pressure, the mean kinetic energy of the bombarding ions was from about 25 eV to 45 eV. With the found data, the energy flux density of the ion bombardment and the averaged bombardment energy per condensing carbon and nitrogen atom were calculated, these being fundamental internal process parameters for judging the effect of the bombarding ion flux on carbon nitride formation.

Proton and calcium flux oscillations in the elongation region correlate with root nutation

The involvement of Ca2+ and H+ flux oscillations in root nutation was studied for decapped roots of corn (Zea mays L. cv. Aussie Gold) placed horizontally. Net ion fluxes were measured around the elongation and meristematic regions using a microelectrode ion flux measuring system. High correlation between H+ flux oscillations and root nutations was found in the elongation region. Two oscillatory components of H+ flux, with periods of about 90 min and 7 min, correlated with root circumnutations and micronutations, respectively. The periods of H+ flux oscillations and rhythmical root movements in this region could be modified similarly by external factors including pH. In the meristematic region no association between ion flux behaviour and nutation was apparent. Ion flux oscillations and nutations both decreased in amplitude as the growth rate at the measured location decreased. Possible involvement of ion flux oscillations in root circumnutation is discussed. It is concluded that a model involving an internal oscillator must be developed to explain the H+ flux involvement in root nutations.

Distribution of lactate and other ions in inactive skeletal muscle: influence of hyperkalemic lactacidosis

The purpose of this study was to quantify changes in intracellular ion and acid-base status resulting from the net flux of ions between perfusate and noncontracting muscle of differing fibre type in response to a perfusate that simulated the ionic conditions seen during intense exercise. Isolated rat hind limbs were perfused for 80 min with a bovine erythrocyte perfusate. Two series of experiments were performed: a normal perfusate (NP, n = 8) or a lactacidotic perfusate (LP, n = 8) that simulated arterial plasma and blood composition during intense exercise ([Lac-] = 11.0 mequiv. L-1, [K+] = 7.5 mequiv. L-1, and nonvolatile acid concentration = 71 nequiv.L-1). Net ion fluxes were determined by the arteriovenous difference across the hind limb and perfusate flow. Muscle ion concentrations were measured in the soleus (SOL), plantaris (PLT), and white gastrocnemius (WG) muscles. In the NP group, small net effluxes of K+ and Lac- from muscle were observed, but there was no net flux of Na+ or CI-. During LP, an initial rapid net influx of Lac- into muscle (151.2 +/- 9.4 mu equiv. min-1. 100 g-1 at 5 min) was followed by a steady-state net influx of 24-37 mu equiv. min-1. 100 g-1 between 20 and 60 min. During LP, net influx of Na+, CI-, and K+ was greater than during NP and average 58.0 +/- 11.2, 30.0 +/- 7.5, and 7.5 +/- 1.9 mu equiv. min-1. 100 g-1, respectively. Following LP, muscle content of Na+ (WG only) and Lac- (WG, PLT, and SOL) was increased to a greater extent than following NP. The increased [Lac-]i contributed to an elevated [H+]i only in the slow oxidative SOL, consistent with the higher concentration of Lac- transporters, lower capacity to bind protons, and better regulation of [Na+]i in slow oxidative muscles. Calculated membrane potential (Em) was unchanged with NP but decreased on average from -76.2 +/- 1.2 to 63.4 +/- 2.2 mV with LP perfusion, with no difference among fibre types. The steady-state distribution of Lac- across the sarcolemma appears to be a function of both metabolic and transport processes; specifically, Lac- distribution was not fully explained by the membrane potential nor by the nonionic distribution of HLac as determined by the transmembrane pH gradient. It is concluded that inactive skeletal muscle modifies the ionic composition of blood perfusing the muscles. However, the altered ionic composition of these muscles may compromise their function as a result of an altered membrane potential in fast and slow muscles and increased [H+]i in slow oxidative muscles.

Thyroxine effect on intestinal Cl-/HCO3- exchange in hypo- and hyperthyroid rats.

