Effect of luminal acidity on the apical cation channel in rabbit esophageal epithelium

2007 ◽  
Vol 292 (3) ◽  
pp. G796-G805 ◽  
Author(s):  
N. A. Tobey ◽  
C. M. Argote ◽  
M. S. Awayda ◽  
X. C. Vanegas ◽  
R. C. Orlando
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Acid Reflux ◽  
Cation Channel ◽  
Esophageal Epithelium ◽  
Protective Function ◽  
Membrane Area ◽  
Luminal Ph ◽  
The Impact

Esophageal epithelial cells contain an apical cation channel that actively absorbs sodium ions (Na+). Since these channels are exposed in vivo to acid reflux, we sought the impact of high acidity on Na+channel function in Ussing-chambered rabbit epithelium. Serosal nystatin abolished short-circuit current ( Isc) and luminal pH titrated from pH 7.0 to pH ≥ 2.0 had no effect on Isc. Circuit analysis at pH 2.0 showed small, but significant, increases in apical and shunt resistances. At pH < 2.0, Iscincreased whereas resistance ( RT) decreased along with an increase in fluorescein flux. The change in Isc, but not RT, was reversible at pH 7.4. Reducing pH from 7.0 to 1.1 with H2SO4gave a similar pattern but higher Iscvalues, suggesting shunt permselectivity. A 10:1 Na+gradient after nystatin increased Iscby ∼4 μAmps/cm2and this declined at pH ≤ 3.5 until it reached ∼0.0 at pH 2.0. Impedance analysis on acid-exposed (non-nystatin treated) tissues showed compensatory changes in apical (increase) and basolateral (decrease) resistance at modest luminal acidity that were poorly reversible at pH 2.0 and associated with declines in capacitance, a reflection of lower apical membrane area. In esophageal epithelium apical cation channels transport Na+at gradients as low as 10:1 but do not transport H+at gradients of 100,000:1 (luminal pH 2.0). Luminal acid also inhibits Na+transport via the channels and abolishes it at pH 2.0. These effects on the channel may serve as a protective function for esophageal epithelium exposed to acid reflux.

Effect of heat stress on rabbit esophageal epithelium

1999 ◽  
Vol 276 (6) ◽  
pp. G1322-G1330 ◽  
Author(s):  
Nelia A. Tobey ◽  
Dipali Sikka ◽  
Esteban Marten ◽  
Canan Caymaz-Bor ◽  
S. Seraj Hosseini ◽  
...  
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Transport Systems ◽  
Esophageal Disease ◽  
Esophageal Epithelium ◽  
Ussing Chambers ◽  
Epithelial Structure ◽  
Tissue Sensitivity ◽  
And Function ◽  
The Impact

Hot beverages expose the esophageal epithelium to temperatures as high as 58°C. To study the impact of such temperatures, rabbit esophageal epithelium was exposed to luminal heat or both luminal and serosal heat while mounted in Ussing chambers. Luminal heat, mimicking exposure to hot beverages, reduced potential difference (PD) and resistance ( R) when applied at ≥49°C and reduced short-circuit current ( I sc) at ≥60°C. At ≥60°C, subepithelial blisters developed. Higher temperatures reduced R only moderately and reversibly. In contrast, the I sc declined sharply and irreversibly once threshold was reached. Luminal and serosal heat also reduced PD, I sc, and R, although the threshold for reduction in I scwas now similar to that for R. Additionally, luminal and serosal heat reduced I sc more than R for any given temperature and resulted in blisters at lower temperatures (50°C) than luminal heat alone. The heat-induced decline in I sc was attributed in part to inactivation of Na-K-ATPase activity, although other transport systems could have been equally affected, and the decline in R to an increase in paracellular permeability. The latter effect on R also contributed to an increase in tissue sensitivity to luminal acid damage. Consumption of hot beverages exposes the esophagus to temperatures that can negatively impact epithelial structure and function. Impaired barrier function by heat increases the risk of esophageal damage by subsequent contact with (refluxed) gastric acid. These findings help explain in part the association between esophageal disease and consumption of hot beverages.

