search text   Advanced Search

This Article Abstract Full Text (PDF) P3Rs: Submit a response Alert me when this article is cited Alert me when P3Rs are posted Alert me if a correction is posted Citation Map Services E-mail this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Add to My File Cabinet Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via ISI Web of Science (15) Citing Articles via Google Scholar Google Scholar Articles by Helve, O. Articles by Otulakowski, G. Search for Related Content PubMed PubMed Citation Articles by Helve, O. Articles by Otulakowski, G. Related Collections Premature & Newborn

Low Expression of Human Epithelial Sodium Channel in Airway Epithelium of Preterm Infants With Respiratory Distress

Otto Helve, MD^*, Olli M. Pitkänen, MD, PhD, Sture Andersson, MD, PhD^*, Hugh O’Brodovich, MD^,||, Turkka Kirjavainen, MD, PhD^* and Gail Otulakowski, PhD^||

^* Departments of Neonatology
Cardiology, Hospital for Children and Adolescents, Helsinki University Central Hospital, Helsinki, Finland
Departments of Paediatrics and Physiology, University of Toronto, Toronto, Ontario, Canada
^|| Programme in Lung Biology Research, Research Institute of the Hospital for Sick Children, Toronto, Ontario, Canada

	ABSTRACT

TOP ABSTRACT METHODS RESULTS DISCUSSION REFERENCES

 
Objective. Active ion transport is critical to postnatal clearance of lung fluid. The importance of epithelial sodium channel (ENaC) in this clearance has been demonstrated in animal studies in which -ENaC knockout mice died postnatally as a result of respiratory insufficiency. In animals, the expression of -ENaC in respiratory epithelium is dependent on gestational age, but when assessed by in situ hybridization in the human (h), the mRNA is present from the earliest stages of pulmonary development. Therefore, the purpose of the present investigation was to quantify mRNA of the -, ß-, and -hENaC subunits of newborn preterm infants with respiratory distress and compare the gene expression data against those detected in healthy term infants. In addition, the effect of systemic dexamethasone therapy on the 3 hENaC subunits was studied in 4 preterm infants who received prolonged assisted ventilation.

Methods. The expression of subunits of hENaC was determined in samples taken from nasal respiratory epithelium of 7 healthy term infants (gestation age: 39.3 ± 0.9 weeks [mean ± standard deviation) and 5 preterm infants (gestational age: 27.2 ± 0.9 weeks) with respiratory distress syndrome within 5 hours of birth. Betamethasone had been given to all mothers of preterm infants. In 4 additional preterm infants who still required assisted ventilation at 43 ± 6 days postnatal age, the expression of -hENaC was determined in samples taken before and during treatment with dexamethasone.

Results. Preterm infants with respiratory distress syndrome had low expression of all hENaC subunits relative to healthy term infants (-hENaC: 5.38 ± 2.01 [amol/fmol cytokeratin 18] vs 9.13 ± 2.26; ß-hENaC: 2.44 ± 1.43 vs 4.25 ± 1.10; -hENaC: 2.43 ± 0.11 vs 6.81 ± 3.24). Each of the 4 preterm infants who were treated with dexamethasone at 1 month of age showed an increase in expression of -hENaC and ß-hENaC subunit normalized to cytokeratin 18.

Conclusion. All 3 subunits of the hENaC are low in preterm relative to full-term infants. -hENaC mRNA in respiratory epithelium is increased by therapeutic doses of glucocorticosteroid. Low expression of -hENaC in human respiratory epithelium may play a role in the pathogenesis of respiratory distress in preterm infants.

Key Words: epithelium • glucocorticoid • ion transport • lung liquid • respiratory distress syndrome

Abbreviations: ENaC, epithelial sodium channel • PD, potential difference • RDS, respiratory distress syndrome • hENaC, human epithelial sodium channel • QRT-PCR, quantitative reverse transcriptase–polymerase chain reaction • CK, cytokeratin

Active ion transport plays a critical role in the liquid movement across the fetal and perinatal lung epithelium.^1–3 The fetal lung actively secretes Cl^– and fluid throughout gestation and develops the ability to actively reabsorb Na⁺ only during late gestation.⁴ At birth, the mature lung switches from active Cl^– and fluid secretion to active Na⁺ and fluid absorption in response to circulating catecholamines and changes in oxygen tension.^2,5–7 The active absorption of fluid is coupled with vectorial Na⁺ transport from the apical to the basolateral side of the epithelium. Inability to switch from secretion of fluid to absorption may contribute to the respiratory distress of the preterm infant.^2,3,8

