Ion transport in rat proximal colon in vivo

1986 ◽  
Vol 251 (1) ◽  
pp. G132-G139 ◽  
Author(s):  
R. Lubcke ◽  
K. Haag ◽  
E. Berger ◽  
H. Knauf ◽  
W. Gerok
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Proximal Colon ◽  
Good Evidence ◽  
Transport Processes ◽  
Disulfonic Acid ◽  
Transport Pathways ◽  
Nacl Absorption ◽  
Ion Substitution

Active Na+ absorption by the rat proximal colon in vivo is for the most part electrically silent. The rheogenic Na+ flux makes up only 8%. To elucidate the underlying transport pathways, the following experimental approaches were used: ion substitution experiments such as choline for Na+, cyclamate for Cl-, variation of luminal pH; administration of known inhibitors; and determination of changes in luminal CO2 tension and pH. The transcolonic ion fluxes as well as the electrical parameters potential difference, specific electrical resistance, and short-circuit current were monitored. Na+ transport was drastically reduced in the absence of luminal Cl-, and vice versa Cl- absorption was blocked at zero Na+. NaCl absorption was blocked by amiloride (10(-3) M) and 4-acetamido-4'-isothiocyanostilbene-2, 2'-disulfonic acid and was lowered by acetazolamide. Colonic NaCl absorption was not influenced by luminal furosemide. Na+ absorption increased with alkalinization of the luminal fluid. Tris instead of HCO-3 buffer at constant pH favored Cl- uptake. The results may easily be explained by the operation of a Na+-H+ antiport functionally coupled to a Cl(-)-HCO-3 antiport. These transport processes are supposed to be present in the columnar cells of the colonic epithelium. There is good evidence for the association of K+ secretion with rheogenic Cl- secretion by the crypt cells.

NaCl transport across equine proximal colon and the effect of endogenous prostanoids

1990 ◽  
Vol 259 (1) ◽  
pp. G62-G69 ◽  
Author(s):  
L. L. Clarke ◽  
R. A. Argenzio
Keyword(s):  
Ion Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Proximal Colon ◽  
Nacl Transport ◽  
Apparent Lack ◽  
Ussing Chambers ◽  
Cl Secretion

In contrast to in vivo findings, the equine proximal colon fails to demonstrate significant net absorption of Na+ and Cl- under in vitro conditions. The present study was undertaken to determine if endogenous prostanoids are responsible for this apparent lack of ion transport. Proximal colonic tissues from ponies were preincubated in either normal Ringer solution or in Ringer containing 1 microM indomethacin and studied in Ussing chambers containing these solutions. Untreated colonic mucosa demonstrated negligible Na(+)-Cl- absorption in the basal state. In contrast, indomethacin-treated colon significantly absorbed Na+ and Cl-, primarily as the result of an equivalent increase in the mucosal-to-serosal flux of these ions. Preincubation of proximal colon in 0.1 mM ibuprofen-treated Ringer yielded similar results. Treatment of indomethacin colon with 1 mM mucosal amiloride eliminated net Na(+)-Cl- absorption without affecting the short-circuit current (Isc). The Isc in control tissue was significantly greater than in indomethacin-treated tissue and was reduced by 0.1 mM serosal furosemide. Serosal addition of 0.1 microM prostaglandin E2 or 10 mM serosal plus mucosal theophylline to indomethacin-treated tissues abolished net Na(+)-Cl- absorption and increased the Isc to levels indistinguishable from control. In contrast, control tissues were essentially unaffected by these secretagogues. These findings indicated that Na(+)-Cl- absorption in equine proximal colon was electroneutral (possibly involving Na(+)-H+ exchange) and that the tissue was capable of electrogenic Cl- secretion. However, under the in vitro conditions, basal ion transport was dominated by endogenous prostanoids that abolished Na(+)-Cl- absorption and elicited near-maximal electrogenic Cl- secretion.

Regulation of Na-Cl absorption in rabbit proximal colon in vitro

1987 ◽  
Vol 252 (1) ◽  
pp. G45-G51 ◽  
Author(s):  
J. H. Sellin ◽  
R. De Soignie
Keyword(s):  
Ion Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Proximal Colon ◽  
Beta Agonist ◽  
Disulfonic Acid ◽  
Low Concentrations ◽  
Cotransport System ◽  
Net Flux

Ion transport in rabbit proximal colon (PC) in vitro is dominated by a Na-Cl cotransport system stimulated by epinephrine. To further characterize the regulation of Na-Cl transport, we tested the effects of specific adrenergic agonists on ion fluxes under short-circuit conditions. Additionally, we tested the effects of the transport inhibitors bumetanide, furosemide, and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS). Basal Na and Cl absorption were essentially nil [Na net flux (JNanet) = 0.3 +/- 0.4, and Cl net flux (JClnet) = -0.5 +/- 0.5 mu eq X cm-2 X h-1, means +/- SE]. The alpha 2-agonist clonidine significantly increased net Na and Cl absorption (delta JNanet = 3.0 +/- 0.6 mu eq X cm-2 X h-1, delta JClnet = 2.0 +/- 0.4 mu eq X cm-2 X h-1) with a minimal change in short-circuit current (delta Isc = 0.1 +/- 0.1 mu eq X cm-2 X h-1). The alpha 1-agonist phenylephrine and the beta-agonist isoproterenol did not alter ion transport. The alpha 2-blocker yohimbine (YOH) had a complex, concentration-dependent effect. At low concentrations (10(-6)-10(-8) M) YOH effectively inhibited epinephrine-stimulated cotransport. Compared with 10(-8)M YOH, 10(-6) YOH blocked 90% of the epinephrine-induced increases in Na and Cl absorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of short-circuit current in the in vivo perfused rat colon

