Relative expression of the human epithelial Na+ channel subunits in normal and cystic fibrosis airways

1995 ◽  
Vol 269 (2) ◽  
pp. C511-C518 ◽  
Author(s):  
L. H. Burch ◽  
C. R. Talbot ◽  
M. R. Knowles ◽  
C. M. Canessa ◽  
B. C. Rossier ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Na Channel ◽  
Na Transport ◽  
Airway Epithelia ◽  
Superficial Epithelium ◽  
Steady State Levels ◽  
Alpha Beta ◽  
Cf Transmembrane Conductance Regulator ◽  
Ribonuclease Protection ◽  
Epithelial Na Channel

The availability of the newly cloned subunits (alpha, beta, gamma) of the epithelial Na+ channel (ENaC) permits molecular studies of the pathogenesis of the abnormal Na+ transport rates of cystic fibrosis (CF) airway epithelia. Northern analyses of airway epithelia showed that both normal and CF airway epithelia express ENaC subunit mRNAs in a ratio of alpha > beta > gamma. In situ hybridization studies revealed expression of all three ENaC subunits in the superficial epithelium and the alpha- and beta-subunits in the gland ductular and acinar epithelium of both normal and CF airways. Ribonuclease protection assays revealed that the steady-state levels of alpha-, beta-, and gamma-ENaC mRNAs were similar in CF and normal airway superficial epithelia. These findings indicate that 1) Na+ transport defects in CF airways disease may be expressed in glandular acinar and ductal epithelium as well as superficial epithelium, and 2) the molecular pathogenesis of Na+ hyperabsorption in CF airways does not reflect increased levels of Na+ channel mRNAs, and probably number, but reflects an absence of the normal inhibitory regulation of Na+ channels by CF transmembrane conductance regulator proteins.

Glucocorticosteroids increase sodium transport in middle ear epithelium

1997 ◽  
Vol 272 (1) ◽  
pp. C184-C190 ◽  
Author(s):  
P. Herman ◽  
C. T. Tan ◽  
T. van den Abbeele ◽  
B. Escoubet ◽  
G. Friedlander ◽  
...  
Keyword(s):  
Middle Ear ◽  
Short Circuit ◽  
Constitutive Expression ◽  
Short Circuit Current ◽  
Na Channel ◽  
Ribonuclease Protection Assay ◽  
Na Transport ◽  
Ribonuclease Protection ◽  
Dose Dependent ◽  
Epithelial Na Channel

The effect of glucocorticosteroids on ion transport was investigated on a middle ear cell line with the short-circuit current (Isc) technique. Dexamethasone (DXM) produced a dose- and time-dependent increase in Isc. Concentration of half-maximal stimulation was 2.68 x 10(-8) M. This effect was blunted by the glucocorticoid antagonist RU-38486 and was related to Na+ transport, as evidenced by the inhibition induced by 1) apical addition of the Na+ channel inhibitor benzamil (10(-6) M) or 2) substitution of Na+ with N-methylglucamine in the incubation medium. The increase in Na+ transport resulted from a primary modulation of apical Na+ entry, since 1) the Na(+)-K(+)-ATPase activity of cellular homogenates was not modified by corticosteroids and 2) the DXM-induced increase in the ouabain-sensitive uptake of 86Rb was blunted by benzamil. Ribonuclease protection assay revealed 1) a constitutive expression of the mRNA encoding the alpha-subunit of the epithelial Na+ channel and 2) that DXM increased the expression of this transcript. This increase was dose dependent and paralleled changes in transepithelial Na+ transport. This study suggests that a component of the beneficial effect of steroid therapy for the treatment of otitis media might be related to increased fluid clearance.

Role of actin in regulation of epithelial sodium channels by CFTR

1997 ◽  
Vol 272 (4) ◽  
pp. C1077-C1086 ◽  
Author(s):  
I. I. Ismailov ◽  
B. K. Berdiev ◽  
V. G. Shlyonsky ◽  
C. M. Fuller ◽  
A. G. Prat ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Actin Filaments ◽  
Single Channel ◽  
Na Channel ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Open Probability ◽  
Airway Epithelia ◽  
Alpha Beta ◽  
Actin Protein