Research of Large-Scale Offshore Wind Farm Collection System Short Circuit Equivalent Network

2013 ◽  
Vol 448-453 ◽  
pp. 1732-1737
Author(s):  
Liu Bin ◽  
Hong Wei Cui ◽  
Li Xu ◽  
Kun Wang ◽  
Zhu Zhan ◽  
...  
Keyword(s):  
Large Scale ◽  
Wind Farm ◽  
Short Circuit ◽  
Short Circuit Current ◽  
System Optimization ◽  
Offshore Wind ◽  
Offshore Wind Farm ◽  
Collection System ◽  
Medium Voltage ◽  
The Impact

This paper analyses the characteristics of large-scale offshore wind farm collection network and the impact of the medium voltage collection system optimization,while from the electrical technology point,it proposes the short circuit current of the collection network computational model and algorithms,based on the principle of equivalent circuit.Taking a wind power coolection system planned for a certain offshore wind farm planning for example, the validity of the model and algorithm is verified.

Metabolic Support of Chloride-dependent Short-circuit Current Across Locust Rectum

1982 ◽  
Vol 99 (1) ◽  
pp. 349-362
Author(s):  
M. CHAMBERLIN ◽  
J. E. PHILLIPS
Keyword(s):  
Cyclic Amp ◽  
Short Circuit ◽  
Malpighian Tubule ◽  
Short Circuit Current ◽  
Metabolic Substrates ◽  
Endogenous Substrates ◽  
Tubule Fluid ◽  
Substrate Source ◽  
Stimulation Of

1. Recta of desert locusts were short-circuited and depleted of endogenous substrates by exposing them to saline containing cyclic AMP but no metabolites. Individual substrates were then added to substrate-depleted recta and the change in short-circuit current (Isc) monitored. 2. Proline or glucose (50 mM) caused by far the largest increase in Isc of all substrates tested. Stimulation of the Isc by proline was not dependent upon external sodium, but did require external chloride. 3. Physiological levels of proline also caused a large increase in Isc, while physiological levels of glucose produced a much smaller stimulation. Over 90% of the proline-dependent Isc stimulation can be produced by adding 15 mM proline solely to the lumen side of the tissue. 4. These results are discussed with regard to rectal oxidative metabolism and availability of metabolic substrates in vivo. High levels of proline in Malpighian tubule fluid are probably the major substrate source for rectal Cl−transport. Note:

Active transport of magnesium across the isolated midgut of Hyalophora cecropia

1975 ◽  
Vol 63 (2) ◽  
pp. 313-320
Author(s):  
J. L. Wood ◽  
A. M. Jungreis ◽  
W. R. Harvey
Keyword(s):  
Steady State ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Potassium Transport ◽  
Magnesium Concentration ◽  
Magnesium Transport ◽  
Wet Weight ◽  
Net Flux ◽  
Burk Plot

1. The 28Mg-measured net flux of magnesium from lumen-side to haemolymph-side of the isolated and short-circuited midgut was 1.97 +/− 0.28 mu-equiv cm(−2) /(−1) in 8 mM-Mg2+. 2. The magnesium-influx shows a delay before the tracer steady-state is attained, indicating the existence of a magnesium-transport pool equivalent to 6.7 mu-equiv/g wet weight of midgut tissue. 3. Magnesium depresses the short-circuit current produced the midgut but not the potassium transport, the depression being equal to the rate of magnesium transport. 4. Magnesium transport yields a linear Lineweaver-Burk plot with an apparent Km of 34 mM-Mg2+ and an apparent Vmax of 14.9 mu-equiv cm(−1) /(−1). 5. Magnesium is actively transported across the midgut and contributes to the regulation of the haemolymph magnesium concentration in vivo.