1984 ◽  
Vol 246 (2) ◽  
pp. G151-G158 ◽  
Author(s):  
H. Knauf ◽  
K. Haag ◽  
R. Lubcke ◽  
E. Berger ◽  
W. Gerok
Keyword(s):  
Specific Resistance ◽  
Short Circuit ◽  
Input Resistance ◽  
Short Circuit Current ◽  
Proximal Colon ◽  
Open Circuit ◽  
Rat Colon ◽  
Length Constant

Current pulses (I) were injected into the lumen of proximal colonic segments in vivo, and the corresponding voltage deflections (delta PD) superimposed on the transcolonic PD were recorded. From the exponential decay of delta PD along the colon axis, the electrical length constant (lambda) was determined. Based on cable analysis the input resistance (= delta PD x = 0/I) and lambda made it possible to calculate the specific resistance (Rm) of the colonic epithelium as 128 +/- 16 omega X cm2. As Rm proved to be an ohmic resistor, the extrapolation from open-circuit PD (8-12 mV, lumen negative) to zero PD was feasible and made the calculation of short-circuit current (= PD/Rm) equal to 70 +/- 16 microA/cm2. In the presence of amiloride short-circuit current decreased to about 50%, whereas with theophylline it increased by about 30%. Substitution of luminal Na+ with choline or Cl- with cyclamate was associated with a marked increase of Rm. The rheogenic component of net Na+ transport was estimated to be only 8%. Electroneutral Na+ absorption functionally coupled with Cl- absorption displayed the characteristic feature of ion transport in the rat proximal colon.

Electrogenic bicarbonate secretion by prairie dog gallbladder

2007 ◽  
Vol 292 (6) ◽  
pp. G1683-G1694 ◽  
Author(s):  
A. James Moser ◽  
A. Gangopadhyay ◽  
N. A. Bradbury ◽  
K. W. Peters ◽  
R. A. Frizzell ◽  
...  
Keyword(s):  
Apical Membrane ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Impedance Analysis ◽  
Membrane Resistance ◽  
Disulfonic Acid ◽  
Prairie Dog ◽  
Anion Secretion ◽  
Ion Substitution

Pathological rates of gallbladder salt and water transport may promote the formation of cholesterol gallstones. Because prairie dogs are widely used as a model of this event, we characterized gallbladder ion transport in animals fed control chow by using electrophysiology, ion substitution, pharmacology, isotopic fluxes, impedance analysis, and molecular biology. In contrast to the electroneutral properties of rabbit and Necturus gallbladders, prairie dog gallbladders generated significant short-circuit current ( Isc; 171 ± 21 μA/cm2) and lumen-negative potential difference (−10.1 ± 1.2 mV) under basal conditions. Unidirectional radioisotopic fluxes demonstrated electroneutral NaCl absorption, whereas the residual net ion flux corresponded to Isc. In response to 2 μM forskolin, Isc exceeded 270 μA/cm2, and impedance estimates of the apical membrane resistance decreased from 200 Ω·cm2 to 13 Ω·cm2. The forskolin-induced Isc was dependent on extracellular HCO3− and was blocked by serosal 4,4′-dinitrostilben-2,2′-disulfonic acid (DNDS) and acetazolamide, whereas serosal bumetanide and Cl− ion substitution had little effect. Serosal trans-6-cyano-4-( N-ethylsulfonyl- N-methylamino)-3-hydroxy-2,2-dimethyl-chroman and Ba2+ reduced Isc, consistent with the inhibition of cAMP-dependent K+ channels. Immunoprecipitation and confocal microscopy localized cystic fibrosis transmembrane conductance regulator protein (CFTR) to the apical membrane and subapical vesicles. Consistent with serosal DNDS sensitivity, pancreatic sodium-bicarbonate cotransporter protein pNBC1 expression was localized to the basolateral membrane. We conclude that prairie dog gallbladders secrete bicarbonate through cAMP-dependent apical CFTR anion channels. Basolateral HCO3− entry is mediated by DNDS-sensitive pNBC1, and the driving force for apical anion secretion is provided by K+ channel activation.