Changes in transepithelial water and electrolyte transport as causative or contributing factors of the diarrhoea and constipation found associated with changes in thyroid physiology were studied. Albino Wistar rats were pharmacologically made either hypothyroid or hyperthyroid. After sacrifice, the small intestine was mounted in Ussing chambers in order to measure in vitro ion net fluxes under short-circuit conditions. Hypothyroid animals showed an increase in intestinal transit time, Cl- absorption (mainly due to an increment in its mucosal to serosal component) and residual ion flux (which is believed to represent HCO3- secretion) when compared with euthyroid animals. The hyperthyroid animals showed a decrease in Cl- mucosal to serosal transport. Furthermore, a significant correlation was found between serum L-thyroxine (T4) levels and both net Cl- transport (r = -0.74, P < 0.00001) and residual ion flux (r = -0.55, P < 0.005). These results indicate that the effect of T4 is firstly to inhibit Cl-/HCO3- anion exchange thereby influencing transepithelial flux transport and secondly to affect intestinal motility. Such inhibition was not found when T4 was acutely added to rat ileum, suggesting that the effect on electrolyte transport probably requires protein synthesis. In conclusion, the phenomenon observed in vitro could explain the clinical manifestations of constipation and diarrhoea in hypo- and hyper-thyroidism respectively.

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.

Calcium and Magnesium: Low Passive Permeability and Tubular Secretion in the Mouse Medullary Thick Ascending Limb of Henle's Loop (MTAL)

Recent studies from our laboratory have shown that in the mouse and rat nephron Ca2+ and Mg2+ are not reabsorbed in the medullary part of the thick ascending limb (mTAL) of Henle's loop. The aim of the present study was to investigate whether the absence of transepithelial Ca2+ and Mg2+ transport in the mouse mTAL is due to its relative low permeability to divalent cations. For this purpose, transepithelial ion net fluxes were measured by electron probe analysis in isolated perfused mouse mTAL segments, when the transepithelial potential difference (PDte.) was varied by chemical voltage clamp, during active NaCl transport inhibition by luminal furosemide. The results show that transepithelial Ca2+ and Mg2+ net fluxes in the mTAL are not driven by the transepithelial PDte. At zero voltage, a small but significant net secretion of Ca2+ into the tubular lumen was observed. With a high lumen-positive PDte generated by creating a transepithelial bath-to-lumen NaCl concentration gradient, no Ca2+ and Mg2+ reabsorption was noted; instead significant and sustained Ca2+ and Mg2+ net secretion occurred. When a lumen-positive PDte was generated in the absence of apical furosemide, but in the presence of a transepithelial bath-to-lumen NaCl concentration gradient, a huge Ca2+ net secretion and a lesser Mg2+ net secretion, not modified by ADH, were observed. Replacement of Na+ by K+ in the lumen perfusate induced, in the absence of PDte changes, important but reversible net secretions of Ca2+ and Mg2+. In conclusion, our results indicate that the passive permeability of the mouse mTAL to divalent cations is very low and not influenced by ADH. This nephron segment can secrete Ca2+ and Mg2+ into the luminal fluid under conditions which elicit large lumen-positive transepithelial potential differences. Given the impermeability of this epithelium to Ca2+ and Mg2+, the secretory processes would appear to be of cellular origin.

Effects of Polyunsaturated Fatty Acids on Bile Acid-Induced Gastric Mucosal Injury

Arachidonic acid is a polyunsaturated fatty acid precursor to prostaglandin formation in the stomach. When applied topically to gastric mucosa it prevents injury from a variety of damaging agents, similar to the effects observed with exogenous prostaglandins. Alternatively, fatty acids could act as mild irritants and protect the gastric mucosa in an adaptive cytoprotective process. This study was undertaken to ascertain whether arachidonic acid attenuates gastric injury from bile acid by acting as a mild irritant to the gastric epithelium or by increasing biosynthesis of cytoprotective prostaglandins. Accordingly, adult anesthetized rat stomachs were pretreated for 30 min with either topical 1 mMarachidonic acid, docusahexaenoic acid or eicosatrienoic acid prior to injury with topical 5 mMacidified taurocholate. In a second set of experiments using a similar protocol, the role of prostaglandins was evaluated by giving indomethacin (5 mg/kg/sc) 30 min prior to fatty acid pretreatment. Mucosal injury was assessed by measuring net transmucosal ion fluxes, the appearance of DNA into the gastric lumen, and histology. Gastric luminal PGE2content was determined by radioimmunoassay. Pretreatment with topical arachidonic acid, but not docusahexaenoic acid or eicosatrienoic acid, significantly (P< 0.05) decreased bile acid induced net luminal ion fluxes, DNA accumulation and histologic injury scores, an effect negated by indomethacin. Further, pretreatment with arachidonic acid was associated with increased luminal PGE2content, an effect also abolished by indomethacin. Thus, arachidonic acid does not act as a mild irritant, but protects the gastric mucosa from bile acid injury through a mechanism involving increased bioavailability of substrate for prostaglandin formation.

