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.

Variations in epithelial Na+ transport and epithelial sodium channel localisation in the vaginal cul-de-sac of the brushtail possum, Trichosurus vulpecula, during the oestrous cycle

2016 ◽  
Vol 28 (3) ◽  
pp. 328
Author(s):  
T.-A. Alsop ◽  
B. J. McLeod ◽  
A. G. Butt
Keyword(s):  
Epithelial Cells ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Na Channel ◽  
Brushtail Possum ◽  
Trichosurus Vulpecula ◽  
Fluid Absorption ◽  
Na Transport ◽  
Polymerase Chain ◽  
Epithelial Na Channel

The fluid in the vaginal cul-de-sac of the brushtail possum, Trichosurus vulpecula, is copious at ovulation when it may be involved in sperm transport or maturation, but is rapidly reabsorbed following ovulation. We have used the Ussing short-circuit current (Isc) technique and measurements of transcript and protein expression of the epithelial Na+ channel (ENaC) to determine if variations in electrogenic Na+ transport are associated with this fluid absorption. Spontaneous Isc (<20 µA cm–2 during anoestrus, 60–80 µA cm–2 in cycling animals) was inhibited by serosal ouabain. Mucosal amiloride (10 µmol L–1), an inhibitor of ENaC, had little effect on follicular Isc but reduced luteal Isc by ~35%. This amiloride-sensitive Isc was dependent on mucosal Na+ and the half-maximal inhibitory concentration (IC50)–amiloride (0.95 μmol L–1) was consistent with ENaC-mediated Na+ absorption. Results from polymerase chain reaction with reverse transcription (RT-PCR) indicate that αENaC mRNA is expressed in anoestrous, follicular and luteal phases. However, in follicular animals αENaC immunoreactivity in epithelial cells was distributed throughout the cytoplasm, whereas immunoreactivity was restricted to the apical pole of cells from luteal animals. These data suggest that increased Na+ absorption contributes to fluid absorption during the luteal phase and is regulated by insertion of ENaC into the apical membrane of cul-de-sac epithelial cells.

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.

Modification of carboxyl of Na+ channel inhibits aldosterone action on Na+ transport

1983 ◽  
Vol 245 (6) ◽  
pp. F726-F734 ◽  
Author(s):  
J. Kipnowski ◽  
C. S. Park ◽  
D. D. Fanestil
Keyword(s):  
Amphotericin B ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Na Channel ◽  
Dependent Manner ◽  
Na Channels ◽  
Na Transport ◽  
Maximal Increase ◽  
Osmotic Water ◽  
Stimulation Of

We investigated the effect of the carboxyl-selective reagent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) on aldosterone stimulation of Na+ transport in the urinary bladder of the toad. Na+ transport, measured as the short-circuit current (SCC), was irreversibly inhibited by EEDQ in a dose- and time-dependent manner prior to addition of aldosterone. The greater the percentage inhibition by EEDQ (X), the smaller was the maximal increase of SCC after aldosterone (Y). This relationship gave the regression equation Y = 128.41 - 1.73X, r = -0.99 (n = 35). Evidence that the inhibition of SCC produced by EEDQ was limited to effects at the mucosal membrane was attested by the following: 1) EEDQ did not alter the stimulation by aldosterone of the osmotic water flow response to antidiuretic hormone; 2) whereas inhibition of protein synthesis by cycloheximide prevented this effect of aldosterone; 3) amphotericin B fully restored SCC previously inhibited by EEDQ to the level produced in tissues not inhibited by EEDQ; 4) comparison of the effects of amiloride vs. EEDQ pretreatment on the SCC response to aldosterone and amphotericin B revealed nearly identical characteristics; 5) in contrast, amphotericin B stimulation of SCC was limited when Na+ transport was limited by antimycin A (an inhibitor of energy production) or by ouabain. The findings fail to provide positive evidence for the hypothesis that aldosterone induces the synthesis of new Na+ channels but are consistent with hormonal activation of previously existing but nonfunctioning Na+ channels.