The amiloride-sensitive epithelial sodium channel (ENaC) is important for transepithelial lung liquid movement. The channel consists of 3 subunits, of which the -subunit is prerequisite for appreciable channel function.⁹ Experiments in several animal models indicate that the function of ENaC is vital for lung fluid clearance at birth. Instillation of amiloride, a Na⁺ channel blocker, into the trachea of newborn guinea pigs results in impediment of lung liquid absorption, hypoxia, and respiratory distress.¹⁰ Loss-of-function mutations of the murine -ENaC gene results in early death of the newborn animals as a result of respiratory distress. Microscopy of the lungs of these homozygous knock-out test animals reveals normal morphologic development; however, gravimetric measurements showed excess lung fluid, and electrophysiologic measurements of the trachea showed impaired response to amiloride, suggesting reduced Na⁺ channel activity.¹¹ In humans, studies in premature infants have shown that the amiloride-sensitive drop in electrical potential difference (PD) between the nasal epithelium and the subcutaneous space, a surrogate measure for Na⁺ transport and ENaC activity, is decreased in infants who develop neonatal respiratory distress (RDS).⁸

Administration of corticosteroids for the treatment of neonatal RDS is an established intervention to reduce inflammation and promote lung maturity and surfactant production. Corticosteroids have been shown to increase lung -ENaC expression and function in fetal rat lung; however, data on the effects of glucocorticoid on human ENaC (hENaC) expression in humans in vivo have not previously been reported in the literature. In cultures of human fetal lung explants, a high dose of dexamethasone induced not only the -subunit but all 3 hENaC-subunit mRNAs by 2- to 3-fold.¹² Dexamethasone treatment induced -hENaC¹³ and -hENaC¹⁴ mRNAs of human lung–derived epithelial H441 cells (results for ß-hENaC have not been reported in the literature), but in the A549 cell line, dexamethasone induced significant increases in ß- and -hENaC mRNA and protein, with no significant effect on -hENaC.¹⁵ These studies indicate that lung explants and human cell lines maintained under different culture conditions generate a variety of hENaC-related responses to glucocorticoid treatment, any or all of which may not accurately mimic the response of the intact individual, and emphasize the need to complete in vivo experiments to determine the effects of glucocorticoid treatment on hENaC expression in human respiratory epithelium.

The expression of hENaC mRNA along the respiratory tract of adult humans has recently been described using both in situ hybridization and quantitative reverse transcriptase–polymerase chain reaction (QRT-PCR).¹⁶ However, no quantitative data exist on hENaC expression in respiratory epithelium of term and preterm infants. The nasal epithelium has been used as a representative of pulmonary epithelium because it displays electrophysiologic characteristics comparable to the more distal airway epithelium.^17–19

The aim of the present work was to study whether the epithelial expression of -, ß-, and -hENaC mRNA immediately after birth is different in preterm infants with RDS when compared with term infants without lung disease. In addition, we studied whether dexamethasone therapy had an effect on the hENaC subunits’ mRNA expression in 4 continuously ventilator-dependent preterm infants at 35 to 50 days of age.

	METHODS

TOP ABSTRACT METHODS RESULTS DISCUSSION REFERENCES

 
Patients
Patient data are given in Tables 1 and 2. Newborn infants were studied within 5 hours of birth. All 7 control term infants were healthy, whereas the 5 preterm infants had RDS; none of them received surfactant before sampling. The mothers had received ante partum betamethasone treatment as a total of 1 to 4 doses of 12 mg intramuscularly (from 18 days to 24 hours before delivery). Two mothers had received ante partum terbutaline: 1 received an infusion of 1 mg/hour for 6 hours, which was discontinued 5 hours before delivery; the second received 5 mg/hour for 48 hours until delivery. None of the mothers had preeclampsia, and none had diabetes or any other chronic conditions that would impose additional risks to pregnancy. The initial arterial to alveolar oxygen tension ratio of the 5 preterm infants was 0.05 to 0.8, and they received an average of 2 doses of surfactant (Curosurf; Chiesi, Parma, Italy). Four additional preterm infants with prolonged respiratory distress were studied. Treatment was started at 43 ± 6 postnatal days (gestational age: 24.9 ± 0.2 weeks; gestational weight: 764 ± 178 g). The infants received dexamethasone treatment at a dose of 0.2 mg/kg/day as 2 daily doses for 3 days and thereafter at 0.1 and 0.05 mg/kg/day for 3 and 5 days, respectively. All 4 infants were weaned successfully from the ventilator. Initial samples were gathered before the commencement of dexamethasone treatment. Subsequently, samples were gathered in these patients 7 to 20 hours after the initial dose.

Sample Collection and Storage
The samples were prepared and quantified as described previously.^16,20 The nasal samples were gathered under direct vision by scraping the nasal epithelium using a Rhino-Probe (Arlington Scientific, Springville, UT). In the patients who were treated with dexamethasone, the samples were gathered from the nare contralateral to the nare with the nasotracheal intubation tube. A commercially available purification kit was used for total RNA preparation (RNeasy Kit; Qiagen, Valencia, CA). The samples were collected on ice and immediately dispersed with insulin syringe into the lysis buffer containing 10 µ;L of ß-mercaptoethanol per 1 mL of buffer. The samples were stored at –80°C, and the succeeding purification steps were performed as sets of 5 to 8 samples as described by the manufacturer. The purified total RNA preparations were quantified by slot blot analysis, diluted to 2.4 ng/µ;L, and stored at –80°C in single-use aliquots as described previously.²⁰

In the preterm infants who received dexamethasone treatment, the total RNA quantification of the turbinate specimens was performed using a commercially available kit including preweighed standard RNA preparation and RiboGreen quantification reagent (RiboGreen RNA Quantitation Kit; Molecular Probes, Eugene, OR). The emission at 520 nm of the adducts was measured after excitation at 480 nm using a spectrofluorometer (LS50B; Perkin Elmer, Shelton, CT), and the sample RNA contents were deduced from the standard plot.

Quantification of mRNA
Samples for competitive QRT-PCR were thawed on ice and diluted to give a dilution series that extended from 24 to 0.375 ng of total RNA. Each reaction mixture contained a constant amount of the truncated -, ß-, -ENaC or cytokeratin 18 (CK18) cRNA as a competitive internal standard. The primers used and the reaction conditions for the RT and PCR reactions were as described previously.^16,20 PCR products were separated by electrophoresis, stained with ethidium bromide, and quantified using a charged coupled device camera and SCION Image software. ENaC and CK18 mRNA concentrations were calculated (in attomoles per microgram of total RNA) as described.²⁰ The ENaC expression of each sample was normalized against that of CK18, which was used as an epithelial marker (ENaC: CK18, attomole per femtomole).

Statistical Analysis
Patients’ clinical data are presented as mean ± standard deviation. QRT-PCR was done in duplicate for each target mRNA in each sample; assay results were averaged and the mean was used as a single datum. The normalized assay data (ENaC/CK18) are presented as mean ± standard deviation. Comparisons were performed with the Mann-Whitney U test. P < .05 was considered statistically significant.

	RESULTS

TOP ABSTRACT METHODS RESULTS DISCUSSION REFERENCES

 
The subunits -, ß-, and -hENaC and CK18 mRNA were found in all samples. We found that expression of all 3 hENaC subunits in the nasal epithelium were significantly lower in preterm infants relative to healthy term infants. In healthy term infants, -hENaC mRNA was 9.1 ± 2.3, ß-hENaC mRNA was 4.3 ± 1.1, and -hENaC mRNA was 6.8 ± 3.2 amol/fmol CK18 (Fig 1). In the preterm infants, -hENaC mRNA was 5.4 ± 2.0, ß-hENaC mRNA was 2.4 ± 1.4, and -hENaC mRNA was 2.4 ± 0.1 amol/fmol CK18 (Fig 1). The expression of each subunit was significantly higher in term than in preterm infants (P < .05)

View larger version (17K): [in this window] [in a new window]   Fig 1. Expression of - (A), ß- (B), and - (C) ENaC subunits in nasal epithelium in newborn preterm (n = 5) and term (n = 7) infants. ENaC subunit and CK18 mRNA was quantified in each sample as described in the text and previously.20 Data were normalized for epithelial cell content by dividing ENaC subunit mRNA concentration by CK18 mRNA concentration for the corresponding sample. Box plots represent the data from 5 (preterm) or 7 (term) subjects (center line median, extent of box 25th and 75th percentile).

View larger version (18K): [in this window] [in a new window]   Fig 2. Expression of - (A), ß- (B), and - (C) ENaC subunits in nasal epithelium in 4 preterm infants before (basal) and 7 to 20 hours after the commencement of dexamethasone treatment (treated). ENaC subunit and CK18 mRNA was quantified in each sample as described in the text and previously.20 Data were normalized for epithelial cell content by dividing the amount of ENaC subunit mRNA by the sample CK18 mRNA.

	DISCUSSION

TOP ABSTRACT METHODS RESULTS DISCUSSION REFERENCES

The role of hENaC function in neonatal RDS has not been elucidated fully. In rodents, ENaC mRNA expression in the lung has been correlated to gestational age.^25–27 Mouse models indicate that the -ENaC subunit is essential for lung fluid clearance at birth, whereas ß- and -ENaC knockout mice, which die as a result of renal insufficiency, display only a mild lung phenotype.^11,28 In contrast to laboratory animals, patients with the recessive systemic pseudohypoaldosteronism type I, who carry a loss-of-function mutation in hENaC - or ß-subunit or their regulatory regions, do not develop neonatal respiratory disease.^25,29–32 However, the later lung phenotype of these patients includes recurrent respiratory infections, increased volume of airway surface liquid, and absence of amiloride-sensitive sodium transport in the nasal epithelium, indicating an impact of the hENaC mutations on lung fluid balance. Despite lower basal readings within their nasal turbinates, these patients demonstrate inhibition of transepithelial PD after topical amiloride that is compatible with reduced but existing hENaC activity.³¹ Although -ENaC has been considered as a vital subunit for channel function, recent experimental data have demonstrated that defective -ENaC subunits when coexpressed with the other subunits are able to produce significant channel activity in Xenopus oocytes.³⁰ It thus is possible that mutant ENaC subunits or other compensatory mechanisms such as increased mucociliary function are sufficient to support lung fluid clearance, explaining the lack of neonatal RDS in patients with systemic pseudohypoaldosteronism type I.^30,31

Although expression of all 3 subunits is required for maximal channel activity, in Xenopus oocytes, the coexpression of only 2 subunits of the ENaC channel as :- or :ß-ENaC results in appreciable transmembrane sodium conductance; the biophysical properties of such versus ß channels differ significantly in terms of single-channel conductance, Na⁺ selectivity, and amiloride sensitivity.³³ Additional evidence exists suggesting unique roles for the ß and subunits, including a recent publication that suggested that the subunit is more important for channel surface expression than the ß subunit.³⁴

ENaC subunit mRNA expression varies quantitatively along the respiratory tract in adult humans.¹⁶ Only qualitative data are available on human fetal and neonatal airway, demonstrating constitutive expression of -hENaC mRNA throughout lung development.³⁵ In utero, the entire airway epithelium is likely to be under a homogeneous humoral and local ontogenic regulation, and in fact previous data have demonstrated that nasal epithelial function shows a correlation with neonatal lung disease, supporting the idea that it can be used as a surrogate for lung epithelium.^8,36 Therefore, we think that the present observation of low expression of all hENaC subunits in the nasal epithelia of preterm infants with RDS is important, and its comparison with previous investigations highlights interesting points. Both full-term and preterm infants express considerably less - and ß-hENaC mRNA than adults.¹⁶ In contrast, the expression of -hENaC seems to peak at term gestation, with much lower levels in both preterm infants and adults. -ENaC thus is expressed at markedly greater levels than ß- and -ENaC mRNA in adult respiratory tract epithelia: we observed mRNA ratios of 20:4:1 in human²⁰ and 50:1:5 in mouse nasal turbinate³⁷ by competitive QRT-PCR. The ratio of :ß: mRNA observed within the infants included in this study was 2:1:1 and resembles the predicted protein stoichiometry (2ß) presented previously.³⁸ This suggests that posttranscriptional steps may be regulated differently in the newborn compared with the adult respiratory epithelium.

Preterm infants whose mother has received betamethasone ante partum show improved postnatal pulmonary adaptation compared with infants of untreated mothers.³⁹ The mothers of all preterm infants in our study had received betamethasone, yet these infants expressed lower levels of hENaC mRNA than full-term infants, suggesting that the "basal" level of hENaC in untreated preterm infants may be even lower. Dexamethasone treatment of the 4 infants with prolonged ventilator dependence in our study was efficacious in improving fraction of inspired oxygen dependence, as illustrated in Table 2, and all 4 were weaned from the ventilator within 5 days of initiating steroid treatment.

