title: Cardiotonic steroid-resistant alpha1-Na+,K+-ATPase rescues renal epithelial cells from the cytotoxic action of ouabain: evidence for a Nai+,Ki+ -independent mechanism.
abstract: Mechanisms underlying the tissue-specific impact of cardiotonic steroids (CTS) on cell survival and death remain poorly understood. This study examines the role of Na(+),K(+)-ATPase alpha subunits in death of Madin-Darby canine kidney (MDCK) cells evoked by 24-h exposure to ouabain. MDCK cells expressing a variant of the alpha1 isoform, CTS-sensitive alpha1S, were stably transfected with a cDNA encoding CTS-resistant alpha1R-Na(+),K(+)-ATPase, whose expression was confirmed by RT-PCR. In mock-transfected and alpha1R-cells, maximal inhibition of (86)Rb influx was observed at 10 and 1000 muM ouabain, respectively, thus confirming high abundance of alpha1R-Na(+),K(+)-ATPase in these cells. Six-hour treatment of alpha1R-cells with 1000 muM ouabain led to the same elevation of the [Na(+)](i)/[K(+)](i) ratio that was detected in mock-transfected cells treated with 3 muM ouabain. However, in contrast to the massive death of mock-transfected cells exposed to 3 muM ouabain, alpha1R-cells survived after 24-h incubation with 1000 muM ouabain. Inversion of the [Na(+)](i)/[K(+)](i) ratio evoked by Na(+),K(+)-ATPase inhibition in K(+)-free medium did not affect survival of alpha1R-cells but increased their sensitivity to ouabain. Our results show that the alpha1R subunit rescues MDCK cells from the cytotoxic action of CTS independently of inhibition of Na(+),K(+)-ATPase-mediated Na(+) and K(+) fluxes and inversion of the [Na(+)](i)/[K(+)](i) ratio.
authors: Centre de Recherche, Centre Hospitalier de l'Université de Montréal, Technopôle Angus, 2901 Rachel Est, Montreal, QC H1W 4A4, Canada. ol_akimova@hotmail.com
authors: Olga A
authors: OA
authors: Akimova
authors: Johanne
authors: J
authors: Tremblay
authors: James W
authors: JW
authors: Van Huysse
authors: Pavel
authors: P
authors: Hamet
authors: Sergei N
authors: SN
authors: Orlov
mesh_terms: D000818:Animals; D002301:Cardiac Glycosides / Q000737:chemistry*; D002460:Cell Line; D004285:Dogs; D004791:Enzyme Inhibitors / Q000737:chemistry*; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology*; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D010042:Ouabain / Q000633:toxicity*; D011188:Potassium / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D002301:Cardiac Glycosides; D004791:Enzyme Inhibitors; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium