Mechanisms of EGF-induced stimulation of sodium reabsorption by alveolar epithelial cells.
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) alpha-, beta-, and gamma-subunits and Na+ pump alpha1- and beta1-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 alpha1 and beta1 Na+ pump subunit mRNA but no increase in rENaC subunit mRNA. EGF-treated monolayers showed parallel increases in Na+ pump alpha1- and beta1-subunit protein by immunoblot relative to untreated monolayers. Fixed AEC monolayers demonstrated predominantly membrane-associated immunofluorescent labeling with anti-Na+ pump alpha1- and beta1-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.
Will Rogers Institute Pulmonary Research Center, Division of Pulmonary and Critical Care Medicine, University of Southern California, Los Angeles, California 90033, USA.
S I
SI
Danto
Z
Z
Borok
X L
XL
Zhang
M Z
MZ
Lopez
P
P
Patel
E D
ED
Crandall
R L
RL
Lubman
D000818:Animals; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D053503:Epithelial Sodium Channels; D005786:Gene Expression Regulation / Q000187:drug effects*; D007700:Kinetics; D046911:Macromolecular Substances; D008297:Male; D011650:Pulmonary Alveoli / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000096:biosynthesis*; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis*; D014158:Transcription, Genetic
D016895:Culture Media, Serum-Free; D053503:Epithelial Sodium Channels; D046911:Macromolecular Substances; D012333:RNA, Messenger; D015222:Sodium Channels; D004815:Epidermal Growth Factor; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase