title: Aldosterone inhibits apical NHE3 and HCO3- absorption via a nongenomic ERK-dependent pathway in medullary thick ascending limb.
abstract: Although aldosterone influences a variety of cellular processes through nongenomic mechanisms, the significance of nongenomic pathways for aldosterone-induced regulation of epithelial function is not understood. Recently, we demonstrated that aldosterone inhibits transepithelial HCO(3)(-) absorption in the medullary thick ascending limb (MTAL) through a nongenomic pathway. This inhibition is mediated through a direct cellular action of aldosterone to inhibit the apical membrane NHE3 Na(+)/H(+) exchanger. The present study was designed to identify the intracellular signaling pathway(s) responsible for this aldosterone-induced transport regulation. In rat MTALs perfused in vitro, addition of 1 nM aldosterone to the bath decreased HCO(3)(-) absorption by 30%. This inhibition was not mediated by cAMP/PKA and was not prevented by inhibitors of PKC or PI3-K, pertussis toxin, or rapamycin. The inhibition of HCO(3)(-) absorption by aldosterone was largely eliminated by the MEK/ERK inhibitors U-0126 and PD-98059. Aldosterone increased ERK activity 1.8-fold in microdissected MTALs. This ERK activation is rapid (</=5 min) and is blocked by U-0126 or PD-98059 but is unaffected by spironolactone or actinomycin D. Pretreatment with U-0126 to block ERK activation prevented the effect of aldosterone to inhibit apical NHE3. These data demonstrate that aldosterone inhibits NHE3 and HCO(3)(-) absorption in the MTAL through rapid activation of the ERK signaling pathway. The results identify NHE3 as a target for nongenomic regulation by aldosterone and establish a role for ERK in the acute regulation of NHE3 and its epithelial absorptive functions.
authors.affiliation: 4.200 John Sealy Annex, Univ. of Texas Medical Branch, 301 Univ. Boulevard, Galveston, TX 77555-0562, USA.
authors.forename: Bruns A
authors.initials: BA
authors.lastname: Watts
authors.forename: Thampi
authors.initials: T
authors.lastname: George
authors.forename: David W
authors.initials: DW
authors.lastname: Good
mesh_terms: D000450:Aldosterone / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D016764:Cell Polarity; D000242:Cyclic AMP / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D007679:Kidney Medulla / Q000378:metabolism; D008138:Loop of Henle / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D037342:Pertussis Toxin / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D011522:Protons; D051381:Rats; D017207:Rats, Sprague-Dawley; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*
chemical_list: D001639:Bicarbonates; D011522:Protons; C000613387:Slc9a3 protein, rat; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D000450:Aldosterone; D012964:Sodium; D000242:Cyclic AMP; D037342:Pertussis Toxin; D019869:Phosphatidylinositol 3-Kinases; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D011493:Protein Kinase C; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D019204:GTP-Binding Proteins