Previous studies have shown that glucocorticoid treatment in newborn infants increases dynamic lung compliance and expiratory time constant and decreases total pulmonary resistance after 12 hours of treatment.⁴⁰ Glucocorticoid treatment improves pulmonary mechanics and gas exchange in a significant number of preterm infants with prolonged dependence on assisted ventilation.⁴¹ There are many potential mechanisms whereby postnatal glucocorticoid treatment could improve lung function. These may include anti-inflammatory effects, increases in surfactant production, and induction of ENaC (for review, see ref ⁴¹). In test conditions, glucocorticoid treatment increases clearance of pulmonary edema in adult rats and -ENaC expression in the fetal rat lung.^25,42 Significant differences seem to exist, however, in the ontogeny and glucocorticoid regulation of ENaC expression in lung between rodent and human. Both Northern and in situ hybridization analysis of developing rat and mouse lung indicate that ENaC subunit mRNAs are expressed only late in gestation, whereas in humans, hENaC mRNA has been detected in all airway epithelia from the earliest fetal lung bud stage onward.^25–27,43 In this study, we focused on the effects of dexamethasone on ENaC mRNAs in premature infants with prolonged RDS. This report represents the first assessment of glucocorticoid effects on ENaC synthesis in human infants and indicates that both the and ß subunits seem to be upregulated by dexamethasone. -hENaC mRNA was increased in 3 of the 4 infants. Our findings suggest that glucocorticoid induces transepithelial sodium movement through pathways such as ENaC, which may represent 1 mechanism whereby glucocorticoids improve pulmonary function of the preterm infants. Accordingly, it would be important, indeed, to find out by direct in situ measurements in a larger group of clinical patients whether the increased expression of hENaC subunits after glucocorticoid therapy correlates with an increased amiloride-sensitive transepithelial PD in the nasal turbinate.

Our study included newborn premature infants whose gestational age ranged from 26 to 28 weeks. At this stage of maturity, the infants are regularly born with respiratory distress, and finding proper nonaffected infants of similar antenatal history is difficult. In addition, other factors than mere mRNA content may participate in the regulation of the functional Na⁺ channels. These include increased translational efficiency by mRNA stabilization and differences in posttranslational assembly of the subunits in the membrane. Nevertheless, the present data support the hypothesis that neonatal RDS is associated with reduced ENaC expression. Surprising is that in preterm infants with prolonged ventilatory dependence, the -hENaC mRNA (amol/fmol CK18) ratio was higher and showed greater interindividual variation in comparison with preterm infants’ samples obtained within 5 hours of birth. The increased expression of -hENaC may reflect postnatal maturation of the airway epithelium. These infants had been exposed to nasotracheal intubation with the opposite side serving as the route for suction of the nasopharyngeal secretions. Also, the side of sample collection had to accommodate the nasogastric feeding tube. In addition to postnatal age, factors including inhaled oxygen concentration, circulating catecholamines induced by prolonged stress, and cell turnover as a result of local trauma during intubation may have affected hENaC and CK18 mRNA expression.^6,44,45 These factors preclude drawing firm conclusions when comparing hENaC mRNA expression in infants sampled soon after birth with infants under prolonged ventilation but do not invalidate our observation of increased hENaC mRNA expression in vivo in response to dexamethasone treatment. Of note is that the hENaC subunit values measured in these chronically ventilator-dependent infants were in the range of those reported in adults in an earlier paper by our research group.¹⁶

In conclusion, in newborn preterm infants with RDS, the expression of all subunits of hENaC in respiratory epithelium is significantly lower than in healthy term infants. Our findings suggest that the human upper airway epithelial hENaC expression and hence Na⁺ transport are developmentally regulated and can be augmented by treatment with the glucocorticoid dexamethasone. The present findings call for additional studies to elucidate whether in the preterm infant respiratory distress can be alleviated by therapeutic induction of hENaC.

	ACKNOWLEDGMENTS

 
This work was supported by Wilhelm och Else Stockmanns Stiftelse, the Foundation for Pediatric Research, Finska Läkaresällskapet, Sigrid Jusélius Foundation, the Special Governmental Subsidy for Health Sciences, the Ontario Thoracic Society, the Canadian Institutes in Health Research group Grant in Lung Biology, and the Hospital for Sick Children (Toronto).

We thank the personnel of the neonatal unit of the Hospital for Children and Adolescents for kind cooperation; Marita Suni, Marjatta Vallas, and Yanxia Wen for excellent technical assistance; and the Pediatric Graduate School of the University of Helsinki for support.

	FOOTNOTES

 
Received for publication Jan 17, 2003; Accepted Jul 14, 2003.

Reprint requests to (O.H.) Hospital for Children and Adolescents, University of Helsinki, Biomedicum B429b, PO Box 700, FIN-00029 HUS, Finland. E-mail: otto.helve{at}hus.fi

	REFERENCES

TOP ABSTRACT METHODS RESULTS DISCUSSION REFERENCES

 

1. Strang LB. Fetal lung liquid: secretion and reabsorption. Physiol Rev. 1991;71 :991 –1016[Free Full Text]
2. Pitkanen OM, O’Brodovich HM. Significance of ion transport during lung development and in respiratory disease of the newborn. Ann Med. 1998;30 :134 –142[ISI][Medline]
3. O’Brodovich H. Epithelial ion transport in the fetal and perinatal lung. Am J Physiol. 1991;261(suppl) :C555 –C564
4. Olver RE, Strang LB. Ion fluxes across the pulmonary epithelium and the secretion of lung liquid in the foetal lamb. J Physiol. 1974;241 :327 –357[Abstract/Free Full Text]
5. Brown MJ, Olver RE, Ramsden CA, Strang LB, Walters DV. Effects of adrenaline and of spontaneous labour on the secretion and absorption of lung liquid in the fetal lamb. J Physiol. 1983;344 :137 –152[Abstract/Free Full Text]
6. Pitkanen O, Transwell AK, Downey G, O’Brodovich H. Increased Po2 alters the bioelectric properties of fetal distal lung epithelium. Am J Physiol. 1996;270(suppl) :L1060 –L1066
7. Bland RD, Nielson DW. Developmental changes in lung epithelial ion transport and liquid movement. Annu Rev Physiol. 1992;54 :373 –394[CrossRef][ISI][Medline]
8. Barker PM, Gowen CW, Lawson EE, Knowles MR. Decreased sodium ion absorption across nasal epithelium of very premature infants with respiratory distress syndrome. J Pediatr. 1997;130 :373 –377[CrossRef][ISI][Medline]
9. Canessa CM, Schild L, Buell G, et al. Amiloride-sensitive epithelial Na+ channel is made of three homologous subunits. Nature. 1994;367 :463 –467[CrossRef][Medline]
10. O’Brodovich H, Hannam V, Seear M, Mullen JB. Amiloride impairs lung water clearance in newborn guinea pigs. J Appl Physiol. 1990;68 :1758 –1762[Abstract/Free Full Text]
11. Hummler E, Barker P, Gatzy J, et al. Early death due to defective neonatal lung liquid clearance in alpha-ENaC-deficient mice. Nat Genet. 1996;12 :325 –328[CrossRef][ISI][Medline]
12. Venkatesh VC, Katzberg HD. Glucocorticoid regulation of epithelial sodium channel genes in human fetal lung. Am J Physiol. 1997;273(suppl) :L227 –L233
13. Sayegh R, Auerbach SD, Li X, et al. Glucocorticoid induction of epithelial sodium channel expression in lung and renal epithelia occurs via trans-activation of a hormone response element in the 5'-flanking region of the human epithelial sodium channel alpha subunit gene. J Biol Chem. 1999;274 :12431 –12437[Abstract/Free Full Text]
14. Thomas CP, Auerbach SD, Zhang C, Stokes JB. The structure of the rat amiloride-sensitive epithelial sodium channel gamma subunit gene and functional analysis of its promoter. Gene. 1999;228 :111 –122[CrossRef][ISI][Medline]
15. Lazrak A, Samanta A, Venetsanou K, Barbry P, Matalon S. Modification of biophysical properties of lung epithelial Na(+) channels by dexamethasone. Am J Physiol Cell Physiol. 2000;279 :C762 –C770[Abstract/Free Full Text]
16. Pitkanen OM, Smith D, O’Brodovich H, Otulakowski G. Expression of alpha-, beta-, and gamma-hENaC mRNA in the human nasal, bronchial, and distal lung epithelium. Am J Respir Crit Care Med. 2001;163 :273 –276[Abstract/Free Full Text]
17. Knowles M, Gatzy J, Boucher R. Increased bioelectric potential difference across respiratory epithelia in cystic fibrosis. N Engl J Med. 1981;305 :1489 –1495[Abstract]
18. Jorissen M, Bertrand B, Eloy P. Ciliary dyskinesia in the nose and paranasal sinuses. Acta Otorhinolaryngol Belg. 1997;51 :353 –366[Medline]
19. Knowles MR, Carson JL, Collier AM, Gatzy JT, Boucher RC. Measurements of nasal transepithelial electric potential differences in normal human subjects in vivo. Am Rev Respir Dis. 1981;124 :484 –490[ISI][Medline]
20. Otulakowski G, Flueckiger-Staub S, Ellis L, et al. Relation between alpha, beta, and gamma human amiloride-sensitive epithelial Na+ channel mRNA levels and nasal epithelial potential difference in healthy men. Am J Respir Crit Care Med. 1998;158 :1213 –1220[Abstract/Free Full Text]
21. Avery M, Mead J. Surface properties in relation to atelectasis and hyaline membrane disease. Am J Dis Child. 1959;97 :517 –523
22. Jobe AH. Pulmonary surfactant therapy. N Engl J Med. 1993;328 :861 –868[Free Full Text]
23. O’Brodovich HM. Immature epithelial Na+ channel expression is one of the pathogenetic mechanisms leading to human neonatal respiratory distress syndrome. Proc Assoc Am Physicians. 1996;108 :345 –355[ISI][Medline]
24. DeSa DJ. Pulmonary fluid content in infants with respiratory distress. J Pathol. 1969;97 :469 –478[CrossRef][ISI][Medline]
25. Tchepichev S, Ueda J, Canessa C, Rossier BC, O’Brodovich H. Lung epithelial Na channel subunits are differentially regulated during development and by steroids. Am J Physiol. 1995;269(suppl) :C805 –C812
26. O’Brodovich H, Canessa C, Ueda J, Rafii B, Rossier BC, Edelson J. Expression of the epithelial Na+ channel in the developing rat lung. Am J Physiol. 1993;265(suppl) :C491 –C496
27. Dagenais A, Kothary R, Berthiaume Y. The alpha subunit of the epithelial sodium channel in the mouse: developmental regulation of its expression. Pediatr Res. 1997;42 :327 –334[ISI][Medline]
28. McDonald FJ, Yang B, Hrstka RF, et al. Disruption of the beta subunit of the epithelial Na+ channel in mice: hyperkalemia and neonatal death associated with a pseudohypoaldosteronism phenotype. Proc Natl Acad Sci U S A. 1999;96 :1727 –1731[Abstract/Free Full Text]
29. Bonny O, Rossier BC. Disturbances of Na/K balance: pseudohypoaldosteronism revisited. J Am Soc Nephrol. 2002;13 :2399 –2414[Free Full Text]
30. Bonny O, Chraibi A, Loffing J, et al. Functional expression of a pseudohypoaldosteronism type I mutated epithelial Na+ channel lacking the pore-forming region of its alpha subunit. J Clin Invest. 1999;104 :967 –974[ISI][Medline]
31. Kerem E, Bistritzer T, Hanukoglu A, et al. Pulmonary epithelial sodium-channel dysfunction and excess airway liquid in pseudohypoaldosteronism. N Engl J Med. 1999;341 :156 –162[Abstract/Free Full Text]
32. Thomas CP, Zhou J, Liu KZ, Mick VE, MacLaughlin E, Knowles M. Systemic pseudohypoaldosteronism from deletion of the promoter region of the human beta epithelial na(+) channel subunit. Am J Respir Cell Mol Biol. 2002;27 :314 –319[Abstract/Free Full Text]
33. McNicholas CM, Canessa CM. Diversity of channels generated by different combinations of epithelial sodium channel subunits. J Gen Physiol. 1997;109 :681 –692[Abstract/Free Full Text]
34. Konstas AA, Korbmacher C. The gamma-subunit of ENaC is more important for channel surface expression than the beta-subunit. Am J Physiol Cell Physiol. 2003;284 :C447 –C456[Abstract/Free Full Text]
35. Smith DE, Otulakowski G, Yeger H, Post M, Cutz E, O’Brodovich HM. Epithelial Na(+) channel (ENaC) expression in the developing normal and abnormal human perinatal lung. Am J Respir Crit Care Med. 2000;161(suppl) :1322 –1331
36. Gowen CW Jr, Lawson EE, Gingras J, Boucher RC, Gatzy JT, Knowles MR. Electrical potential difference and ion transport across nasal epithelium of term neonates: correlation with mode of delivery, transient tachypnea of the newborn, and respiratory rate. J Pediatr. 1988;113(suppl) :121 –127
37. Kassovska-Bratinova S, Vannam V, Freywald T, Otulakowski G, O’Brodovich H. Absence of detectable amiloride-sensitive ion transport in murine tracheal epithelia may result from lack of beta-ENaC mRNA expression. Am J Respir Crit Care Med. 2000;161 :A234
38. Firsov D, Gautschi I, Merillat AM, Rossier BC, Schild L. The heterotetrameric architecture of the epithelial sodium channel (ENaC). EMBO J. 1998;17 :344 –352[CrossRef][ISI][Medline]
39. Wright LL, Horbar JD, Gunkel H, et al. Evidence from multicenter networks on the current use and effectiveness of antenatal corticosteroids in low birth weight infants. Am J Obstet Gynecol. 1995;173 :263 –269[CrossRef][ISI][Medline]
40. Gladstone IM, Ehrenkranz RA, Jacobs HC. Pulmonary function tests and fluid balance in neonates with chronic lung disease during dexamethasone treatment. Pediatrics. 1989;84 :1072 –1076[Abstract/Free Full Text]
41. Bancalari E. Corticosteroids and neonatal chronic lung disease. Eur J Pediatr. 1998;157(suppl 1) :S31 –S37
42. Folkesson HG, Norlin A, Wang Y, Abedinpour P, Matthay MA. Dexamethasone and thyroid hormone pretreatment upregulate alveolar epithelial fluid clearance in adult rats. J Appl Physiol. 2000;88 :416 –424[Abstract/Free Full Text]
43. Talbot CL, Bosworth DG, Briley EL, et al. Quantitation and localization of ENaC subunit expression in fetal, newborn, and adult mouse lung. Am J Respir Cell Mol Biol. 1999;20 :398 –406[Abstract/Free Full Text]
44. Rafii B, Tanswell AK, Pitkanen O, O’Brodovich H. Induction of epithelial sodium channel (ENaC) expression and sodium transport in distal lung epithelia by oxygen. Curr Top Membr. 1999;47 :239 –244
45. Minakata Y, Suzuki S, Grygorczyk C, Dagenais A, Berthiaume Y. Impact of beta-adrenergic agonist on Na+ channel and Na+-K+-ATPase expression in alveolar type II cells. Am J Physiol. 1998;275(suppl) :L414 –L422

