title: Ouabain stimulates Na-K-ATPase through a sodium/hydrogen exchanger-1 (NHE-1)-dependent mechanism in human kidney proximal tubule cells.
abstract: Recent investigations demonstrate increased Na/H exchanger-1 (NHE-1) activity and plasma levels of ouabain-like factor in spontaneously hypertensive rats. At nanomolar concentrations, ouabain increases Na-K-ATPase activity, induces cell proliferation, and activates complex signaling cascades. We hypothesize that the activity of NHE-1 and Na-K-ATPase are interdependent. To test whether treatment with picomolar ouabain regulates Na-K-ATPase through an NHE-1-dependent mechanism, we examined the role of NHE-1 in ouabain-mediated stimulation of Na-K-ATPase in kidney proximal tubule cell lines [opossum kidney (OK), HK-2, HKC-5, and HKC-11] and rat kidney basolateral membranes. Ouabain stimulated Na-K-ATPase activity and tyrosine phosphorylation in cells that express NHE-1 (OK, HKC-5, and HKC-11) but not in HK-2 cells that express very low levels of NHE-1. Inhibition of NHE-1 with 5 microM EIPA, a NHE-1-specific inhibitor, prevented ouabain-mediated stimulation of (86)Rb uptake and Na-K-ATPase phosphorylation in OK, HKC-5, and HKC-11 cells. Expression of wild-type NHE-1 in HK2 cells restored regulation of Na-K-ATPase by picomolar ouabain. Treatment with picomolar ouabain increased membrane expression of Na-K-ATPase and enhanced NHE-1-Na-K-ATPase alpha1-subunit association. Treatment with ouabain (1 microg x kg body wt(-1) x day(-1)) increased Na-K-ATPase activity, expression, phosphorylation, and association with NHE-1 increased in rat kidney cortical basolateral membranes. Eight days' treatment with ouabain (1 microg x kg body wt(-1) x day(-1)) resulted in increased blood pressure in these rats. These results suggest that the association of NHE-1 with Na-K-ATPase is critical for ouabain-mediated regulation of Na-K-ATPase and that these effects may play a role in cardioglycoside-stimulated hypertension.
authors.affiliation: Department of Medicine/Kidney Disease Program, University of Louisville, Louisville, Kentucky, USA.
authors.forename: Kristine A
authors.initials: KA
authors.lastname: Holthouser
authors.forename: Amritlal
authors.initials: A
authors.lastname: Mandal
authors.forename: Michael L
authors.initials: ML
authors.lastname: Merchant
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Schelling
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Delamere
authors.forename: Ronald R
authors.initials: RR
authors.lastname: Valdes
authors.forename: Suresh C
authors.initials: SC
authors.lastname: Tyagi
authors.forename: Eleanor D
authors.initials: ED
authors.lastname: Lederer
authors.forename: Syed J
authors.initials: SJ
authors.lastname: Khundmiri
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D006801:Humans; D006868:Hydrolysis; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000201:enzymology; D009893:Opossums; D010042:Ouabain / Q000494:pharmacology*; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection; D014443:Tyrosine
chemical_list: D027682:Cation Transport Proteins; C490998:SLC9A1 protein, human; C452850:Slc9a1 protein, rat; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; D014443:Tyrosine; D010042:Ouabain; D000584:Amiloride; D000255:Adenosine Triphosphate; C499076:ATP1A1 protein, human; C499075:Atp1a1 protein, rat; D000254:Sodium-Potassium-Exchanging ATPase; C039614:ethylisopropylamiloride