Abstract
The cytotoxic effect of long-term exposure of renal epithelial cells to ouabain and other cardiotonic steroids (CTS) is mediated by the interaction of these compounds with Na+,K+-ATPase but is independent of the inhibition of Na+,K+-ATPase-mediated ion fluxes. Sustained application of CTS also leads to Na+,K+-ATPase endocytosis and its translocation into the nuclei that might trigger the cell death machinery via the regulation of gene expression. This study examines the role of Na+,K+-ATPase internalization and de novo gene expression in the death of ouabain-treated C7-Madin–Darby canine kidney (MDCK) cells derived from distal tubules of the MDCK. In these cells, 6-h exposure to 3 μM ouabain led to the internalization of ∼50% of plasmalemmal Na+,K+-ATPase. Prolonged incubation in a K+-free medium abolished ouabain-induced Na+,K+-ATPase internalization but did not affect the cytotoxic action of ouabain seen after 18-h incubation. Previously, it was shown that CTS-induced Na+,K+-ATPase internalization is mediated by its interaction with Src within caveolae. Neither caveolae damage by cholesterol depletion with methyl-β-cyclodextrin nor Src inhibition with 4-amino-5(4-chlorophenyl)-7-(t-butyl)pyrazol[3,4-d]pyridine affected the death of ouabain-treated C7-MDCK cells. Actinomycin D at the 0.1-μg/ml concentration almost completely abolished ribonucleic acid synthesis but did not protect C7-MDCK cells from the cytotoxic action of ouabain. Our results show that neither Na+,K+-ATPase endocytosis nor de novo gene expression contributes to \( {\text{Na}}^{ + }_{i} ,{\text{K}}^{ + }_{i} \)-independent cell death signaling evoked by prolonged exposure to CTS.
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This work was supported by grants from the Canadian Institutes of Health Research, the Heart and Stroke Foundation of Canada, and the Kidney Foundation of Canada. The editorial help of Ovid Da Silva is appreciated.
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Akimova, O.A., Hamet, P. & Orlov, S.N. [Na+] i /[K+] i -independent death of ouabain-treated renal epithelial cells is not mediated by Na+,K+-ATPase internalization and de novo gene expression. Pflugers Arch - Eur J Physiol 455, 711–719 (2008). https://doi.org/10.1007/s00424-007-0283-6
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DOI: https://doi.org/10.1007/s00424-007-0283-6