Purchase this article with an account.
Liora Shoshani, Jorge A. Lobato-Alvarez, Norberto F. Hernandez-Llanes, Maria-Luisa Roldan, Abelardo A. Rodriguez-Reyes; Polarization Of Na+,K+-ATPase In Retina Pigment Epithelium (RPE); Role Of β-subunit. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6668.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Na+/K+- ATPase, the sodium pump is an ion transporter that plays a central role in maintaining the sodium gradient responsible for transport of virtually all nutrients and metabolites. In epithelial monolayers Na+/K+- ATPase is enriched to a cell membrane-specific domain. Pump polarity is achieved by a complex sequence of events involving both targeting to and selective retention at the lateral cell membrane. In contrast to the majority of epithelial cell models, the sodium pump is enriched in the apical membrane domain of RPE cells. This ‘reverse polarity’ of the RPE was brought to our attention given that the polarization mechanism of Na-pump is still not clear. Our working hypothesis is that the pump polarity in RPE cells is regulated by its β–subunit and more precisely by the type of isoform that is expressed. In this study we have examined and compared the expression patterns of the three known isoforms of Na+,K+-ATPase β-subunits (β1, β2 and β3) in the cell line ARPE-19.
Western blot (WB) and immunofluorescence (IF) studies were carried using established human RPE cell line, ARPE-19, that were cultured for 8 weeks on laminin covered clear inserts. The expression of β1, β2 and β3 isoforms was determined by WB. The membrane localization of each isoform was determined by IF, staining with specific antibodies for each isoform.
The expression of the different isoforms was time and domain dependent. All three isoforms (β1, β2 and β3) were detected. Nevertheless, while β1 subunit was detected during all 8 weeks the expression of β2 and β3 subunits was up-regulated during re-morphogenesis; both are absent during the first three weeks and appears around the 4th week and thereafter as detected by WB and IF. While β1 and β3 are expressed mainly on basolateral membrane β2 is observed on apical membrane.
This is the first expression study of all three β subunits isoforms in RPE cells. Our results indicate that the apical localization of the sodium pump in RPE is probably related to the expression of β2 subunit, which carries a dominant apical sorting information.
This PDF is available to Subscribers Only