Cl-free Solution Research Articles

XPS and ToF-SIMS Investigation of Native Oxides and Passive Films Formed on Nickel Alloys Containing Chromium and Molybdenum

X-ray Photoelectron Spectroscopy and Time-of-Flight Secondary Ion Mass Spectrometry were combined to characterize the surface oxides (native oxides and passive films) formed on Ni-based alloys containing chromium and molybdenum. Two alloys were studied, Ni-20Cr and Ni-20Cr-10Mo (in wt.%). For Ni-20Cr, both native oxide and passive films formed in acidic medium present a duplex structure comprising a Ni and Cr outer hydroxide layer and a Cr inner oxide layer. The Ni-20Cr-10Mo alloy presents a similar bilayer structure, but with Mo oxide located at the outer layer/inner layer interface. Cr enrichment is observed after passivation for both alloys. The corrosion resistance in acidic solution containing chlorides is enhanced by Mo, and by electrochemical pre-passivation in Cl free solution.

Effects of chlorine and carbon on Cu2ZnSnS4 thin film solar cells prepared by spray pyrolysis deposition

Cu2ZnSnS4 (CZTS) thin film solar cells were fabricated under non-vacuum conditions, wherein the absorption layer was prepared by the spray pyrolysis deposition method. By using a chlorine (Cl)-free solution instead of a Cl-containing solution, the solar cell efficiency was improved from 0.18% to 0.35%. On the CZTS surface deposited from the Cl-containing solution, Cl-containing precipitates with size of 10μm were present and were found to degrade the solar cell efficiency. The still low efficiency of 0.35% was caused by a layer containing small grains that existed between the CZTS layer and the Mo electrode, which included a significant amount of carbon. By optimizing the pre-annealing process, the small-grained layer became thinner and the efficiency was improved to 0.63%. Finally, by adjusting the chemical composition of the Cl-free solution and the CdS buffer layer deposition conditions, the cell efficiency was improved to 0.94%.

Structure and stability of cadmium chloride complexes in hydrothermal fluids

The identity and stability of aqueous species formed by cadmium in H 2O–Na/LiCl–HCl–HNO 3 solutions were investigated using in situ X-ray absorption spectroscopy (XANES and EXAFS) at 20–450 °C and 1–600 bar, combined with solubility measurements of CdO and CdS solids at 350–400 °C and 300–600 bar. Results show that aqueous Cd speciation is dominated by the cation Cd(H 2O) 6 2+ in acidic Cl-free solutions, and by chloride species CdCl m (H 2O) n 2 − m over a wide range of temperatures (20 ≤ T ≤ 450 °C), acidities (1 ≤ pH ≤ 8), and chloride concentrations (0.04 ≤ m Cl ≤ 18 mol/kg H 2O). EXAFS spectra from chloride solutions show that with increasing T and m Cl the average number of Cl atoms increases from 1 to ∼ 3 (± 0.6), accompanied by a decrease of the number of O from 6 to ∼ 1 (± 0.7), in the nearest coordination sphere around Cd. Average Cd–Cl distances in Cd complexes vary in the range 2.41–2.52 (± 0.02) Å, increasing with increasing m Cl and decreasing with increasing T, while Cd–O distances remain constant within errors at 2.30 (± 0.05) Å in the whole T and m Cl range investigated. This evolution of the Cd atomic environment is accompanied by changes in geometry of the dominant Cd–O/Cl species from octahedral-like to tetrahedral-like with increasing T and m Cl, as shown by XANES spectra analyses. These structural data are consistent with the formation of octahedral Cd(H 2O) 6 2+ and CdCl(H 2O) 5 + and tetrahedral CdCl 2(H 2O) 2 0, CdCl 3(H 2O) − and CdCl 4 − species at T ≤ 200–300 °C and m Cl ≤ 18. At T > 300 °C, aqueous Cd speciation is dominated by two complexes, CdCl 2(H 2O) 2 0 and CdCl 3(H 2O) − in a wide m Cl range (0.04–5 m). The stability constants of these complexes, derived from solubility measurements at 400 °C and 600 bar are ∼ 6 orders of magnitude higher than available HKF-model predictions based on low- T data. The new data on aqueous Cd complexes may be used for interpretation of Cd/Zn ratios measured in natural hydrothermal saline fluids and volcanic vapors in which the greater stability of Cd chloride species as compared to their Zn analogs is likely to be responsible for the elevated Cd/Zn ratios in comparison to crustal rocks and Cl-poor waters.