Isoproterenol-induced gastric mucosal protection from bile acid

Topical isoproterenol is a potent protective agent against bile acid-induced gastric mucosal injury in hypotensive and normotensive rats. This study was undertaken to ascertain what role endogenous prostaglandins and gastric mucosal blood flow play in isoproterenol-induced protection. Accordingly, anesthetized, fasted rats were given the cyclooxygenase inhibitor, indomethacin (5 mg/kg subcutaneously), 30 min prior to topical pretreatment with 3 ml of intragastric saline, isoproterenol (3 microM), or 16,16-dimethyl prostaglandin E2 (3 microM) for 15 min. Gastric injury was induced with topical 5 mM acidified taurocholate and damage assessed by measuring net transmucosal ion fluxes, the appearance of DNA into the gastric lumen, and histology of the gastric epithelium. In a separate set of experiments, the effects of topical isoproterenol on gastric mucosal blood flow (laser Doppler flowmetry) and luminal PGE2 concentrations (125I radioimmunoassay) were examined. Pretreatment with topical isoproterenol or 16,16-dimethyl prostaglandin E2 significantly decreased bile acid-induced net luminal ion fluxes and DNA accumulation, suggesting mucosal protection. The protective effect of isoproterenol, but not 16,16-dimethyl prostaglandin E2, was negated by indomethacin (corroborated by histology). Further, isoproterenol did not significantly alter gastric mucosal blood flow, but did augment luminal PGE2 concentrations, an effect also abolished by indomethacin. Thus, isoproterenol appears to protect the gastric mucosa from the damaging effects of bile acid through a mechanism that requires the synthesis and release of cytoprotective endogenous prostaglandins.

Estimated potassium reflection coefficient in perfused proximal convoluted tubules of the anaesthetized rat in vivo.

1. As yet there is no definitive description of the mechanism and route by which K+ reabsorption is achieved in the proximal convoluted tubule (PCT). We have assessed the contribution of convective K+ transport to net potassium ion flux (JK) by estimating the reflection coefficient of K+ (sigma K) in the proximal tubule of anaesthetized rats previously prepared for in vivo microperfusion. 2. Alterations in the luminal concentration of the impermeant solute raffinose in single-perfused (lumen only) and double-perfused (lumen and capillaries) PCTs were found to change fluid reabsorption in a predictable fashion. 3. Net potassium ion flux (JK) in single- and double-perfused tubules was significantly correlated with net fluid flux (Jv), suggesting that convective K+ transport may be a significant factor in overall K+ transport by the PCT. 4. Estimates of sigma K in single- and double-perfused tubules were very similar (0.14 +/- 0.06 and 0.13 +/- 0.05, respectively), even though K+ diffusion was not strictly controlled in the former group. The maximum effect of 'pseudo-solvent' drag in double-perfused tubules was estimated to give a sigma K of 0.40. This low value for sigma K suggests that true convection/solvent drag may be an important driving force for the reabsorption of K+ from the PCT of the rat.

