Microelectrode study of K+ accumulation by tight epithelia: II. Effect of inhibiting transepithelial Na+ transport on reaccumulation following depletion

1983 ◽  
Vol 74 (2) ◽  
pp. 155-164 ◽  
Author(s):  
Joel DeLong ◽  
Mortimer M. Civan
Keyword(s):  
Na Transport ◽  
Transepithelial Na Transport ◽  
Tight Epithelia

Use of Isolated Tight Epithelia to Study the Site and Mode of Drug Action on Cell Membrane Transport: Effect of the Antipsychotic Agent Trifluoperazine

1990 ◽  
Vol 17 (3) ◽  
pp. 224-227
Author(s):  
Henning F. Bjerregaard
Keyword(s):  
Cell Membrane ◽  
Toxic Effect ◽  
Membrane Transport ◽  
Antipsychotic Agent ◽  
Na Transport ◽  
Tight Epithelia ◽  
Acute Toxic Effect ◽  
Cell Membrane Transport ◽  
Dose Dependent ◽  
Stimulation Of

The aim of the present study was to investigate the site and mode of trifluoperazine (TFP) action on cell membrane transport by the use of isolated frog skin. This cellular system gives access to the apical (outer) and basolateral (inner) membranes of the polarised epithelial cells. Both apical and basolateral TFP addition induced a dose-dependent stimulation of Na transport, and depolarised the cellular potential. The data indicate that TFP acts by increasing the Na permeability of the apical membrane. However, the mechanisms localised in the apical and basolateral membranes are quite different. Basolateral TFP addition increased Na transport due to a stimulation of PGE2 synthesis, whereas apical TFP addition abolished Na inhibition of the apical Na channels, and thereby enhanced the Na transport. An acute toxic effect on the electrophysiological parameters was noted after addition of high apical TFP concentrations (50–100μM). This toxic effect was dependent on the presence of Na in the apical solution.

pHi determines rate of sodium transport in frog skin: results of a new method to determine pHi

1994 ◽  
Vol 266 (3) ◽  
pp. F367-F374 ◽  
Author(s):  
R. Rick
Keyword(s):  
Frog Skin ◽  
Nuclear Potential ◽  
Na Channel ◽  
Cytoplasmic Ph ◽  
Na Transport ◽  
Principal Cells ◽  
Weak Organic Acid ◽  
Transepithelial Na Transport ◽  
Cell Layers ◽  
Important Regulator

The pH of the isolated frog skin epithelium was determined on a cellular and subcellular level based on the distribution of a weak organic acid, 4-bromobenzoic acid. The indicator is detectable by X-ray microanalysis due to the presence of an element label. The results show that the pH of principal cells, but not the Na concentration, is closely correlated with the rate of transepithelial Na transport. Acidification leads to an inhibition of Na transport, regardless of whether the change was spontaneous or experimentally induced. Under the conditions of this study, the pH of principal cells was not well regulated. At a bath pH of 7.0, large pH differences between the cell layers were detectable. In mitochondria-rich cells, the pH was a function of the intracellular Cl concentration but not the Na transport rate. The cytoplasmic pH consistently exceeded the nuclear pH. The nuclear-cytoplasmic pH differential in principal cells amounted to 0.3 pH units, which is equivalent to a nuclear potential of -17 mV. The results support the view that the intracellular pH (pHi) is an important regulator of transepithelial Na transport. Regulation is primarily achieved at the level of the apical Na channel, making the Na influx the rate-limiting step in Na reabsorption.

Aldosterone and tight junctions: modulation of claudin-4 phosphorylation in renal collecting duct cells

2005 ◽  
Vol 289 (6) ◽  
pp. C1513-C1521 ◽  
Author(s):  
Cathy Le Moellic ◽  
Sheerazed Boulkroun ◽  
Daniel González-Nunez ◽  
Isabelle Dublineau ◽  
Francoise Cluzeaud ◽  
...  
Keyword(s):  
Tight Junctions ◽  
Cellular Localization ◽  
Collecting Duct ◽  
Receptor Occupancy ◽  
Paracellular Permeability ◽  
Na Transport ◽  
Charge Selectivity ◽  
Tight Epithelia ◽  
Collecting Duct Cells ◽  
Renal Collecting Duct