Low Ambient [Cl−] Increases Ca2+ Mobilization and Stimulates Nitric Oxide and Prostaglandin E2 Production in Human Bronchial Epithelial Cells

Changes in ionic composition of airway surface fluid may modulate airway epithelial functions. We tested the hypothesis that fluctuations of ambient ionic composition could affect airway epithelial Ca(2+) dynamics and Ca(2+)-dependent cellular functions, including NO release and PGE(2) production in vitro. The responses of intracellular Ca(2+) concentration ([Ca(2+)](i)) to changes in extracellular Cl(-) and Na(+ )concentrations ([Cl(-)](e), [Na(+)](e)) in the human bronchial epithelial cell line, 16HBE cells, were measured by the fura-2 method. The NO release to the medium after lowering [Cl(-)](e) was measured by an amperometric NO sensor. PGE(2) production was measured by radioimmunoassay. Changing to isotonic low [Cl(-)](e) solution by substitution with gluconate caused a sustained increase in [Ca(2+)](i) in a concentration-dependent manner, with the maximal [Ca(2+)](i) increase from the baseline level being 243 +/- 110 nM with Cl-free solution. The effect was not altered by thapsigargin but abolished by EGTA and by Cl channel blockers, including diphenylamine-2-carboxylate, disodium 4,4'-diisothiocyanatostilbene-2,2'-disulfonate, and disodium cromoglycate. In contrast, the effect of reduction of [Na(+)](e) by substitution with N-methyl-D-glucamine(+) on [Ca(2+)](i) was less than that of reduction of [Cl(-)](e). The reduction of [Cl(-)](e) caused a concentration-dependent rise in NO contents in the medium and PGE(2) production. This release of NO was inhibited by EGTA but not by dexamethasone pretreatment. These results suggest that the decrease in ambient [Cl(-)] induces Ca(2+) mobilization probably through Ca(2+) influx, followed by the release of NO and PGE(2), thereby modulating various cellular functions.

Membrane potentials in Rana temporaria muscle fibres in strongly hypertonic solutions.

Conventional microelectrode methods were used to measure variations in resting membrane potentials, E(m), of intact amphibian skeletal muscle fibres over a wide range of increased extracellular tonicities produced by inclusion of varying extracellular concentrations of sucrose. Moderate increases in extracellular tonicity to up to 2.6x normal (2.6tau) under Cl(-) free conditions produced negative shifts in E(m) that followed expectations for the K(+) Nernst equation (E(K)) applied to a perfect osmometer containing a conserved intracellular K(+) content despite any accompanying cell volume change. In contrast, E(m) remained stable in fibres studied in otherwise similar Cl(-) containing solutions, consistent with E(m) stabilization despite negative shifts in E(K) through inward cation-Cl(-) co-transport activity. Short exposures to higher tonicities (>3tau) similarly produced negative shifts in E(m) in Cl(-) free but not Cl(-) containing solutions. However, prolonged exposures to solutions of >3tau caused gradual net positive changes in E (m) in both Cl(-) containing and Cl(-) free solutions suggesting that these changes were independent of cation-Cl(-) transport. Indeed, there was no evidence of cation-Cl(-) co-transport activity in strongly hypertonic solutions despite its predicted energetic favourability, suggesting its possible regulation by E (m) in muscle. Additional findings implicated a failure to maintain greatly increased transmembrane [K(+)] gradients in these E(m) changes. Thus: (1) halving or doubling [K(+)](e) produced negative or positive shifts in E(m), respectively in isotonic or moderately hypertonic (<2.7tau), but not strongly hypertonic (>3tau) solutions; (2) subsequent restoration of isotonic extracellular conditions produced further positive changes in E(m) consistent with a dilution of the depleted [K(+)](i) by fibres regaining their original resting volumes; (3) quantitative modelling similarly predicted a gradual net efflux of K(+) as the balance between active and passive [K(+)] fluxes altered due to increased transmembrane [K(+)] gradients in hypertonic and low [K(+)](e) solutions. However, the observed positive changes in E(m) in the most strongly hypertonic solutions eventually exceeded these predictions suggesting additional limitations on Na(+)/K(+)-ATPase activity in strongly hypertonic solutions.