Activation of Na:2Cl:K cotransport by luminal chloride in macula densa cells

Changes in macula densa intracellular pH (pHi) were used to monitor the direction of flux mediated by the apical Na:2Cl:K cotransporter. At the macula densa, a decrease in luminal [Cl] ([Cl]1) from 60 to 1 mM produced cellular alkalinization secondary to a cascade of events involving a decrease in apical Na:2Cl:K cotransport, a fall in intracellular [Na] ([Na]i) and a stimulation of Na:H exchange. This is supported by the fact that 97% of the change in macula densa pHi with reduction in [Cl]1 was bumetanide-sensitive whereas 92% of this pH change was amiloride-sensitive. We found that, in the presence of 20 mM Na and 5 mM K, a [Cl]1 of 14.3 +/- 2.4 mM (N = 7) produced equilibrium of the apical cotransporter since the pHi obtained under this condition was identical to the pHi found after reducing the net ionic flux to zero with bumetanide. Using this value together with the expected stoichiometry for the bumetanide-sensitive cotransporter, it was estimated that the intracellular [Cl] ([Cl]i) at equilibrium (or in the presence of bumetanide) could be as low as 5 mM. Also, using a Hill number of 2 which is consistent with the present data, the affinity for [Cl]1 was found to be 32.5 mM. Under physiological luminal conditions prevailing at the end of the thick ascending limb (approximately 3.5 mM K, and approximately 25 to 30 mM NaCl), macula densa cells are probably operating close to equilibrium while maintaining a small net reabsorption of Na/K and Cl. Since macula densa cells appear capable of reducing [Cl]i to very low levels, a reabsorptive flux should continue to occur until [NaCl]1 is reduced to 18 mM.

Fasting alters basal and stimulated ion transport in piglet jejunum

Three-week-old piglets were used to study the effects of short-term fasting on jejunal ion transport. A 48-h fast significantly reduced mucosal weight, villus height, and crypt depth. Fasting increased basal short-circuit current (Isc), which reflects active ion transport, and total tissue conductance (Gt) of muscle-stripped jejunal sheets mounted in Ussing chambers. Increases in Isc evoked by carbachol, serotonin, histamine, prostaglandin E2, or Escherichia coli heat-stable enterotoxin were significantly greater in the fasted piglets. Isc responses to mucosal D-glucose were also enhanced by the fast. Under basal conditions, unidirectional and net fluxes of Na+ and Cl-, as well as serosal-to-mucosal inulin fluxes, were significantly increased in fasted piglets. In fed piglets, carbachol increased net Cl- secretion by stimulating serosal-to-mucosal Cl- flux; Gt was not affected. In fasted piglets, carbachol increased net Cl- secretion by inhibiting mucosal-to-serosal fluxes with no effect on serosal-to-mucosal fluxes. In addition, carbachol significantly inhibited mucosal-to-serosal Na+ fluxes and reduced Gt in this group. Thus a 48-h fast increased unidirectional and net ion fluxes in piglet jejunum and enhanced ion transport responses to secretory agonists. The mechanism by which carbachol stimulated net Cl- secretion was also altered by the fast. These results suggest that the absence of luminal nutrition changes the ion transport characteristics of the jejunal epithelium.

Ion flow in the bath and flux interactions between channels

We present an exact solution to the linearized Nernst-Planck-Poisson equation for spherically symmetric current flow. This solution differs from Levitt's solution (Levitt, D. G. 1992. Biophys. J., Eq. A5) by its dependence on an additional parameter, which is equal to the net ion flux for monovalent ion-selective channels. For ion-selective channels, this solution may provide better boundary conditions to modelling the flow in the channel pore itself, although only at low salt concentrations. We use the solution to estimate the effects of flux interaction between closely packed channels.

In vivo ion fluxes across the gills of shore crabs, Carcinusmaenas (L.)

A method is described for studying in vivo ion exchange characteristics (ion-permeability, net, passive and active ion fluxes) in the gills of aquatic organisms. The method is based on measuring time series of medium concentrations in a closed volume containing an animal. Changes in the medium ion concentration are the result of passive and active fluxes, where passive fluxes depend on the permeability and the concentration difference between blood and medium. It is shown that permeability and active flux can be derived from the slope and the Y-intercept of the straight line obtained by autocorrelation of repetitive measurements (equally spaced in time) of medium ionic concentrations. The method may prove to be useful for characterizing the functioning of aquatic organisms in normal, or experimentally modified, environments. Examples are given considering the ion exchange parameters in shore crabs, Carcinus maenas, at various osmotic conditions and at experimentally elevated environmental CO 2 levels.