Cystic fibrosis (CF) airway epithelia exhibit enhanced Na+ reabsorption in parallel with diminished Cl- secretion. We tested the hypothesis that actin plays a role in the regulation of a cloned epithelial Na+ channel (ENaC) by the cystic fibrosis transmembrane conductance regulator (CFTR). We found that immunopurified bovine tracheal CFTR coreconstituted into a planar lipid bilayer with alpha,beta,gamma-rat ENaC (rENaC) decreased single-channel open probability (Po) of rENaC in the presence of actin by over 60%, a significantly greater effect than was observed in the absence of actin (approximately 20%). In the presence of actin, protein kinase A plus ATP activated both CFTR and rENaC, but CFTR was activated in a sustained manner, whereas the activation of rENaC was transitory. ATP alone could also activate ENaC transiently in the presence ofactin but had no effect on CFTR. Stabilizing short actin filaments at a fixed length with gelsolin (at a ratio to actin of 2:1) produced a sustained activation of alpha,beta,gamma-rENaC in both the presence or absence of CFTR. Gelsolin alone (i.e., in the absence of actin) had no effect on the conductance or Po of either CFTR or rENaC. We have also found that short actin filaments produced their modulatory action on alpha-rENaC independent of the presence of the beta- or gamma-rENaC subunits. In contrast, CFTR did not affect any properties of the channel formed by alpha-rENaC alone, i.e., in the absence of beta- or gamma-rENaC. These results indicate that CFTR can directly downregulate single Na+ channel activity, which may account for the observed differences between Na+ transport in normal and CF-affected airway epithelia. Moreover, the presence of actin confers an enhanced modulatory ability of CFTR on Na+ channels.

Epithelial Na+channel inhibitors for the treatment of cystic fibrosis

2017 ◽  
Vol 6 (4) ◽  
pp. 181-190 ◽  
Author(s):  
Nichola J Smith ◽  
Catherine F Solovay
Keyword(s):  
Cystic Fibrosis ◽  
Na Channel ◽  
Epithelial Na Channel

Noncoordinated expression of alpha-, beta-, and gamma-subunit mRNAs of epithelial Na+ channel along rat respiratory tract

1997 ◽  
Vol 272 (1) ◽  
pp. C131-C141 ◽  
Author(s):  
N. Farman ◽  
C. R. Talbot ◽  
R. Boucher ◽  
M. Fay ◽  
C. Canessa ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Respiratory Tract ◽  
Mrna Level ◽  
Airway Epithelial Cells ◽  
Respiratory Physiology ◽  
Na Channel ◽  
Alveolar Cells ◽  
Cellular Expression ◽  
Alpha Beta ◽  
Epithelial Na Channel

Na+ reabsorption from the epithelial surface of the respiratory tract plays a fundamental role in respiratory physiology. As in the epithelia of the renal collecting tubule and distal colon, Na+ enters across the luminal surface of respiratory epithelial cells via a recently cloned amiloride-sensitive multisubunit (alpha, beta, gamma) epithelial Na+ channel. We have examined the cellular expression at the mRNA level of the alpha-, beta-, and gamma-subunits of rat epithelial Na+ channel (rENaC) in the rat lung and upper airway epithelial cells using in situ hybridization. A large prevalence of alpha- and gamma-rENaC subunit expression (over beta) was found in tracheal epithelium, in a subpopulation of alveolar cells, presumably type II pneumocytes, and in nasal and tracheal gland acini. In contrast, equivalent levels of expression of all three subunits were detected in bronchiolar epithelium and in rat nasal gland ducts. This diversity of expression may reflect cell-specific functions of the amiloride-sensitive Na+ channel along the respiratory tract.

In vivo analysis of fluid transport in cystic fibrosis airway epithelia of bronchial xenografts

1996 ◽  
Vol 270 (5) ◽  
pp. C1326-C1335 ◽  
Author(s):  
Y. Zhang ◽  
J. Yankaskas ◽  
J. Wilson ◽  
J. F. Engelhardt
Keyword(s):  
Cystic Fibrosis ◽  
Fluid Transport ◽  
Xenograft Model ◽  
Na Channel ◽  
Transmembrane Conductance Regulator ◽  
Fluid Absorption ◽  
Cystic Fibrosis Airway ◽  
In Vivo Analysis ◽  
Cf Transmembrane Conductance Regulator

An in vivo human bronchial xenograft model system was used to simultaneously analyze electrolyte and fluid transport defects in fully differentiated human cystic fibrosis (CF) and non-CF proximal airways. CF airways demonstrated three discernible defects when compared with non-CF, including 1) a lack of adenosine 3',5'-cylic monophosphate (cAMP)-inducible Cl- secretion, 2) a fourfold higher basal fluid absorption rate, and 3) an altered regulation of fluid absorption in response to amiloride-stimulated changes in Na+ transport. A unique finding in this study demonstrated that treatment of epithelia with amiloride led to a greater than threefold decrease in the rate of fluid absorption in CF tissues as contrasted to a greater than threefold increase in the rate of fluid absorption in non-CF tissues. The removal of apical Na+ from amiloride-treated non-CF xenografts was capable of ablating this amiloride-induced increase in fluid absorption. In light of the recent interactions demonstrated between CF transmembrane conductance regulator (CFTR) and the rat epithelial, amiloride-sensitive Na+ channel, these findings implicate additional complexities between the Na+ conductance pathways and fluid transport in normal and CF proximal airways. Such findings suggest that CFTR may also regulate amiloride-insensitive Na+ channels.

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