The Na+:Cl– Cotransporter Is Activated and Phosphorylated at the Amino-terminal Domain upon Intracellular Chloride Depletion

The renal Na(+):Cl(-) cotransporter rNCC is mutated in human disease, is the therapeutic target of thiazide-type diuretics, and is clearly involved in arterial blood pressure regulation. rNCC belongs to an electroneutral cation-coupled chloride cotransporter family (SLC12A) that has two major branches with inverse physiological functions and regulation: sodium-driven cotransporters (NCC and NKCC1/2) that mediate cellular Cl(-) influx are activated by phosphorylation, whereas potassium-driven cotransporters (KCCs) that mediate cellular Cl(-) efflux are activated by dephosphorylation. A cluster of three threonine residues at the amino-terminal domain has been implicated in the regulation of NKCC1/2 by intracellular chloride, cell volume, vasopressin, and WNK/STE-20 kinases. Nothing is known, however, about rNCC regulatory mechanisms. By using rNCC heterologous expression in Xenopus laevis oocytes, here we show that two independent intracellular chloride-depleting strategies increased rNCC activity by 3-fold. The effect of both strategies was synergistic and dose-dependent. Confocal microscopy of enhanced green fluorescent protein-tagged rNCC showed no changes in rNCC cell surface expression, whereas immunoblot analysis, using the R5-anti-NKCC1-phosphoantibody, revealed increased phosphorylation of rNCC amino-terminal domain threonine residues Thr(53) and Thr(58). Elimination of these threonines together with serine residue Ser(71) completely prevented rNCC response to intracellular chloride depletion. We conclude that rNCC is activated by a mechanism that involves amino-terminal domain phosphorylation.

Effects of endothelin-1 on epithelial ion transport in human airways.

Endothelin-1 (ET-1) exerts many biological effects in airways, including bronchoconstriction, airway mucus secretion, cell proliferation, and inflammation. We investigated the effect of ET-1 on Na absorption and Cl secretion in human bronchial epithelial cells. Addition of 10(-7) M ET-1 had no effect on the inhibition of the short circuit current (Isc) induced by amiloride, a Na channel blocker. Addition of 10(-7) M ET-1 to the apical bath in the presence of amiloride increased Isc in cultured human bronchial epithelial cells studied in Ussing chambers. No effect was observed when ET-1 was added to basolateral bath, indicating that the involved ET-1 receptors are likely present only in the apical membrane of the cells. Use of Cl-free solutions and bumetanide reduced the ET-1-induced increases in Isc, indicating that ET-1 stimulates Cl secretion. The ET-1-induced increase in Isc was prevented by exposure to the ETB receptor antagonist BQ-788 but not to the ETA receptor antagonist BQ-123. ET-1 did not raise intracellular Ca levels, but increased the intracellular concentration of cAMP. These findings indicate that ET-1 is a Cl secretagogue in human airways and acts presumably through apically located ETB receptors and activation of the cAMP pathway.