Topical Prostaglandin E 2 and Isoproterenol Reduce Bile Acid-Induced Gastric Mucosal Injury in Shocked Rats

In shocked animals, topical application of bile acids at low pH to gastric mucosa results in gross mucosal injury. Both systemic prostaglandins and isoproterenol reduce this injury, but side effects may limit their clinical usefulness. The purpose of this study was to determine the effect of topical pretreatment with isoproterenol and prostaglandin E 2 on gastric mucosal injury induced by low concentrations of bile acid in shocked and normotensive rats. Mucosal injury was assessed by measuring net transmucosal ion fluxes (H +, K +) and luminal accumulation of DNA (DNAE), a sensitive and specific indicator of gastric mucosal cell exfoliation. In this model of mucosal injury, pretreatment with prostaglandin E 2 or isoproterenol significantly and dose dependently decreased luminal hydrogen loss, potassium gain, and DNA accumulation in both shocked and normotensive animals. Thus, both topical prostaglandin E 2 and isoproterenol reduce gastric mucosal injury caused by low concentrations of bile acid in shocked and normotensive rats, findings corroborated by histology. These findings provide a physiologic basis for the possible use of these agents as prophylaxis or treatment of stress gastritis and gastroduodenal ulcer in the critically ill patient.

Characterization of esophageal desalination in the seawater eel,Anguilla japonica

To characterize mechanisms of esophageal desalination, osmotic water permeability and ion fluxes were measured in the isolated esophagus of the seawater eel. The osmotic permeability coefficient in the seawater eel esophagus was 2·10-4 cm·s-1. This value was much lower than those in tight epithelial, although the eel esophagus is a leaky epithelium with a tissue resistance of 77 ohm·cm-2. When the esophagus was bathed in normal Ringer solutions on both sides no net ion and water fluxes were observed. However, when mucosal NaCl concentration was increased by a factor of 3, Na+ und Cl- ions were transferred from mucosa to serosa (desalination). If only Na+ or Cl- concentration in the mucosal fluid was increased by a factor of 3, net Na+ and Cl- fluxes were reduced to 30–40%, indicating that 60–70% of the net Na+ and Cl- fluxes are coupled mutually. The coupled NaCl transport seems to be effective in desalting the luminal high NaCl. The remaining 30–40% of the total Na+ and Cl- fluxes seems to be due to a simple diffusion, because these components are independent of each other and follow their electrochemical gradients, and also because these fluxes remain even after treatment with NaCN or ouabain. A half of the coupled NaCl transport could be explained by a Na+/H+−Cl-/HCO 3 - double exchanger on the apical membrane of the esophageal epithelium, because mucosal amiloride and 4.4′-diisothiocyanatostilbene-2,2′-disulphonic acid inhibited the net Na+ and Cl- fluxes by approximately 30%. The other half of the coupled NaCl transport, which follows their electrochemical gradients, still remains to be explained.

Hormonal stimulation of Ca2+ and Mg2+ transport in the cortical thick ascending limb of Henle's loop of the mouse: evidence for a change in the paracellular pathway permeability