Bioelectric properties of human cystic fibrosis and non-cystic fibrosis fetal tracheal xenografts in SCID mice

1998 ◽  
Vol 274 (4) ◽  
pp. C875-C882 ◽  
Author(s):  
Rabindra Tirouvanziam ◽  
Mama Desternes ◽  
Anouar Saari ◽  
Edith Puchelle ◽  
Bruno Péault ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Short Circuit ◽  
Severe Combined Immunodeficiency ◽  
Short Circuit Current ◽  
Transport Processes ◽  
Scid Mice ◽  
Tracheal Mucosa ◽  
Induced Changes

We measured the bioelectric properties of 14 cystic fibrosis (CF) and 33 non-CF human fetal tracheal xenografts in severe combined immunodeficiency (SCID) mice. All xenografts exhibited a mature airway-type epithelium irrespective of their gestational age, duration of engraftment, and genotype. The in vivo potential difference and the in vitro baseline short-circuit current ( I sc) were significantly higher in non-CF than in CF xenografts. In non-CF xenografts, sequential addition of amiloride, forskolin, and ATP resulted in a 39.4% decrease, a 24.1% increase, and a 43.6% increase in I sc, respectively. In CF xenografts, forskolin had no significant effect on I sc, whereas amiloride- and ATP-induced changes in I sc were proportionally higher than in non-CF xenografts (−60.0 and +68.8%, respectively). These results indicate that the bioelectric properties of non-CF xenografts are similar to those of postnatal airways and that CF xenografts exhibit lower baseline electrogenic activity than non-CF xenografts but similar regulation of ion transport processes to postnatal CF airways. This model of mature human fetal tracheal mucosa may help gain insight into early CF airway pathogenesis.

Amiloride-sensitive salt and fluid absorption in small intestine of sodium-depleted rats

1985 ◽  
Vol 248 (1) ◽  
pp. G133-G141 ◽  
Author(s):  
P. C. Will ◽  
R. N. Cortright ◽  
R. G. Groseclose ◽  
U. Hopfer
Keyword(s):  
Small Intestine ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Proximal Colon ◽  
Salt Transport ◽  
Fluid Absorption ◽  
Major Pathway

Secondary hyperaldosteronism produced by Na+ depletion was associated with increases in salt and fluid absorption in both the small intestine and the distal colon but not in the cecum and the proximal colon. Because these changes had not been documented for the small intestine, this study focused on the regulation of this tissue. Increased NaCl and water absorption was expressed in vitro by increases in short-circuit current and transepithelial potential and in vivo by increased fluid absorption and a decreased luminal content of Na+ and water. For example, the short-circuit current in the ileum of Na+-depleted rats was 2-fold that of adrenalectomized and 1.3-fold that of adrenal-intact control animals. The short-circuit current was inhibitable 24 +/- 14% by micromolar concentrations of amiloride in Na+-deficient animals compared with 1 +/- 3% in control animals. Similarly, ileal fluid absorption in vivo was 2.3-fold higher in Na+-deficient relative to control animals. The additional fluid absorption was sensitive to 50 microM amiloride, whereas amiloride had no effect in control animals. Furthermore, the Na+ content of the chyme from the ileum of Na+-deficient animals was about half that of controls. These results suggest that mineralocorticoids can induce the amiloride-sensitive Na+ transporter in the small intestine and that this type of epithelial salt transport can become a major pathway for salt retention by the small intestine.

Basolateral Cl− uptake mechanisms in Xenopus laevis lung epithelium

2010 ◽  
Vol 299 (1) ◽  
pp. R92-R100 ◽  
Author(s):  
Jens Berger ◽  
Martin Hardt ◽  
Wolfgang G. Clauss ◽  
Martin Fronius
Keyword(s):  
Xenopus Laevis ◽  
Ion Transport ◽  
Anion Exchanger ◽  
Short Circuit ◽  
Ussing Chamber ◽  
Short Circuit Current ◽  
Transport Processes ◽  
Lung Epithelium ◽  
Active Ion Transport ◽  
Uptake Mechanisms

A thin liquid layer covers the lungs of air-breathing vertebrates. Active ion transport processes via the pulmonary epithelial cells regulate the maintenance of this layer. This study focuses on basolateral Cl− uptake mechanisms in native lungs of Xenopus laevis and the involvement of the Na+/K+/2 Cl− cotransporter (NKCC) and HCO3−/Cl− anion exchanger (AE), in particular. Western blot analysis and immunofluorescence staining revealed the expression of the NKCC protein in the Xenopus lung. Ussing chamber experiments demonstrated that the NKCC inhibitors (bumetanide and furosemide) were ineffective at blocking the cotransporter under basal conditions, as well as under pharmacologically stimulated Cl−-secreting conditions (forskolin and chlorzoxazone application). However, functional evidence for the NKCC was detected by generating a transepithelial Cl− gradient. Further, we were interested in the involvement of the HCO3−/Cl− anion exchanger to transepithelial ion transport processes. Basolateral application of DIDS, an inhibitor of the AE, resulted in a significantly decreased the short-circuit current (ISC). The effect of DIDS was diminished by acetazolamide and reduced by increased external HCO3− concentrations. Cl− secretion induced by forskolin was decreased by DIDS, but this effect was abolished in the presence of HCO3−. These experiments indicate that the AE at least partially contributes to Cl− secretion. Taken together, our data show that in Xenopus lung epithelia, the AE, rather than the NKCC, is involved in basolateral Cl− uptake, which contrasts with the common model for Cl− secretion in pulmonary epithelia.

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.

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