Corrosion Behaviour of Zn and Zn Alloy Coatings in Alkaline Media

SUMMARYThe corrosion behaviour of electrodeposited Zn, Zn-Co, Zn-Fe and Zn-Ni coatings without and with Chromate films was studied in alkaline solutions and mortar probes. DC polarization measurements were used for electrochemical characterization of the investigated samples, while AES XPS techniques were applied for the Chromate film analysis. The stability of the anodically formed oxide films on unchromated coatings appeared to be dependent on their composition. The oxide layer stability in Cl free NaOH solution was higher for Zn-Ni and Zn-Co alloys, while introduction of Cl ions caused lowering of stability especially for Zn-Ni coating. The detected corrosion current values implied that unchromated Zn alloys did not possess higher corrosion resistance in alkaline media containing Cl ions. Meanwhile, chromated Zn-Co coatings exhibited the beneficial effect of alloying for corrosion in alkaline solutions and concrete. A higher concentration of Cr(Vl) compounds in the passive Chromate layer of the alloyed sample may be the reason for its superior corrosion resistance.

CdTe films electrodeposited from chlorine-containing solutions

The diffusion-controlled electrodeposition process of cadmium telluride from chlorine-containing solutions of CdSO4 and the films' structure and electrical properties are studied. The effect of deposition at different temperatures (25-85 °C) and at different cathode potentials (-580 to -610 mV, versus Ag/AgCl) on the films' structure is investigated. Photo-induced current transient spectroscopy of bandgap energy levels has revealed the presence of a few shallow hole traps, which do not exist in films prepared from Cl-free solutions, and, thus, are related to chlorine/structural defect complexes. Due to the presence of the shallow hole traps, the electrical properties of these films and the charge transport mechanism in Au-CdTe devices are remarkably different from those in films deposited from Cl-free solutions. The spectral response of the photocurrent reveals a direct bandgap energy of 1.460 eV at 300 K, which is about 30 meV smaller than the bandgap in films prepared from Cl-free solutions.

Airway surface fluid volume and Cl content in cystic fibrosis and normal bronchial xenografts

We describe the use of an in vivo human bronchial xenograft model of cystic fibrosis (CF) and non-CF airways to investigate pathophysiological alterations in airway surface fluid (ASF) volume (Vs) and Cl content. Vs was calculated based on the dilution of an impermeable marker, [3H]inulin, during harvesting of ASF from xenografts with an isosmotic Cl-free solution. These calculations demonstrated that Vs in CF xenographs (28 +/- 3.0 microliter/cm2; n = 17) was significantly less than that of non-CF xenografts (35 +/- 2. 4 microliter/cm2; n = 30). The Cl concentration of ASF ([Cl]s) was determined using a solid-state AgCl electrode and adjusted for dilution during harvesting using the impermeable [3H]inulin marker. Cumulative results demonstrate small but significant elevations (P < 0.045) in [Cl]s in CF (125 +/- 4 mM; n = 27) compared with non-CF (114 +/- 4 mM; n = 48) xenografts. To investigate potential mechanisms by which CF airways may facilitate a higher level of fluid absorption yet retain slightly elevated levels of Cl, we sought to evaluate the capacity of CF and non-CF airways to absorb both 22Na and 36Cl. Two consistent findings were evident from these studies. First, in both CF and non-CF xenografts, 22Na and 36Cl were always absorbed in an equal molar ratio. Second, CF xenografts hyperabsorbed ( approximately 1.5-fold higher) both 22Na and 36Cl compared with non-CF xenografts. These results substantiate previously documented findings of elevated Na absorption in CF airways and also suggest that the slightly elevated [Cl]s found in this study of CF xenograft epithelia does not occur through a mechanism of decreased apical permeability to Cl.

Cellular site of active K absorption in the guinea-pig distal colonic epithelium.