Recent studies from our laboratory have shown that in the cortical thick ascending limb of Henle's loop of the mouse (cTAL) Ca2+ and Mg2+ are reabsorbed passively, via the paracellular shunt pathway. In the present study, cellular mechanisms responsible for the hormone-stimulated Ca2+ and Mg2+ transport were investigated. Transepithelial voltages (PDte) and transepithelial ion net fluxes (JNa, JCl, JK, JCa, JMg) were measured in isolated perfused mouse cTAL segments. Whether parathyroid hormone (PTH) is able to stimulate Ca2+ and Mg2+ reabsorption when active NaCl reabsorption and thus PDte, is abolished by luminal furosemide was first tested. With symmetrical lumen and bath Ringer's solutions, no Ca2+ and Mg2+ net transport was detectable, either in the absence or in the presence of PTH. In the presence of luminal furosemide and a chemically imposed lumen-to-bath directed NaCl gradient, which generates a lumen-negative PDte, PTH slightly but significantly increased Ca2+ and Mg2+ net secretion. In the presence of luminal furosemide and a chemically imposed bath-to-lumen-directed NaCl gradient, which generates a lumen-positive PDte, PTH slightly but significantly increased Ca2+ and Mg2+ net reabsorption. In view of the observed small effect of PTH on passive Ca2+ and Mg2+ movement, a possible interference of furosemide with the hormonal response was considered. To investigate this possibility, Ca2+ and Mg2+ transport was first stimulated with PTH in tubules under control conditions. Then active NaCl reabsorption was abolished by furosemide and the effect of PTH on JCa and JMg measured. In the absence of PDte and under symmetrical conditions, no Ca2+ and Mg2+ transport was detectable, either in the presence or absence of PTH. In the presence of a bath-to-lumen-directed NaCl gradient, Ca2+ and Mg2+ reabsorption was significantly higher in the presence than in the absence of PTH. Finally, when active NaCl transport was not inhibited by furosemide, but reduced by a bath-to-lumen-directed NaCl gradient, PTH strongly increased JCa and JMg, whereas only a small increase in PDte was noted. In conclusion, these data suggest that PTH exerts a dual action on Ca2+ and Mg2+ transport in the mouse cTAL by increasing the transepithelial driving force for Ca2+ and Mg2+ reabsorption through hormone-mediated PDte alterations and by modifying the passive permeability for Ca2+ and Mg2+ of the epithelium, very probably at the level of the paracellular shunt pathway.

Transepithelial Ca2+ and Mg2+ transport in the cortical thick ascending limb of Henle's loop of the mouse is a voltage-dependent process.

The mechanisms responsible for transepithelial Ca2+ and Mg2+ in transport in the isolated perfused cortical thick ascending limb (cTAL) of Henle's loop of the mouse nephron were investigated by measuring transepithelial voltages (PDte) and transepithelial ion net fluxes (JNa, JCl, JK, JCa, JMg) by electron microprobe analysis. In the presence of furosemide (10(-4) mol.l-1, lumen) and diphenylamine-2-carboxylate (DPC, 10(-4) mol.l-1, bath), known inhibitors of NaCl reabsorption in the TAL, Ca2+ and Mg2+ reabsorption was completely inhibited. In the presence of furosemide, JCa fell from 0.75 +/- 0.07 to -0.08 +/- 0.09 pmol.min-1.mm-1 (n = 5), and JMg from 0.47 +/- 0.04 to -0.01 +/- 0.11 pmol.min-1.mm-1 (n = 5). In the presence of DPC, JCa fell from 0.57 +/- 0.08 to -0.07 +/- 0.11 pmol.min-1.mm-1 (n = 5), and JMg from 0.16 +/- 0.02 to -0.11 +/- 0.07 pmol.min-1.mm-1 (n = 5). With furosemide, inhibition of Ca2+ and Mg2+ transport was paralleled by a 93% inhibition of NaCl reabsorption, while in the presence of DPC there was a 60% reduction of NaCl reabsorption. These effects were fully reversed after removal of the inhibitors from the lumen or bath solutions. In the absence of active NaCl transport, a lumen-to-bath directed-NaCl gradient (lumen: 150 mM NaCl + furosemide, bath: 50 mM NaCl + 200 mM mannitol) generated a negative transepithelial dilution potential of -13.8 +/- 1.1 mV (n = 8) which induced a significant Ca2+ and Mg2+ secretion into the tubular lumen of -0.59 +/- 0.06 and -0.43 +/- 0.05 pmol.min-1.mm-1 (n = 8), respectively. A bath-to-lumen-directed NaCl gradient, on the other hand, (lumen: 50 mM NaCl + furosemide, bath: 150 mM NaCl) generated a positive transepithelial dilution potential of +15.9 +/- 0.6 mV (n = 7), inducing a significant Ca2+ and Mg2+ reabsorption of 0.62 +/- 0.08 and 0.38 +/- 0.07 pmol.min-1.mm-1 (n = 7), respectively. Linear regression analysis of individual Ca2+ and Mg2+ net flux data versus voltage indicated that JCa and JMg were highly correlated to PDte. In conclusion, these data indicate that transepithelial Ca2+ and Mg2+ reabsorption in the mouse cTAL is predominantly a passive process, driven by the lumen-positive PDte.