Aldosterone classically modulates Na transport in tight epithelia such as the renal collecting duct (CD) through the transcellular route, but it is not known whether the hormone could also affect paracellular permeability. Such permeability is controlled by tight junctions (TJ) that form a size- and charge-selective barrier. Among TJ proteins, claudin-4 has been highlighted as a key element to control paracellular charge selectivity. In RCCD2 CD cells grown on filters, we have identified novel early aldosterone effects on TJ. Endogenous claudin-4 abundance and cellular localization were unaltered by aldosterone. However, the hormone promoted rapid (within 15–20 min) and transient phosphorylation of endogenous claudin-4 on threonine residues, without affecting tyrosine or serine; this event was fully developed at 10 nM aldosterone and appeared specific for aldosterone (because it is not observed after dexamethasone treatment and it depends on mineralocorticoid receptor occupancy). Within the same delay, aldosterone also promoted an increased apical-to-basal passage of 125I (a substitute for 36Cl), whereas 22Na passage was unaffected; paracellular permeability to [3H]mannitol was also reduced. Later on (45 min), a fall in transepithelial resistance was observed. These data indicate that aldosterone modulates TJ properties in renal epithelial cells.

Transepithelial transport kinetics and Na entry in frog skin: effects of novobiocin

1976 ◽  
Vol 231 (6) ◽  
pp. 1866-1874 ◽  
Author(s):  
LJ Cruz ◽  
TU Biber
Keyword(s):  
Kinetic Parameters ◽  
Frog Skin ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Close Correlation ◽  
Transport Kinetics ◽  
Transepithelial Transport ◽  
Linear Component ◽  
Na Transport ◽  
Transepithelial Na Transport

Na+ entry across the outer surface of frog skin and transepithelial Na transport were studied simultaneously at different [Na] in either the presence or absence of novobiocin by direct measurements of J12 (unidirectional uptake) and Io (short-circuit current). J12 consisted of two components: one linear, the other saturable. The kinetic parameters of the saturating components in controls were close to the kinetic parameters of overall transepithelial transport (Jm12 = 1.68+/-0.13 mleq cm-2h-1; Io =1.80+/-0.14 mueq cm-2h-1. K12 = 6.02+/-1.27 mM;Kio=6.12+/-1.33 mM). Novobiocin significantly augmented net transepithelial Na transport by increasing J13. J31 remained unaffected. A 1:1 relationship between the saturating component of J12 and Io was observed in both treated and untreated skins at all [Na] tested. (Jm12Iom, k12, and Kio were significantly larger in treated skins, but despite very drastic changes in transport rates, a close correlation between kinetic parameters of entry step and transepithelial transport was maintained. This suggests that the kinetics of transepithelial transport may simply reflect those of the rate-limiting step: the Na entry across the outer barrier of the skin. The results indicate that the linear component of J12 is not involved in transepithelial transport kinetics.

scholarly journals Evidence for NHE3-mediated Na transport in sheep and bovine forestomach

2011 ◽  
Vol 301 (2) ◽  
pp. R313-R319 ◽  
Author(s):  
Imtiaz Rabbani ◽  
Christiane Siegling-Vlitakis ◽  
Bardhyl Noci ◽  
Holger Martens
Keyword(s):  
Ussing Chamber ◽  
Specific Inhibitor ◽  
Transepithelial Transport ◽  
Rt Pcr ◽  
Na Transport ◽  
Rumen Epithelium ◽  
Transepithelial Na Transport ◽  
High Concentrations ◽  
Chamber Studies ◽  
Nhe3 Inhibitor

Na absorption across the cornified, multilayered, and squamous rumen epithelium is mediated by electrogenic amiloride-insensitive transport and by electroneutral Na transport. High concentrations of amiloride (>100 μM) inhibit Na transport, indicating Na+/H+ exchange (NHE) activity. The underlying NHE isoform for transepithelial Na absorption was characterized by mucosal application of the specific inhibitor HOE642 for NHE1 and S3226 for NHE3 in Ussing chamber studies with isolated epithelia from bovine and sheep forestomach. S3226 (1 μM; NHE3 inhibitor) abolished electroneutral Na transport under control conditions and also the short-chain fatty acid-induced increase of Na transport via NHE. However, HOE642 (30 μM; NHE1 inhibitor) did not change Na transport rates. NHE3 was immunohistochemically localized in membranes of the upper layers toward the lumen. Expression of NHE1 and NHE3 has been previously demonstrated by RT-PCR, and earlier experiments with isolated rumen epithelial cells have shown the activity of both NHE1 and NHE3. Obviously, both isoforms are involved in the regulation of intracellular pH, pHi. However, transepithelial Na transport is only mediated by apical uptake via NHE3 in connection with extrusion of Na by the basolaterally located Na-K-ATPase. The missing involvement of NHE1 in transepithelial Na transport suggests that the proposed “job sharing” in epithelia between these two isoforms probably also applies to forestomach epithelia: NHE3 for transepithelial transport and NHE1 for, among others, pHi and volume regulation.