The mammalian distal colon, which is composed of different cell types, actively transports Na, K and Cl in absorptive and K and Cl in secretory directions. To further characterize the K absorption process and to identify the cells involved in K absorption, unidirectional Rb fluxes and luminal Rb uptake into different epithelial cell types were determined in isolated guinea-pig distal colon. Net Rb absorption (1.5-2.5 micromol.h-1.cm-2) was not influenced by inhibition of Na transport with amiloride or by incubating both sides of the epithelium with Na-free solutions, but was almost completely abolished by luminal ouabain, ethoxzolamide or by incubating both sides of the epithelium with Cl-free solutions. Luminal Rb uptake, blockable by luminal ouabain, preferentially occurred in columnar surface and neck cells, to a lesser extent in surface goblet cells and to an insignificant degree in lower crypt cells. Employing a luminal Rb-Ringer (5.4 mM Rb) the Rb concentration increased within 10 min in columnar surface and neck, surface goblet and lower crypt cells to 70, 32 and about 10 mmol. kg-1 wet weight, respectively. The presence of 5.4 mM K in the luminal incubation solution reduced Rb uptake almost completely indicating a much higher acceptance of the luminal H-K-ATPase for K than for Rb. The increase in Na and decrease in K concentrations in surface and neck cells induced by luminal ouabain might indicate inhibition of the basolateral Na-K-ATPase or drastic enhancement of cellular Na uptake by the Na-H exchanger. Bilateral Na-free incubation did not alter Rb uptake, but bilateral Cl-free incubation drastically reduced it. Inhibition of net Rb absorption by ethoxzolamide and inhibition of both Rb absorption and Rb uptake by bilateral Cl-free incubation support the notion that cellular CO2 hydration is a necessary prerequisite for K absorption and that HCO3 leaves the cell via a Cl-HCO3 exchanger. Since ouabain-inhibitable transepithelial Rb flux and luminal Rb uptake rate by surface and neck cells were about the same, Rb(K) absorption seems to be accomplished mainly by columnar surface cells.

Asymmetrical Distribution of Ca-Activated Cl Channels in Xenopus Oocytes

Xenopus oocytes are a popular model system for studying Ca signaling. They endogenously express two kinds of Ca-activated Cl currents, I Cl-1 and I Cl-2. I Cl-1 is activated by Ca released from internal stores and, with appropriate voltage protocols, by Ca influx. In contrast, I Cl-2 activation is dependent on Ca influx. We are interested in understanding how these two different Cl channels are activated differently by Ca from different sources. One could hypothesize that these channels are activated differently because they are differentially localized near the corresponding Ca source. As an initial investigation of this hypothesis, we examined the distribution of I Cl-1 and I Cl-2 channels in the oocyte. We conclude that both I Cl-1 and I Cl-2 channels are primarily localized to the animal hemisphere of the oocyte, but that capacitative Ca influx occurs over the entire oocyte membrane. Evidence supporting this view includes the following observations: 1) Injection of IP 3 into the animal hemisphere produced larger and faster I Cl-1 responses than injection into the vegetal hemisphere. 2) Exposure of the animal hemisphere to Cl-free solution almost completely abolished I Cl-1 produced by IP 3-induced release of Ca from internal stores or by capacitative Ca entry. 3) Loose macropatch recording showed that both I Cl-1 and I Cl-2 currents were approximately four times and approximately three times, respectively, more dense in the animal than in the vegetal hemisphere. 4) Confocal imaging of oocytes loaded with fluorescent Ca-sensitive dyes showed that the time course of activation of I Cl-1 corresponded to the appearance of the wave of Ca release at the animal pole. 5) Ca release and Ca influx, although twofold higher in the animal pole, were evident over the entire oocyte.

HCO3-dependent pHi regulation in tracheal epithelial cells.