Selective lipoxygenase inhibitor reduces bile acid-induced gastric mucosal injury

Leukotriene receptor blockade attenuates topical bile acid-induced gastric mucosal injury, suggesting that peptidyl-leukotrienes may be mediators of this injury. The purpose of this study was to test the hypothesis that a selective 5-lipoxygenase inhibitor protects against bile acid-induced gastric epithelial injury in the rat. Prior to injury with 10 and 20 m M acidified taurocholate (pH 1.2), rat stomachs were pretreated with either vehicle or WY50295K (selective 5-lipoxygenase inhibitor, 20 mg/kg). Injury was assessed by measuring net transmucosal hydrogen ion flux, luminal appearance of DNA, and gross mucosal injury. Topical 5-lipoxygenase inhibitor significantly reduced luminal H + ion loss, surface epithelial cell loss (as measured by luminal accumulation of DNA), and gross mucosal injury in bile acid-injured stomachs compared to controls. This study lends further support to the hypothesis that leukotrienes may be mediators of bile acid-induced gastric mucosal injury.

Altered Na+ and Cl? flux during diet-induced mixed gallstone formation in the prairie dog

Recent studies suggest that altered gallbladder absorptive function may be an important and previously unrecognized factor in the pathogenesis of experimentally induced gallstones. The present study was designed to define the specific changes in gallbladder epithelial ion transport that occur during mixed gallstone formation. Fifteen prairie dogs were fed either control or corn-alfalfa chow for six months. No control animals developed gallstones or crystals. Three of eight corn-alfalfa-fed animals had large black stones, and the remaining five had crystals ("pregallstone" group). Corn-alfalfa-fed animals had significant increases in gallbladder bile cholesterol, phospholipids, and calcium as compared to controls. Gallbladders were removed and mounted in a Ussing chamber for electrophysiologic and ion flux studies. Gallbladders from animals fed corn-alfalfa demonstrated significant decreases in short-circuit current and potential difference as compared to controls (P less than 0.05). 22Na and 36Cl were used to determine unidirectional ion fluxes. While net ion fluxes were similar in pregallstone animals and controls, stone-forming animals exhibited a significant decrease in net Na+ flux and a significant reversal in the direction of net Cl- flux (from secretion to absorption) as compared to controls (P less than 0.05). These data indicate that mixed gallstone formation is associated with alterations in gallbladder ion transport. The role of these changes in the pathogenesis of mixed gallstones remains to be determined.

Do sensory neurons mediate adaptive cytoprotection of gastric mucosa against bile acid injury?

Pretreatment with the mild irritant 1 mmol acidified taurocholate protects the gastric mucosa from the injury induced by the subsequent application of 5 mmol acidified taurocholate, a phenomenon referred to as “adaptive cytoprotection.” How this occurs remains an enigma. The purpose of this study was to investigate the role of sensory neurons and mucus secretion in this phenomenon. Prior to injury with 5 mmol acidified taurocholate (pH 1.2), the stomachs of six groups of rats were subjected to the following protocol. Two groups were topically pretreated with either saline or the mild irritant 1 mmol acidified taurocholate. Two other groups received the topical anesthetic 1% lidocaine prior to pretreatment with either saline or 1 mmol acidified taurocholate. The last two groups got the mucolytic agent 10% N-acetylcysteine (NAC) after pretreatment with either saline or 1 mmol acidified taurocholate. Injury was assessed by measuring net transmucosal ion fluxes, luminal appearance of deoxyribonucleic acid (DNA), and gross and histologic injury. Pretreatment with the mild irritant 1 mmol acidified taurocholate significantly decreased bile acid-induced luminal ion fluxes and DNA accumulation, suggesting mucosal protection (corroborated by gross and histologic injury analysis). This effect was negated by lidocaine but not by NAC. Thus, it appears that sensory neurons, and not increased mucus secretion, play a critical role in adaptive cytoprotection.