Calcium secretion in canine tracheal mucosa

1985 ◽  
Vol 59 (4) ◽  
pp. 1191-1195 ◽  
Author(s):  
F. J. Al-Bazzaz ◽  
T. Jayaram
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Open Circuit ◽  
Potential Difference ◽  
Secretory Process ◽  
Metabolic Inhibitor ◽  
Tracheal Mucosa ◽  
Transepithelial Potential ◽  
Transepithelial Potential Difference

Calcium (Ca) affects many cellular functions of the respiratory tract mucosa and might alter the viscoelastic properties of mucus. To evaluate Ca homeostasis in a respiratory epithelium we investigated transport of Ca by the canine tracheal mucosa. Mucosal tissues were mounted in Ussing-type chambers and bathed with Krebs-Henseleit solution at 37 degrees C. Unidirectional fluxes of 45Ca were determined in tissues that were matched by conductance and short-circuit current (SCC). Under short-circuit conditions there was a significant net Ca secretion of 1.82 +/- 0.36 neq . cm-2 . h-1 (mean +/- SE). Under open-circuit conditions, where the spontaneous transepithelial potential difference could attract Ca toward the lumen, net Ca secretion increased significantly to 4.40 +/- 1.14 compared with 1.54 +/- 1.17 neq . cm-2 . h-1 when the preparation was short-circuited. Addition of a metabolic inhibitor, 2,4-dinitrophenol (2 mM in the mucosal bath), decreased tissue conductance and SCC and slightly decreased the unidirectional movement of Ca from submucosa to lumen. Submucosal epinephrine (10 microM) significantly enhanced Ca secretion by 2.0 +/- 0.63 neq . cm-2 . h-1. Submucosal ouabain (0.1 mM) failed to inhibit Ca secretion. The data suggest that canine tracheal mucosa secretes Ca; this secretory process is augmented by epinephrine or by the presence of a transepithelial potential difference as found under in vivo conditions.

Active electrolyte transport in mammalian buccal mucosa

1988 ◽  
Vol 255 (3) ◽  
pp. G286-G291 ◽  
Author(s):  
R. C. Orlando ◽  
N. A. Tobey ◽  
V. J. Schreiner ◽  
R. D. Readling
Keyword(s):  
Buccal Mucosa ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Electrical Potential ◽  
Short Circuit Current ◽  
Electrolyte Transport ◽  
Electrical Potential Difference ◽  
Ussing Chambers ◽  
Net Fluxes

The transmural electrical potential difference (PD) was measured in vivo across the buccal mucosa of humans and experimental animals. Mean PD was -31 +/- 2 mV in humans, -34 +/- 2 mV in dogs, -39 +/- 2 mV in rabbits, and -18 +/- 1 mV in hamsters. The mechanisms responsible for this PD were explored in Ussing chambers using dog buccal mucosa. After equilibration, mean PD was -16 +/- 2 mV, short-circuit current (Isc) was 15 +/- 1 microA/cm2, and resistance was 1,090 +/- 100 omega.cm2, the latter indicating an electrically "tight" tissue. Fluxes of [14C]mannitol, a marker of paracellular permeability, varied directly with tissue conductance. The net fluxes of 22Na and 36Cl were +0.21 +/- 0.05 and -0.04 +/- 0.02 mueq/h.cm2, respectively, but only the Na+ flux differed significantly from zero. Isc was reduced by luminal amiloride, serosal ouabain, or by reducing luminal Na+ below 20 mM. This indicated that the Isc was determined primarily by active Na+ absorption and that Na+ traverses the apical membrane at least partly through amiloride-sensitive channels and exits across the basolateral membrane through Na+-K+-ATPase activity. We conclude that buccal mucosa is capable of active electrolyte transport and that this capacity contributes to generation of the buccal PD in vivo.

scholarly journals Further Observations on the Regulation of KCl ABSORPTION ACROSS LOCUST RECTUM

1985 ◽  
Vol 116 (1) ◽  
pp. 153-167
Author(s):  
J. W. HANRAHAN ◽  
J. E. PHILLIPS
Keyword(s):  
Chloride Transport ◽  
Short Circuit ◽  
Membrane Conductance ◽  
Short Circuit Current ◽  
Membrane Resistance ◽  
Open Circuit ◽  
High K ◽  
K Concentration ◽  
K Permeability