Regulation of intracellular pH (pHi) was studied in cultured bovine tracheal epithelial cells using microspectrofluorimetry of the fluorescent indicator 2',7'-biscarboxyethyl- 5(6)-carboxyfluorescein (BCECF). The cells, which were grown on coverslips and superfused in a chamber on the stage of a microscope, were acidified by NH4Cl-prepulses, and pHi recovery was measured (in DeltapH/min) at approximately pHi 6.7. In HCO3-free solutions the recovery rate was 0.14 pH/min, and addition of amiloride or Na-free solution reduced this rate to 0.02-0.03 pH/min. In HCO3/CO2-buffered Ringer's, the rate of recovery was 0.32 pH/min, and amiloride or Na-free reduced the rate to 0.08-0.10 pH/min. This residual Na-independent and HCO3-dependent pHi recovery was studied by using inhibitors of HCO3 and H transporters. Bafilomycin (inhibits H-ATPases) at 100 nM did not significantly affect pHi recovery, while 100 microM SCH28080 (inhibits H,K-ATPase) had a variable inhibitory effect (25-75%), indicating that a gastric-like H, K-ATPase, but not electrogenic H pump, may contribute in a minor way to the recovery from acidification. Cl-free solution and 500 microM H2DIDS (dihydro-4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid, blocks anion exchange and the outwardly rectifying Cl channel, ORCC), both blocked apparent anion exchange activity, but had no effect on the recovery; 100 microM DNDS (4-4''-dinitro-2-2'-stilbenedisulfonate blocks the ORCC but not the cystic fibrosis transmembrane conductance regulator, CFTR) had no effect on pHi recovery; DPC (diphenylamine carboxylate, blocks the CFTR and the ORCC) caused a complete and reversible inhibition of the recovery. When [K] was increased ten fold to depolarize the cell's membrane potential, the magnitude of the pHi recovery (though not the rate) was enhanced. Thus, the HCO3-dependent, Na- and Cl-independent, DPC-blockable pHi recovery may be largely due to an influx of HCO3 via CFTR Cl channels. Under physiological conditions, when the electrochemical gradient for HCO3 is likely to be outwardly rather than inwardly directed, the CFTR (or another HCO3-permeable channel) may mediate HCO3 secretion and contribute to regulation of pH of the periciliary fluid.

Regulation of renal Na-HCO3 cotransporter: III. Presence and modulation by glucocorticoids in primary cultures of the proximal tubule

We looked for the presence of the Na-HCO3 cotransporter in primary cultures of the proximal tubule and examined the modulation of this cotransporter by glucocorticoid hormones. Primary cultures of the proximal tubule of the rabbit have Cl-independent, HCO3-dependent 22Na uptake which is DIDS-sensitive. In addition, in cells loaded with BCECF and perfused with Cl-free solution, removal of Na was associated with a decrease in intracellular pH which returned to normal with re-addition of Na. The pH recovery was not inhibited by EIPA but was sensitive to DIDS. These findings are compatible with existence of Na-HCO3 cotransporter in these cells. We examined the role of glucocorticoids on the activity of the Na-HCO3 cotransporter by culturing proximal tubule cells in the presence of hydrocortisone and when confluence was reached, hydrocortisone was deleted from the medium. In the absence of hydrocortisone, the activity of the cotransporter, measured either isotopically or fluorometrically, was significantly decreased, whereas re-addition of hydrocortisone 10(-8) M, restored the activity of the cotransporter to normal levels. The effect of hydrocortisone could not be duplicated by aldosterone, suggesting a glucocorticoid-dependent effect. Dexamethasone, a glucocorticoid without mineralocorticoid activity, stimulated the activity of the cotransporter within physiologic concentrations and this effect was blocked by progesterone. The effect of dexamethasone was time-dependent and was prevented by cycloheximide, a protein synthesis inhibitor. These results demonstrate that primary cultures of the proximal tubule have Na-HCO3 cotransporter activity which is modulated by physiological concentrations of glucocorticoids through a protein synthesis-dependent mechanism.

