Nuclear Na+/K+-ATPase plays an active role in nucleoplasmic Ca2+ homeostasis.
Na(+)/K(+)-ATPase, an integral membrane protein, has been studied for over a half century with respect to its transporter function in the plasma membrane, where it expels three Na(+) ions from the cell in exchange for two K(+) ions. In this study, we demonstrate a functioning Na(+)/K(+)-ATPase within HEK293 cell nuclei. This subcellular localization was confirmed by western blotting, ouabain-sensitive ATPase activity of the nuclear membrane fraction, immunocytochemistry and delivery of fluorescently tagged Na(+)/K(+)-ATPase α- and β-subunits. In addition, we observed an overlap between nuclear Na(+)/K(+)-ATPase and Na/Ca-exchanger (NCX) when nuclei were immunostained with commercially available Na(+)/K(+)-ATPase and NCX antibodies, suggesting a concerted physiological coupling between these transporters. In keeping with this, we observed an ATP-dependent, strophanthidin-sensitive Na(+) flux into the nuclear envelope (NE) lumen loaded with the Na-sensitive dye, CoroNa-Green. Analogous experiments using Fluo-5N, a low affinity Ca(2+) indicator, demonstrated a similar ATP-dependent and strophanthidin-sensitive Ca(2+) flux into the NE lumen. Our results reveal an intracellular physiological role for the coordinated efforts of the Na(+)/K(+)-ATPase and NCX to actively remove Ca(2+) from the nucleoplasm into the NE lumen (i.e. the nucleoplasmic reticulum).
School of Biological Sciences, Illinois State University, Normal, IL 61790-4120, USA.
Charitha
C
Galva
Pablo
P
Artigas
Craig
C
Gatto
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002467:Cell Nucleus / Q000201:enzymology / Q000378:metabolism*; D057809:HEK293 Cells; D006706:Homeostasis; D006801:Humans; D012756:Sheep; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium