Adrenergic stimulation of Na+transport across alveolar epithelial cells involves activation of apical Cl−channels

1998 ◽  
Vol 275 (6) ◽  
pp. C1610-C1620 ◽  
Author(s):  
Xinpo Jiang ◽  
David H. Ingbar ◽  
Scott M. O’Grady
Keyword(s):  
Epithelial Cells ◽  
Short Circuit ◽  
Methanesulfonic Acid ◽  
Reversal Potential ◽  
Short Circuit Current ◽  
Alveolar Epithelial Cells ◽  
Sprague Dawley ◽  
Adrenergic Stimulation ◽  
Alveolar Epithelial ◽  
Stimulation Of

Alveolar epithelial cells were isolated from adult Sprague-Dawley rats and grown to confluence on membrane filters. Most of the basal short-circuit current ( I sc; 60%) was inhibited by amiloride (IC50 0.96 μM) or benzamil (IC50 0.5 μM). Basolateral addition of terbutaline (2 μM) produced a rapid decrease in I sc, followed by a slow recovery back to its initial amplitude. When Cl− was replaced with methanesulfonic acid, the basal I sc was reduced and the response to terbutaline was inhibited. In permeabilized monolayer experiments, both terbutaline and amiloride produced sustained decreases in current. The current-voltage relationship of the terbutaline-sensitive current had a reversal potential of −28 mV. Increasing Cl− concentration in the basolateral solution shifted the reversal potential to more depolarized voltages. These results were consistent with the existence of a terbutaline-activated Cl− conductance in the apical membrane. Terbutaline did not increase the amiloride-sensitive Na+ conductance. We conclude that β-adrenergic stimulation of adult alveolar epithelial cells results in an increase in apical Cl− permeability and that amiloride-sensitive Na+ channels are not directly affected by this stimulation.

Selectivity properties of a Na-dependent amino acid cotransport system in adult alveolar epithelial cells

2000 ◽  
Vol 279 (5) ◽  
pp. L911-L915 ◽  
Author(s):  
Xinpo Jiang ◽  
David H. Ingbar ◽  
Scott M. O'Grady
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Epithelial Cells ◽  
Short Circuit ◽  
Critical Role ◽  
Short Circuit Current ◽  
Alveolar Epithelial Cells ◽  
Alveolar Epithelial ◽  
Adult Rat ◽  
Cotransport System

We investigated the amino acid specificity of a Na-dependent amino acid cotransport system that contributes to transepithelial Na absorption in the apical membrane of cultured adult rat alveolar epithelial cell monolayers. Short-circuit current was increased by basic, uncharged polar, and nonpolar amino acids but not by l-aspartic acid or l-proline. EC50 values for l-lysine andl-histidine were 0.16 and 0.058 mM, respectively. Thel-lysine-stimulated short-circuit current was Na dependent, with a concentration causing a half-maximal stimulation by Na of 44.24 mM. l-Serine, l-glutamine, andl-cysteine had EC50 values of 0.095, 0.25, and 0.12 mM, respectively. l-Alanine had the highest affinity, with an EC50 of 0.027 mM. We conclude that monolayer cultures of adult rat alveolar epithelial cells possess a broad-specificity Na-dependent amino acid cotransport system with properties consistent with system B0,+. We suggest that this cotransport system plays a critical role in recycling of constituent amino acids that make up glutathione, thus ensuring efficient replenishment of this important antioxidant within the alveolar fluid.

Cl-channel activation is necessary for stimulation of Na transport in adult alveolar epithelial cells

2000 ◽  
Vol 278 (2) ◽  
pp. L239-L244 ◽  
Author(s):  
Scott M. O'Grady ◽  
Xinpo Jiang ◽  
David H. Ingbar
Keyword(s):  
Epithelial Cells ◽  
Adrenergic Receptor ◽  
Apical Membrane ◽  
Receptor Activation ◽  
Alveolar Epithelial Cells ◽  
Na Channels ◽  
Channel Activation ◽  
Alveolar Epithelial ◽  
Cl Channel ◽  
Stimulation Of