Differential diagnosis of periodic paralysis aided by in vitro myography

In vitro twitch tests were performed on excised muscle bundles from 30 periodic paralysis (PP) patients in an attempt to verify the somatic origin of PP, and to differentiate between the hypokalemic (HypoPP) and the hyperkalemic forms (HyperPP). Seventeen PP patients with a definite diagnosis of familial HypoPP, familial HyperPP (subsequently confirmed by SCN4A mutations), or thyrotoxic PP entered the study, as well as 13 patients with a history of attacks of weakness but with negative clinical provocation tests and therefore ambiguous diagnosis; 15 normal subjects served as controls. In contrast to control, bundles from patients with clear diagnosis went into sustained paralysis on exposure to Cl-free solution. Exposure to K+ channel activators induced a large increase in force. Specifically for HypoPP muscle, low extracellular [K+] decreased twitch force which was further reduced by addition of insulin or adrenaline, whereas HyperPP bundles responded with an irreversible decrease in twitch force when extracellular [K+] was elevated. Out of the 13 patients with unclear diagnosis, the in vitro studies made it possible to classify 10 as HypoPP and one as HyperPP (later confirmed by a M1592V mutation). In the remaining two patients who claimed to suffer from paralytic attacks, all in vitro tests were normal, questioning the occurrence of dyskalemic PP. The results demonstrate that in vitro tests can be used to ensure the proper diagnosis to a high percentage when clinical provocative tests have failed.

Endogenous DHP-sensitive Ca 2+ channels in Pleurodeles oocytes

The double electrode voltage-clamp technique was used to study voltage-dependent Ca 2+ channels in Pleurodeles oocytes. From a holding potential of −80 mV, Ba-current ( I Ba) (recorded in Cl-free solution, Ba 2+ = 40 mM) activated at −36.7 ± 4 mV, peaked at −11.6 ± 4 mV and reversed at 55 ± 7 mV ( n = 24). This current activated slowly (rise time was 0.98 ± 0.2 s; n = 14 at −10 mV) and was not inactivated. Cadmium (Cd 2+, 500 μM) completely inhibited I Ba. The effect of Cd 2+ was dose-dependent (EC 50 = 37 ± 5 μM; n = 5). Moreover, I Ba was insensitive to ω-conotoxin (10 μM) but interestingly this I Ba. displayed dihydropyridine (DHP) sensitivity. Bay K 8644 (5 μM), a DHP activator, increased the peak current amplitude in a dose-dependent manner (EC 50 = 5.9 ± 0.6 μM; n = 10) and shifted the threshold and the maximum of current/voltage relationship towards negative potentials by − 10 mV. Nifedipine (5 μM), a DHP antagonist, decreased I Ba by 80% at HP of −80 mV (EC 50 = 1.2 ± 0.2 μM; n = 6). We concluded that Pleurodeles oocytes possess High-Voltage Activated Ca 2+ channels with properties similar to L-type Ca 2+ channels.

Glutamine stimulates prostaglandin-sensitive Na+-H+ exchange in experimental porcine cryptosporidiosis

Background/Aims: Recent studies of piglet cryptosporidiosis showed an injury-induced impairment of sodium-glucose cotransport and a prostaglandin-mediated inhibition of neutral NaCl absorption. Because glutamine has been shown to stimulate both neutral and electrogenic Na+ absorption, this study examined the mechanism of prostaglandin-mediated inhibition of NaCl absorption and the effect of glutamine on these processes. Methods: Ileal mucosa from control and infected pigs was mounted in Ussing chambers for flux studies or incubated with [14C]glutamine or [14C]-glucose for metabolism studies. Results: Glucose and glutamine induced equivalent increases, 2–2.5 μEq·cm−2·h−1, in Na+ absorption and short-circuit current in control ileum. Despite a reduction in villous surface area to one third of the control, glutamine enhanced both neutral and electrogenic Na+ absorption in the infected ileum by 3.5 ± 0.5 μEq·cm−2·h−1, whereas glucose was only half as effective (P < 0.05). In addition, glutamine was oxidized to CO2 at rates three times those of glucose. Indomethacin enhanced, whereas amiloride, prostaglandin E2, and Cl-free solutions inhibited the glutamine-induced neutral Na+ transport. Conclusions: Glutamine-stimulated neutral Na+ absorption is mediated by a prostaglandin-sensitive apical Na+-H+ exchange mechanism. The heightened Na+-H+ exchange and tissue oxidation of glutamine suggest that glutamine is superior to glucose for use in oral rehydration solutions.