Mechanism of action PGE2 on active transepithelial Na transport in frog skin

1984 ◽  
Vol 27 ◽  
pp. 81
Author(s):  
S.I. Helman ◽  
T.C. Cox ◽  
W.J. Els ◽  
W. Van Driessche
Keyword(s):  
Mechanism Of Action ◽  
Frog Skin ◽  
Na Transport ◽  
Transepithelial Na Transport

scholarly journals Interaction between the basolateral K+ and apical Na+ conductances in Necturus urinary bladder.

1987 ◽  
Vol 89 (4) ◽  
pp. 563-580 ◽  
Author(s):  
J R Demarest ◽  
A L Finn
Keyword(s):  
Apical Membrane ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
K Channel ◽  
Channel Blockers ◽  
Na Transport ◽  
Transepithelial Na Transport ◽  
Pump Activity ◽  
Relationship Of

Experimental modulation of the apical membrane Na+ conductance or basolateral membrane Na+-K+ pump activity has been shown to result in parallel changes in the basolateral K+ conductance in a number of epithelia. To determine whether modulation of the basolateral K+ conductance would result in parallel changes in apical Na+ conductance and basolateral pump activity, Necturus urinary bladders stripped of serosal muscle and connective tissue were impaled through their basolateral membranes with microelectrodes in experiments that allowed rapid serosal solution changes. Exposure of the basolateral membrane to the K+ channel blockers Ba2+ (0.5 mM/liter), Cs+ (10 mM/liter), or Rb+ (10 mM/liter) increased the basolateral resistance (Rb) by greater than 75% in each case. The increases in Rb were accompanied simultaneously by significant increases in apical resistance (Ra) of greater than 20% and decreases in transepithelial Na+ transport. The increases in Ra, measured as slope resistances, cannot be attributed to nonlinearity of the I-V relationship of the apical membrane, since the measured cell membrane potentials with the K+ channel blockers present were not significantly different from those resulting from increasing serosal K+, a maneuver that did not affect Ra. Thus, blocking the K+ conductance causes a reduction in net Na+ transport by reducing K+ exit from the cell and simultaneously reducing Na+ entry into the cell. Close correlations between the calculated short-circuit current and the apical and basolateral conductances were preserved after the basolateral K+ conductance pathways had been blocked. Thus, the interaction between the basolateral and apical conductances revealed by blocking the basolateral K+ channels is part of a network of feedback relationships that normally serves to maintain cellular homeostasis during changes in the rate of transepithelial Na+ transport.

scholarly journals Regulation by aldosterone of Na+,K+-ATPase mRNAs, protein synthesis, and sodium transport in cultured kidney cells.

1987 ◽  
Vol 104 (5) ◽  
pp. 1231-1237 ◽  
Author(s):  
F Verrey ◽  
E Schaerer ◽  
P Zoerkler ◽  
M P Paccolat ◽  
K Geering ◽  
...  
Keyword(s):  
Sodium Transport ◽  
Northern Blot Analysis ◽  
Protein Biosynthesis ◽  
Relative Rate ◽  
Beta Subunit ◽  
Kidney Cells ◽  
Na Transport ◽  
Tight Epithelia ◽  
Cytoplasmic Accumulation ◽  
Specific Competitor

Transepithelial Na+ reabsorption across tight epithelia is regulated by aldosterone. Mineralocorticoids modulate the expression of a number of proteins. Na+,K+-ATPase has been identified as an aldosterone-induced protein (Geering, K., M. Girardet, C. Bron, J. P. Kraehenbuhl, and B. C. Rossier, 1982, J. Biol. Chem., 257:10338-10343). Using A6 cells (kidney of Xenopus laevis) grown on filters we demonstrated by Northern blot analysis that the induction of Na+,K+-ATPase was mainly mediated by a two- to fourfold accumulation of both alpha- and beta-subunit mRNAs. The specific competitor spironolactone decreased basal Na+ transport, Na+,K+-ATPase mRNA, and the relative rate of protein biosynthesis, and it blocked the response to aldosterone. Cycloheximide inhibited the aldosterone-dependent sodium transport but did not significantly affect the cytoplasmic accumulation of Na+,K+-ATPase mRNA induced by aldosterone.

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