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

Na,K-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 Na,K-ATPase protein in response to an increase of membrane permeability. Western blot methodology was used to identify Na,K-ATPase alpha 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 microM amphotericin B contained more Na,K-ATPase alpha subunit polypeptide than epithelial material isolated from control lenses. This increase stemmed from the apparent synthesis of Na,K-ATPase alpha 2 isoform polypeptide by the epithelium; Na,K-ATPase alpha 1 isoform polypeptide abundance was not detectably altered. The apparent amphotericin B-induced expression of Na,K-ATPase alpha 2 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 alpha 2-subtype when membrane permeability is increased.