1. Electrophysiological and tracer flux techniques were used to studyregulation of KC1 reabsorption across locust recta. Physiologically high K+levels (100 mmolI−1) on the lumen side stimulated net 36Cl flux and reduced the theoretical energy cost of anion transport under open-circuit conductions. 2. The stimulation of short-circuit current (Ibc i.e. active C− absorption) by crude corpora cardiaca extracts (CC) was not dependent on exogenous Ca2+. Stimulations of Ibc were greatly enhanced in the presence of theophylline, indicating that the rate of synthesis of cAMP is increased by CC extracts. High CC levels lowered transepithelial resistance (Rt), suggesting that chloride transport stimulating hormone (CTSH) regulates both active Cl− absorption and counter-ion (K+) permeability. 3. High mucosal osmolarity or K+ concentration decreased Ibc and caused a disproportionately large increase in Rt, consistent with a decrease in theshunt (K+) conductance. Measurements of relative mucosal-to-serosal membrane resistance confirmed that high mucosal K+ levels reduced apical membrane conductance. Lowering mucosal pH to values observed in vivo atthe end of resorptive cycles also inhibited Ibc, apparently without affecting K+ permeability.

Analytical and Experimental Studies on Induced Current Switching by a Fault-Proof Gas Insulated Earthing Switch

2010 ◽  
Vol 11 (5) ◽  
Author(s):  
Mandava Mohana Rao ◽  
Moutusi Paul ◽  
H.S. Jain
Keyword(s):  
Short Circuit ◽  
Experimental Studies ◽  
Short Circuit Current ◽  
Design Parameters ◽  
Induced Current ◽  
Current Switching ◽  
Test Circuit ◽  
Reliable Performance ◽  
Gas Insulated Substation ◽  
The Impact

Fault-proof earthing switches are one of the important modules of a gas insulated substation, as it enables make at 100 percent short circuit current, which is functionally different from maintenance earthing switches. The fault-proof earthing switch shall be designed to make and break electro-magnetically and electro-statically induced currents as per IEC-62271-102. The paper discusses the impact of “test circuit configurations and voltage” on test parameters for gas insulated fault-proof earthing switch utilizing simulation with PSCAD software. Authors record the development of a 145 kV gas insulated fault proof earthing switch by considering novel design features like minimum arcing/pre-arcing time, effective current transfer from arcing contact to ground terminal, etc. The development has been evaluated successfully for electro-magnetically and electro-statically induced current duties as per IEC. Finally, design parameters to be considered for ensuring reliable performance during induced current switching from fault-proof earthing switches are also discussed.

Prolactin effects on ion transport across cultured mouse mammary epithelium

1981 ◽  
Vol 240 (3) ◽  
pp. C110-C115 ◽  
Author(s):  
C. A. Bisbee
Keyword(s):  
Cell Cultures ◽  
Short Circuit ◽  
Collagen Gel ◽  
Mammary Epithelium ◽  
Short Circuit Current ◽  
Sodium Absorption ◽  
Collagen Gels ◽  
Mouse Mammary Epithelium

Prolactin is a known osmoregulatory hormone in lower vertebrates, and recent evidence indicates that this hormone modulates ionic concentrations in milk. In an ultrastructurally and biochemically differentiated primary cell culture system in which mouse mammary epithelium is maintained on floating collagen gels, prolactin causes an increase in short-circuit current (Isc) of monolayers of cells derived from midpregnant (24.6 to 48.0 microA . cm-2) and lactating (10.4 to 16.1 microA . cm-2) glands. Transepithelial potential differences (basal side ground) average about -12 mV and are similar to those seen in vivo. Prelactating mammary epithelial cell cultures have transepithelial resistances ranging from 374 omega . cm2 (prolactin present) to 507 omega . cm2 (prolactin absent), and lactating cell cultures have resistances averaging almost 1,000 omega . cm2. Prolactin effects require at most one day of culture maintenance in prolactin-containing medium, and the effects are not due to known contamination of prolactin preparations with arginine vasopressin or growth hormone. Medium concentrations of prolactin as low as 1 ng/ml can elicit these effects. In prelactating cell cultures not treated with prolactin, the Isc is equal to the rate of sodium absorption. Prolactin increases sodium absorption fourfold but increases Isc only twofold. Clearly, prolactin induces other active transport; neither potassium nor chloride movements can account for this additional transport. Resistance values, current-voltage plots, and permeability coefficients indicate that in vitro mammary epithelium is a moderately “tight” tissue. Comparisons with intact glands indicate that in vitro mammary epithelium closely resembles its in vivo counterpart. Floating collagen gel cultures appear suitable for elucidating transport properties in cellularly heterogeneous and structurally complex mammalian tissues.

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