In this review, we discuss evidence that supports the hypothesis that adrenergic stimulation of transepithelial Na absorption across the alveolar epithelium occurs indirectly by activation of apical Cl channels, resulting in hyperpolarization and an increased driving force for Na uptake through amiloride-sensitive Na channels. This hypothesis differs from the prevailing idea that adrenergic-receptor activation increases the open probability of Na channels, leading to an increase in apical membrane Na permeability and an increase in Na and fluid uptake from the alveolar space. We review results from cultured alveolar epithelial cell monolayer experiments that show increases in apical membrane Cl conductance in the absence of any change in Na conductance after stimulation by selective β-adrenergic-receptor agonists. We also discuss possible reasons for differences in Na-channel regulation in cells grown in monolayer culture compared with that in dissociated alveolar epithelial cells. Finally, we describe some preliminary in vivo data that suggest a role for Cl-channel activation in the process of amiloride-sensitive alveolar fluid absorption.

scholarly journals Mechanisms of EGF-induced stimulation of sodium reabsorption by alveolar epithelial cells

1998 ◽  
Vol 275 (1) ◽  
pp. C82-C92 ◽  
Author(s):  
Spencer I. Danto ◽  
Zea Borok ◽  
Xiao-Ling Zhang ◽  
Melissa Z. Lopez ◽  
Paryus Patel ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Alveolar Epithelium ◽  
Alveolar Epithelial Cells ◽  
Cell Labeling ◽  
Northern Analysis ◽  
Sodium Reabsorption ◽  
Alveolar Epithelial ◽  
Subunit Mrna ◽  
Epidermal Growth ◽  
Stimulation Of

We investigated the effects of epidermal growth factor (EGF) on active Na+ absorption by alveolar epithelium. Rat alveolar epithelial cells (AEC) were isolated and cultivated in serum-free medium on tissue culture-treated polycarbonate filters. mRNA for rat epithelial Na+ channel (rENaC) α-, β-, and γ-subunits and Na+ pump α1- and β1-subunits were detected in day 4 monolayers by Northern analysis and were unchanged in abundance in day 5 monolayers in the absence of EGF. Monolayers cultivated in the presence of EGF (20 ng/ml) for 24 h from day 4 to day 5 showed an increase in both α1 and β1Na+ pump subunit mRNA but no increase in rENaC subunit mRNA. EGF-treated monolayers showed parallel increases in Na+ pump α1- and β1-subunit protein by immunoblot relative to untreated monolayers. Fixed AEC monolayers demonstrated predominantly membrane-associated immunofluorescent labeling with anti-Na+ pump α1- and β1-subunit antibodies, with increased intensity of cell labeling for both subunits seen at 24 h following exposure to EGF. These changes in Na+ pump mRNA and protein preceded a delayed (>12 h) increase in short-current circuit (measure of active transepithelial Na+transport) across monolayers treated with EGF compared with untreated monolayers. We conclude that EGF increases active Na+ resorption across AEC monolayers primarily via direct effects on Na+ pump subunit mRNA expression and protein synthesis, leading to increased numbers of functional Na+ pumps in the basolateral membranes.

Hormonal regulation of Na+-K+-ATPase in cultured epithelial cells

1986 ◽  
Vol 251 (2) ◽  
pp. C186-C190 ◽  
Author(s):  
J. P. Johnson ◽  
D. Jones ◽  
W. P. Wiesmann
Keyword(s):  
Enzyme Activity ◽  
Epithelial Cells ◽  
Atpase Activity ◽  
Hormonal Regulation ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Toad Urinary Bladder ◽  
A6 Cells ◽  
Cultured Epithelial Cells ◽  
Stimulation Of

Aldosterone and insulin stimulate Na+ transport through mechanisms involving protein synthesis. Na+-K+-ATPase has been implicated in the action of both hormones. We examined the effect of aldosterone and insulin on Na+-K+-ATPase in epithelial cells in culture derived from toad urinary bladder (TB6C) and toad kidney (A6). Aldosterone, but not insulin, increases short-circuit current (ISC) in TB6C cells. Aldosterone increases Na+-K+-ATPase activity after 18 h of incubation, but no effect can be seen at 3 and 6 h. Amiloride, which inhibits aldosterone-induced increases in ISC, has no effect on either basal or aldosterone stimulated enzyme activity. Both aldosterone and insulin increase ISC in A6 cells and when added together are synergistic. Aldosterone stimulates enzyme activity in A6 cells, but insulin alone has no effect. However, aldosterone and insulin together stimulate enzyme activity more than aldosterone alone. It appears that stimulation of Na+-K+-ATPase activity is involved in aldosterone action in both cell lines but does not appear to be due to increased Na+ entry, since enhanced enzyme activity is not inhibited by amiloride. In contrast, insulin alone has no direct effect on Na+-K+-ATPase, although the increased enzyme activity following both agents in combination may explain their synergism on ISC.

Evidence for separate cellular origins of sodium and acid-base transport in the turtle bladder

1986 ◽  
Vol 250 (4) ◽  
pp. C609-C616 ◽  
Author(s):  
J. H. Durham ◽  
W. Nagel
Keyword(s):  
Epithelial Cells ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Transport Processes ◽  
Electrical Parameters ◽  
Acid Base ◽  
Intracellular Potential ◽  
Turtle Bladder ◽  
Stimulation Of

Transmembrane electrical parameters of the epithelial cells in short-circuited turtle bladders were measured to determine whether those cells participating in Na reabsorption also participate in electrogenic transepithelial acidification and alkalinization. Amiloride-induced increases in intracellular potential (Vsca), apical fractional resistance (FRa), and concomitant decreases in short-circuit current (Isc) denote the participation of the impaled cells in Na reabsorption. In bladders from postabsorptive turtles, amiloride increased Vsca by -45 mV, increased FRa by 37%, and decreased Isc from 36 to -10 microA/cm2. In bladders from NaHCO3-loaded turtles, amiloride increased Vsca by -21 mV, FRa by 21%, and decreased Isc from 22 to 0 microA/cm2. Neither the subsequent inhibition of the negative acidification current in postabsorptive bladders, nor stimulation of positive alkalinization current in bladders from NaHCO3-loaded turtles was associated with any transmembrane electrical change that could be attributed to changes in those transport processes. It is concluded that the electrogenic luminal acidification and alkalinization processes of the turtle bladder are not produced by, or electrically coupled to, those cells that are involved in Na reabsorption.

Tight monolayers of rat alveolar epithelial cells: bioelectric properties and active sodium transport

1989 ◽  
Vol 256 (3) ◽  
pp. C688-C693 ◽  
Author(s):  
J. M. Cheek ◽  
K. J. Kim ◽  
E. D. Crandall
Keyword(s):  
Epithelial Cells ◽  
Sodium Transport ◽  
Short Circuit ◽  
Alveolar Epithelium ◽  
Alveolar Epithelial Cells ◽  
Active Sodium ◽  
Alveolar Epithelial ◽  
Active Sodium Transport ◽  
Complex Anatomy

Because the pulmonary alveolar epithelium separates air spaces from a fluid-filled compartment, it is expected that this barrier would be highly resistant to the flow of solutes and water. Investigation of alveolar epithelial resistance has been limited due to the complex anatomy of adult mammalian lung. Previous efforts to study isolated alveolar epithelium cultured on porous substrata yielded leaky monolayers. In this study, alveolar epithelial cells isolated from rat lungs and grown on tissue culture-treated Nucleopore filters resulted in tight monolayers with transepithelial resistance greater than 2,000 omega.cm2. Changes in bioelectric properties of these alveolar epithelial monolayers in response to ouabain, amiloride, and terbutaline are consistent with active sodium transport across a polarized barrier. 22Na flux measurements under short-circuit conditions directly confirm net transepithelial absorption of sodium by alveolar epithelial cells in the apical to basolateral direction, comparable to the observed short-circuit current (4.37 microA/cm2). The transport properties of these tight monolayers may be representative of the characteristics of the mammalian alveolar epithelial barrier in vivo.

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