Regulation of electrogenic Na+ transport across leech skin

1995 ◽  
Vol 268 (3) ◽  
pp. R605-R613 ◽  
Author(s):  
W. M. Weber ◽  
U. Blank ◽  
W. Clauss
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Na Channel ◽  
Monovalent Cations ◽  
Serosal Side ◽  
Na Transport ◽  
Permeability Ratio ◽  
Cyclic Monophosphate ◽  
Apical Side ◽  
Stimulation Of

The dorsal integument of the medical leech Hirudo medicinalis exhibits a marked amiloride-sensitive Na+ absorption. With 20 mM Na+ in the apical solution, the transepithelial short-circuit current (Isc) was approximately 40% higher than with 115 mM Na+, whereas the transepithelial potential (VT) with 20 mM Na+ was -35.7 +/- 4.5 and -20.6 +/- 2.6 mV with 115 mM Na+. Amiloride (100 microM) inhibition at 20 mM apical Na+ was also significantly larger than with 115 mM Na+ in the solution. Benzamil (100 microM) showed additional inhibition after amiloride. Large transient overshooting currents occurred only when 115 mM Na+ was added after some minutes of Na(+)-free apical solution. Addition of adenosine 3',5'-cyclic monophosphate (cAMP) to the serosal side in the presence of 115 mM apical Na+ nearly doubled Isc. This cAMP effect was reduced to only 20% in the presence of 20 mM Na+. Guanosine 3',5'-cyclic monophosphate (cGMP) slightly increased Isc, whereas ATP showed biphasic potency. Removal of calcium from the apical side resulted in a large stimulation of amiloride-sensitive Isc only in the presence of 115 mM Na+. When currents were activated with cAMP, a deprivation of Ca2+ modestly reduced the amiloride-sensitive Isc. The Na+ channel of leech integument was found highly selective for Na+ over other monovalent cations. The permeability ratio for Na+ over K+ was approximately 30:1; the selectivity relationship for the investigated cations was Na+ > Li+ > NH4+ > K+ approximately Cs+ approximately Rb+.

Increased Po2 alters the bioelectric properties of fetal distal lung epithelium

1996 ◽  
Vol 270 (6) ◽  
pp. L1060-L1066 ◽  
Author(s):  
O. Pitkanen ◽  
A. K. Transwell ◽  
G. Downey ◽  
H. O'Brodovich
Keyword(s):  
Short Circuit ◽  
Primary Cultures ◽  
Short Circuit Current ◽  
Na Channel ◽  
Lung Epithelium ◽  
Ambient Oxygen ◽  
Ion Substitution ◽  
Distal Lung ◽  
Dose Dependent ◽  
Oxygen Concentrations

At birth the lung must efficiently clear the liquid from its air spaces and permanently convert from a fluid-secreting to a fluid-absorbing organ. When primary cultures of rat fetal distal lung epithelium (FDLE) grown on permeable supports were switched from a fetal (3%) to a postnatal (21%) oxygen environment, there was an increase in epithelial permeability as reflected by a dose-dependent decline in transepithelial resistance (Rt) 4 h later (3% = 239 +/- 19 omega.cm2; 21% = 170 +/- 28 omega.cm2; 50% = 98 +/- 20 omega.cm2; P < 0.05). The effect was transient, since monolayers initially maintained at 3% and switched to these higher oxygen concentrations subsequently had Rt values comparable to the 3% group at 48 h (3% = 153 +/- 17 omega.cm2; 21% = 181 +/- 19 omega.cm2; 50% = 192 +/- 21 omega.cm2; P = NS). Changes in Rt were associated with expected changes in the histological appearance of the interepithelial tight junctions, but intracellular actin content and distribution remained constant. Amiloride-sensitive equivalent short-circuit current increased within 18 h, with further increases after 48 h of exposure to postnatal oxygen concentrations. Ion substitution experiments suggested diminished FDLE Cl transport and increased Na transport. The amount of FDLE-alpha, -beta, and -gamma rat epithelial Na channel mRNA increased within 48 h of increasing the ambient oxygen concentration. These results suggest that the physiological increase in alveolar Po2 at birth is, at least in part, responsible for distal lung's permanent switch from Cl secretion to Na absorption at birth.

Regulation of the epithelial Na+ channel by extracellular acidification

2000 ◽  
Vol 279 (6) ◽  
pp. C1896-C1905 ◽  
Author(s):  
Mouhamed S. Awayda ◽  
Michael J. Boudreaux ◽  
Roxanne L. Reger ◽  
L. Lee Hamm
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Na Channel ◽  
Fluctuation Analysis ◽  
Extracellular Acidification ◽  
A6 Epithelia ◽  
Electrode Voltage ◽  
Effects Of Ph ◽  
Intracellular Ca ◽  
Epithelial Na Channel

The effect of extracellular acidification was tested on the native epithelial Na+ channel (ENaC) in A6 epithelia and on the cloned ENaC expressed in Xenopusoocytes. Channel activity was determined utilizing blocker-induced fluctuation analysis in A6 epithelia and dual electrode voltage clamp in oocytes. In A6 cells, a decrease of extracellular pH (pHo) from 7.4 to 6.4 caused a slow stimulation of the amiloride-sensitive short-circuit current ( I Na) by 68.4 ± 11% ( n = 9) at 60 min. This increase of I Na was attributed to an increase of open channel and total channel ( N T) densities. Similar changes were observed with pHo 5.4. The effects of pHo were blocked by buffering intracellular Ca2+ with 5 μM 1,2-bis(2-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid. In oocytes, pHo 6.4 elicited a small transient increase of the slope conductance of the cloned ENaC (11.4 ± 2.2% at 2 min) followed by a decrease to 83.7 ± 11.7% of control at 60 min ( n = 6). Thus small decreases of pHostimulate the native ENaC by increasing N T but do not appreciably affect ENaC expressed in Xenopus oocytes. These effects are distinct from those observed with decreasing intracellular pH with permeant buffers that are known to inhibit ENaC.

Inhibition of N-glycosylation affects transepithelial Na+ but not Na+-K+-ATPase transport

1989 ◽  
Vol 256 (5) ◽  
pp. C958-C966 ◽  
Author(s):  
D. Zamofing ◽  
B. C. Rossier ◽  
K. Geering
Keyword(s):  
Cell Surface ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Beta Subunit ◽  
Beta Subunits ◽  
Toad Urinary Bladder ◽  
Na Transport ◽  
Atpase Inhibition ◽  
Dose Dependent

Tunicamycin (TM) was used in toad urinary bladder (TBM) cells to study the role of N-glycosylation of the beta-subunit of Na+-K+-ATPase. Inhibition of the beta-subunit core glycosylation was dose dependent and coincided with a specific 70% decrease in newly synthesized beta- and alpha-subunits. Na+-K+-ATPase activity paralleled the decrease in the cellular content of the alpha-subunit, although the cellular and cell surface-expressed Na+-K+-ATPase pool was progressively filled up with nonglycosylated beta-subunits. In addition, the decrease in maximal Na+ transport capacity of the Na+-K+-ATPase as assessed by short-circuit current (SCC) measurements in the presence of amphotericin B correlated with the decrease in the total cell surface-expressed beta-subunit population despite the fact that it was composed of 47% nonglycosylated beta-subunits after 42 h of TM treatment. These results are consistent with the interpretation that beta-subunit glycosylation is not important either for the enzyme's intracellular sorting to the plasma membrane or its hydrolytic and transport properties. Finally, TM produced effects on basal SCC and electrical resistance that differed in their times of onset and time periods needed for recovery. Thus, in addition to the Na+-K+-ATPase, other glycoproteins in the apical membrane and the tight junctions must be implicated in the maintenance of transepithelial Na+ transport.

Role of carboxyl group in Na+-entry step at apical membrane of toad urinary bladder

1983 ◽  
Vol 245 (6) ◽  
pp. F707-F715 ◽  
Author(s):  
C. S. Park ◽  
J. Kipnowski ◽  
D. D. Fanestil
Keyword(s):  
Urinary Bladder ◽  
Apical Membrane ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Complete Recovery ◽  
Na Channel ◽  
Toad Urinary Bladder ◽  
Carboxyl Group ◽  
Na Transport ◽  
Tight Epithelia

Mucosal addition of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) and some lipid-soluble carbodiimides, agents which are selective for carboxyl groups, irreversibly inhibited Na+ transport as measured by short-circuit current (SCC) in the urinary bladder of the toad. The inhibition of Na+ transport by EEDQ had the following characteristics: 1) the inhibition was accompanied by a significant increase in the transepithelial electrical resistance; 2) the decrease in SCC was accounted for by a comparable decrease in 22Na+ influx without effect on Na+ efflux; 3) amphotericin B produced complete recovery of SCC inhibited with EEDQ but not with antimycin A or ouabain; 4) mucosal EEDQ decreased the amiloride-sensitive reversal of Na+ current that is induced by serosal nystatin in the absence of mucosal Na+; 5) vasopressin and acid mucosal pH caused an increase in SCC in proportion to the SCC remaining after EEDQ inhibition; and 6) Vmax of the SCC was decreased without alteration in the apparent Km for Na+. Based on these characteristics of EEDQ inhibition of Na+ transport, we infer that a carboxyl group of the Na+ channel is involved in the Na+-entry step across the apical membrane of “tight” epithelia. The inhibition of Na+ transport with EEDQ most likely involves closing the Na+ channel through a chemical reaction involving a carboxyl group of the channel.

The toxicity of exposure to the organochlorine, dieldrin, at a sympathetic junction and on the skin of the frog,Caudiverbera caudiverbera

2002 ◽  
Vol 21 (11) ◽  
pp. 587-591 ◽  
Author(s):  
M Suwalsky ◽  
B Norris ◽  
M Benites
Keyword(s):  
Protein Complexes ◽  
Slow Component ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Initial Increase ◽  
Na Channel ◽  
Electrical Parameters ◽  
Progressive Reduction ◽  
Channel Inactivation ◽  
Epithelial Na Channel

The effects of the organochlorine, dieldrin, were tested on a noradrenergic synapse of the frog, Caudiverbera caudiverbera. Nerve stimulation induced a transient increase in short circuit current (SCC) and in the potential difference (PD), which consisted of a rapid and then a slow component. Dieldrin in the concentration range 0.01–1.0 mM caused a concentration-dependent block of both components to 32% of their control values, which was partially reversed by washout. In some experiments, this blocking effect was preceded by an initial increase in the magnitude of the electrical parameters of the nonstimulated skin and also in the synaptic response to stimulation when the lowest dieldrin concentration (0.01 mM) was applied; higher concentrations (0.1–1.0 mM) led to progressive reduction of the responses. Results are interpreted as a perturbation of the lipid bilayer structure, which affects the functionality of lipid–protein complexes, leading, on one hand, to glandular Cl¡ channel inactivation and epithelial Na + channel blockade and, on the other hand, to transient glandular Cl¡ activation, opening of a putative Na+channel, and subsequent blockade.

Aldosterone modulates electrogenic Cl secretion in the colon of the hen (Gallus domesticus)

1991 ◽  
Vol 261 (6) ◽  
pp. R1533-R1541 ◽  
Author(s):  
W. Clauss ◽  
V. Dantzer ◽  
E. Skadhauge
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Na Channel ◽  
Na Transport ◽  
Electrogenic Transport ◽  
Ussing Chambers ◽  
Cl Secretion ◽  
Cotransport System ◽  
Hormonal Stimulus

The regulation of Na and Cl transport in hen colon by mineralocorticoids was investigated with isolated epithelia in vitro by histological and electrophysiological techniques. The electrogenic transport of Na and Cl was measured in Ussing chambers by the short-circuit current technique and was identified by the specific inhibitors amiloride and bumetanide or by the secretagogue theophylline. Hens were maintained either on low (LS)- or on high-NaCl diets (HS), and the plasma aldosterone (PA) levels of these groups were measured with radioimmunoassay. A group of HS hens received injections of aldosterone at a 6-h schedule before experiments. A group of LS hens was resalinated, and experiments were carried out at a 24-h interval for up to 3 days after resalination. The LS diet stimulated PA levels ninefold, compared with HS hens. Na transport was modulated by the hormonal stimulus in a way that the apical Na entry switched from an electrogenic Na-amino acid-hexose cotransport system completely to an amiloride-sensitive Na channel. Electrogenic Cl secretion was induced by theophylline and was inhibited by bumetanide. NaCl deprivation, resalination or aldosterone injection modulated electrogenic Cl secretion in parallel between 7 (HS) and 14.4 mu eq.cm-2.h-1 (LS), with pronounced alteration in tissue conductance. These findings reveal a new action of aldosterone that, besides stimulating Na absorption, also directly or indirectly modulates Cl secretion.

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