Acetylcholine-evoked currents in juvenile mouse muscles

Single fibres were obtained from juvenile (8–12 days old) mice by enzymatic dissociation. Whole-cell voltage-clamped soleus and interosseus fibres were jet-superfused by Cl-free solutions. Current responses to ACh (0.5–50 μM) were recorded. At high [ACh], current responses in all fibres showed a transient initial and a prolonged late phase. The reversal potential of the initial phase was about 5 mV and that for the late phase about 18 mV in soleus. No difference between the reversal potentials for the two phases was seen in interosseus. At low [ACh], only the late phase was seen in soleus. Differences in reversal potentials for the two phases were found in adult interosseus fibres denervated for 10–20 days. These differences were smaller, when the pipette was attached to the endplate region, than at the fibre ends. Evidence was presented supporting the view that the diminished difference between the two reversal potentials at the endplate, mentioned above, is due to the non-uniform voltage-clamping of the membrane in the presencr of high [ACh].

A method for analysis of cellular K-transport mechanisms through thallium (201Tl) uptake in human lymphocytes.

Thallium (Tl) is the K-congener with the highest specific affinity to K-binding sites and the largest permeability in K-channels, and its usefulness for analysis of cellular K-transport mechanisms was investigated. The uptake of 201Tl was measured in cultured human lymphocytes (Jurkat cells and EBV-transformed B-cells) after various incubation conditions. In a complete culture medium the half-time of the Tl-uptake was 10 min at 37 degrees C and the steady state accumulation ratio (intracellular/extracellular) was c. 50. The steady state ouabain sensitive uptake was 81% in complete culture medium, it was reduced after substitution with Ringer solution and by a decrease in temperature (from 37 to 22 degrees C). The ouabain resistant uptake was higher at 22 degrees C than at 37 degrees C and it was almost completely inhibited in Na-free or Cl-free solution and by furosemide. The present results indicate that there are only two major routes for K-uptake in lymphocytes and that 201Tl may be a useful substitute for K in the analysis of cellular K-transport mechanisms.

Mercury Blockade of Thiazide-Sensitive NaCl Cotransport in Flounder Urinary Bladder

The effects of HgCl 2 on ion transport were investigated using isolated sheets of flounder urinary bladder, a model epithelium that is capable of electrically silent NaCl absorption and electrogenic K secretion. Exposure of the mucosal surface of the bladder to submicromolar doses of HgCl 2 reduced K secretion, but the effect was not due to blockade of apical K channels. Rather, the effects of HgCl 2 were virtually identical to those seen with experimental maneuvers that blocked the thiazide-sensitive NaCl cotransporter in the apical membrane, e.g., hydrochlorothiazide, Cl-free solutions, and Na-free solutions. Mucosal HgCl 2 also blocked 22Na absorption, suggesting that the effect of the metal was mediated by blockade of NaCl entry. The effects of HgCl 2 had a rapid onset and were readily reversed by washing, suggesting a noncovalent binding reaction. The abundance of polyanionic Hg complexes in salt solutions prompts the speculation that one of these may bind to the Cl-binding site on the cotransporter, thereby blocking it. The results provide the first evidence that the thiazide-sensitive NaCl cotransporter is a specific site of action for inorganic mercury.