Systemic lipopolysaccharide stimulates airway transepithelial Na+ transport by increasing ENaC and Na+,K+ -pump activity

1987 ◽

Vol 89 (4) ◽

pp. 563-580 ◽

Cited By ~ 7

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.

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

AJP Renal Physiology ◽

10.1152/ajprenal.1994.266.3.f367 ◽

1994 ◽

Vol 266 (3) ◽

pp. F367-F374 ◽

Cited By ~ 1

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.

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

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1976.231.6.1866 ◽

1976 ◽

Vol 231 (6) ◽

pp. 1866-1874 ◽

Cited By ~ 13

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.

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

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00580.2010 ◽

2011 ◽

Vol 301 (2) ◽

pp. R313-R319 ◽

Cited By ~ 20

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.

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