Na-K-
ATPase located on the basolateral membrane (BLM) of intestinal epithelial cells provides a favorable intracellular Na+ gradient to promote all Na dependent co-transport processes across the brush border membrane (BBM). Down-regulation of Na-K-
ATPase activity has been postulated to alter the absorption via Na-solute
co-transporters in human
inflammatory bowel disease (IBD). Further, the altered activity of a variety of Na-solute
co-transporters in intact villus cells has been reported in animal models of chronic
enteritis. But the molecular mechanism of down-regulation of Na-K-
ATPase is not known. In the present study, using a rabbit model of chronic intestinal
inflammation, which resembles human IBD, Na-K-
ATPase in villus cells was shown to decrease. The relative
mRNA abundance of α-1 and β-1 subunits was not altered in villus cells during chronic intestinal
inflammation. Similarly, the
protein levels of these subunits were also not altered in villus cells during chronic
enteritis. However, the BLM concentration of α-1 and β-1 subunits was diminished in the chronically inflamed intestinal villus cells. An
ankyrin-
spectrin skeleton is necessary for the proper trafficking of Na-K-
ATPase to the BLM of the cell. In the present study,
ankyrin expression was markedly diminished in villus cells from the chronically inflamed intestine resulting in depolarization of
ankyrin-
G protein. The decrease of Na-K-
ATPase activity was comparable to that seen in
ankyrin knockdown IEC-18 cells. Therefore, altered localization of Na-K-
ATPase as a result of transcriptional down-regulation of
ankyrin-G mediates the down-regulation of Na-K-
ATPase activity during chronic intestinal
inflammation.