This article has been cited by other articles:

				B. H. Lee, B. J. Stoll, S. A. McDonald, R. D. Higgins, and for the National Institute of Child Health and Hum Neurodevelopmental Outcomes of Extremely Low Birth Weight Infants Exposed Prenatally to Dexamethasone Versus Betamethasone Pediatrics, February 1, 2008; 121(2): 289 - 296. [Abstract] [Full Text] [PDF]

				O. Helve, C. Janer, O. Pitkanen, and S. Andersson Expression of the Epithelial Sodium Channel in Airway Epithelium of Newborn Infants Depends on Gestational Age Pediatrics, December 1, 2007; 120(6): 1311 - 1316. [Abstract] [Full Text] [PDF]

				R. R. Quesnell, X. Han, and B. D. Schultz Glucocorticoids stimulate ENaC upregulation in bovine mammary epithelium Am J Physiol Cell Physiol, May 1, 2007; 292(5): C1739 - C1745. [Abstract] [Full Text] [PDF]

				B. H. Lee, B. J. Stoll, S. A. McDonald, R. D. Higgins, and for the National Institute of Child Health and Hum Adverse Neonatal Outcomes Associated With Antenatal Dexamethasone Versus Antenatal Betamethasone Pediatrics, May 1, 2006; 117(5): 1503 - 1510. [Abstract] [Full Text] [PDF]

				A. M. Woollhead and D. L. Baines Forskolin-induced Cell Shrinkage and Apical Translocation of Functional Enhanced Green Fluorescent Protein-Human {alpha}ENaC in H441 Lung Epithelial Cell Monolayers J. Biol. Chem., February 24, 2006; 281(8): 5158 - 5168. [Abstract] [Full Text] [PDF]

				O. Helve, S. Andersson, T. Kirjavainen, and O. M. Pitkanen Improvement of Lung Compliance during Postnatal Adaptation Correlates with Airway Sodium Transport Am. J. Respir. Crit. Care Med., February 15, 2006; 173(4): 448 - 452. [Abstract] [Full Text] [PDF]

				N. Elias and H. O'Brodovich Clearance of Fluid From Airspaces of Newborns and Infants NeoReviews, February 1, 2006; 7(2): e88 - e94. [Full Text] [PDF]

				K. Banasikowska, M. Post, E. Cutz, H. O'Brodovich, and G. Otulakowski Expression of epithelial sodium channel {alpha}-subunit mRNAs with alternative 5'-untranslated regions in the developing human lung Am J Physiol Lung Cell Mol Physiol, September 1, 2004; 287(3): L608 - L615. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) P3Rs: Submit a response Alert me when this article is cited Alert me when P3Rs are posted Alert me if a correction is posted Citation Map Services E-mail this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Add to My File Cabinet Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via ISI Web of Science (15) Citing Articles via Google Scholar Google Scholar Articles by Helve, O. Articles by Otulakowski, G. Search for Related Content PubMed PubMed Citation Articles by Helve, O. Articles by Otulakowski, G. Related Collections Premature & Newborn

	Home | My Pediatrics | Journal Information | Current Issue | Past Issues | Subscriptions & Services | Contact Us Click here for faster international access © 2004 American Academy of Pediatrics. All rights reserved.