Differential expression of sodium pump catalytic subunits in the lens epithelium and fibers

NaK-ATPase in lens epithelium plays a key role in conducting sodium-potassium transport. The purpose of this study was to test whether epithelium or fiber cells can synthesize new NaK-ATPase protein in response to an increase of membrane permeability. Western blot methodology was used to identify NaK-ATPase α subunit polypeptides in membrane material isolated from lens cells. As judged by immunoblot density, epithelial cell membrane material isolated from porcine lenses cultured 24 h with 1 μM amphotericin B contained more NaK-ATPase α subunit polypeptide than epithelial material isolated from control lenses. This increase stemmed from the apparent synthesis of NaK-ATPase α₂ isoform polypeptide by the epithelium; NaK-ATPase αi isoform polypeptide abundance was not detectably altered. The apparent amphotericin B-induced expression of NaK-ATPase α₂ was seen in lens epithelial cells but not fiber cells. This study suggests that the epithelium of the adult porcine lens may be capable of expressing additional sodium pump molecules of the α₂-inftype when membrane permeability is increased.