DIFFERENTIAL EXPRESSION OF SODIUM-PUMP CATALYTIC SUBUNITS IN THE LENSEPITHELIUM AND FIBERS

Na,K-ATPase in lens epithelium plays a key role in conducting sodium-p otassium transport, The purpose of this study was to test whether epit helium or fiber cells can synthesize new Na,K-ATPase protein in respon se to an increase of membrane permeability. Western blot methodology w as used to identify Na,K-ATPase alpha subunit polypeptides in membrane material isolated from lens cells, As judged by immunoblot density, e pithelial cell membrane material isolated from porcine lenses cultured 24 h with 1 mu M amphotericin B contained more Na,K-ATPase alpha subu nit polypeptide than epithelial material isolated from control lenses. This increase stemmed from the apparent synthesis of Na,K-ATPase alph a(2) isoform polypeptide by the epithelium; Na,K-ATPase alpha(1) isofo rm polypeptide abundance was not detectably altered. The apparent amph otericin B-induced expression of Na,K-ATPase alpha(2) was seen in lens epithelial cells but not fiber cells. This study suggests that the ep ithelium of the adult porcine lens may be capable of expressing additi onal sodium pump molecules of the az-subtype when membrane permeabilit y is increased.