Na+/K+-ATPase plays a key role in the transport of Na+ throughout the nephron, but ageing appears to be accompanied by changes in the regulation and localization of the pump. In the present study, we examined the effect of in vitro cell ageing on the transport of Na+ and K+ ions in opossum kidney (OK) cells in culture. Cells were aged by repeated passing, and Na+/K+-ATPase activity and K+ conductance were evaluated using electrophysiological methods. Na+K+-ATPase α1– and β1-subunit expression was quantified by Western blot techniques. Na+/H+ exchanger activity, changes in membrane potential, cell viability, hydrogen peroxide production and cellular proliferation were determined using fluorimetric assays. In vitro cell ageing is accompanied by an increase in transepithelial Na+ transport, which results from an increase in the number of Na+/K+-ATPase α1- and β1-subunits, in the membrane. Increases in Na+/K+-ATPase activity were accompanied by increases in K+ conductance as a result of functional coupling between Na+/K+-ATPase and basolateral K+ channels. Cell depolarization induced by both KCl and ouabain was more pronounced in aged cells. No changes in Na+/H+ exchanger activity were observed. H2O2 production was increased in aged cells, but exposure for 5 days to 1 and 10 μM of H2O2 had no effect on Na+/K+-ATPase expression. Ouabain (100 nM) increased α1-subunit, but not β1-subunit, Na+/K+-ATPase expression in aged cells only. These cells constitute an interesting model for the study of renal epithelial cell ageing.
The Journal of Membrane Biology – Springer Journals
Published: Feb 28, 2007
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