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

• Published in: American Journal of Physiology: Cell Physiology Vol. 275; no. 1; pp. C82 - C92
• Main Authors: Danto, Spencer I, Borok, Zea, Zhang, Xiao-Ling, Lopez, Melissa Z, Patel, Paryus, Crandall, Edward D, Lubman, Richard L
• Format: Journal Article
• Language: English
• Published: United States 01.07.1998
• Subjects: Animals; Cells, Cultured; Culture Media, Serum-Free; Epidermal Growth Factor - pharmacology; Epithelial Cells - cytology; Epithelial Cells - drug effects; Epithelial Cells - physiology; Epithelial Sodium Channels; Gene Expression Regulation - drug effects; Kinetics; Macromolecular Substances; Male; Pulmonary Alveoli - cytology; Pulmonary Alveoli - drug effects; Pulmonary Alveoli - physiology; Rats; Rats, Sprague-Dawley; RNA, Messenger - biosynthesis; Sodium - metabolism; Sodium Channels - biosynthesis; Sodium-Potassium-Exchanging ATPase - biosynthesis; Transcription, Genetic
• ISSN: 0363-6143; 0002-9513; 1522-1563
• DOI: 10.1152/ajpcell.1998.275.1.c82

Will Rogers Institute Pulmonary Research Center, Division of Pulmonary and Critical Care Medicine, University of Southern California, Los Angeles, California 90033 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) -, -, and -subunits and Na + pump 1 - and 1 -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 1 and 1 Na + pump subunit mRNA but no increase in rENaC subunit mRNA. EGF-treated monolayers showed parallel increases in Na + pump 1 - and 1 -subunit protein by immunoblot relative to untreated monolayers. Fixed AEC monolayers demonstrated predominantly membrane-associated immunofluorescent labeling with anti-Na + pump 1 - and 1 -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. alveolar epithelium; epidermal growth factor; gene expression; rat epithelial sodium channel; sodium-potassium-adenosine triphosphatase