title: Evidence for epidermal growth factor receptor as negative-feedback control in aldosterone-induced Na+ reabsorption.
abstract: Aldosterone enhances Na(+) reabsorption via epithelial Na(+) channels (ENaC). Aldosterone also stimulates the protein kinase ERK1/2- and the epidermal growth factor (EGF) receptor (EGFR)-signaling pathway. Yet EGF and ERK1/2 are known inhibitors of ENaC-mediated Na(+) reabsorption. In the present study, using the well-established Madin-Darby canine kidney C7 cell line, we tested the hypothesis that EGFR represents a negative-feedback control for chronic aldosterone-induced Na(+) reabsorption [amiloride-inhibitable short-circuit current (I(sc))]. Mineralocorticoid receptor expression was confirmed by RT-PCR and Western blot analysis. Aldosterone enhanced ERK1/2 phosphorylation in an EGFR-dependent way. Furthermore, aldosterone stimulated EGFR expression. Aldosterone (10 nmol/l) induced a small transient increase in I(sc) under control conditions. Inhibition of ERK1/2 phosphorylation with U-0126 (10 micromol/l) stimulated I(sc), indicating constitutive ENaC inhibition. Aldosterone exerted a significantly larger effect in the presence of U-0126 than without U-0126. EGF (10 microg/l) inhibited I(sc), whereas inhibition of EGFR kinase by tyrphostin AG-1478 (100 nmol/l) enhanced I(sc). Aldosterone was more effective in the presence of AG-1478 than without AG-1478. In summary, we propose that the EGFR-signaling cascade can serve as a negative-feedback control to limit the effect of aldosterone-induced Na(+) reabsorption.
authors.affiliation: Physiologisches Institut, Universität Würzburg, Röntgenring 9, 97070 Würzburg, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Grossmann
authors.forename: Ruth
authors.initials: R
authors.lastname: Freudinger
authors.forename: Sigrid
authors.initials: S
authors.lastname: Mildenberger
authors.forename: Alexander W
authors.initials: AW
authors.lastname: Krug
authors.forename: Michael
authors.initials: M
authors.lastname: Gekle
mesh_terms: D000450:Aldosterone / Q000494:pharmacology*; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D004285:Dogs; D004797:Enzyme-Linked Immunosorbent Assay; D053503:Epithelial Sodium Channels; D066246:ErbB Receptors / Q000502:physiology*; D005246:Feedback / Q000502:physiology; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism / Q000502:physiology
chemical_list: D053503:Epithelial Sodium Channels; D015222:Sodium Channels; D000450:Aldosterone; D012964:Sodium; D066246:ErbB Receptors; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases